| Message ID | 1635264312-3796-4-git-send-email-olekstysh@gmail.com (mailing list archive) |
|---|---|
| State | Superseded |
| Headers | show |
| Series | xen: Add support of extended regions (safe ranges) on Arm | expand |
On Tue, 26 Oct 2021, Oleksandr Tyshchenko wrote: > From: Oleksandr Tyshchenko <oleksandr_tyshchenko@epam.com> > > The main reason of this change is that unpopulated-alloc > code cannot be used in its current form on Arm, but there > is a desire to reuse it to avoid wasting real RAM pages > for the grant/foreign mappings. > > The problem is that system "iomem_resource" is used for > the address space allocation, but the really unallocated > space can't be figured out precisely by the domain on Arm > without hypervisor involvement. For example, not all device > I/O regions are known by the time domain starts creating > grant/foreign mappings. And following the advise from > "iomem_resource" we might end up reusing these regions by > a mistake. So, the hypervisor which maintains the P2M for > the domain is in the best position to provide unused regions > of guest physical address space which could be safely used > to create grant/foreign mappings. > > Introduce new helper arch_xen_unpopulated_init() which purpose > is to create specific Xen resource based on the memory regions > provided by the hypervisor to be used as unused space for Xen > scratch pages. > > If arch doesn't implement arch_xen_unpopulated_init() to > initialize Xen resource the default "iomem_resource" will be used. > So the behavior on x86 won't be changed. > > Also fall back to allocate xenballooned pages (steal real RAM > pages) if we do not have any suitable resource to work with and > as the result we won't be able to provide unpopulated pages. > > Signed-off-by: Oleksandr Tyshchenko <oleksandr_tyshchenko@epam.com> > --- > Changes RFC -> V2: > - new patch, instead of > "[RFC PATCH 2/2] xen/unpopulated-alloc: Query hypervisor to provide unallocated space" > --- > drivers/xen/unpopulated-alloc.c | 89 +++++++++++++++++++++++++++++++++++++++-- > include/xen/xen.h | 2 + > 2 files changed, 88 insertions(+), 3 deletions(-) > > diff --git a/drivers/xen/unpopulated-alloc.c b/drivers/xen/unpopulated-alloc.c > index a03dc5b..1f1d8d8 100644 > --- a/drivers/xen/unpopulated-alloc.c > +++ b/drivers/xen/unpopulated-alloc.c > @@ -8,6 +8,7 @@ > > #include <asm/page.h> > > +#include <xen/balloon.h> > #include <xen/page.h> > #include <xen/xen.h> > > @@ -15,13 +16,29 @@ static DEFINE_MUTEX(list_lock); > static struct page *page_list; > static unsigned int list_count; > > +static struct resource *target_resource; > +static struct resource xen_resource = { > + .name = "Xen unused space", > +}; > + > +/* > + * If arch is not happy with system "iomem_resource" being used for > + * the region allocation it can provide it's own view by initializing > + * "xen_resource" with unused regions of guest physical address space > + * provided by the hypervisor. > + */ > +int __weak arch_xen_unpopulated_init(struct resource *res) > +{ > + return -ENOSYS; > +} > + > static int fill_list(unsigned int nr_pages) > { > struct dev_pagemap *pgmap; > - struct resource *res; > + struct resource *res, *tmp_res = NULL; > void *vaddr; > unsigned int i, alloc_pages = round_up(nr_pages, PAGES_PER_SECTION); > - int ret = -ENOMEM; > + int ret; > > res = kzalloc(sizeof(*res), GFP_KERNEL); > if (!res) > @@ -30,7 +47,7 @@ static int fill_list(unsigned int nr_pages) > res->name = "Xen scratch"; > res->flags = IORESOURCE_MEM | IORESOURCE_BUSY; > > - ret = allocate_resource(&iomem_resource, res, > + ret = allocate_resource(target_resource, res, > alloc_pages * PAGE_SIZE, 0, -1, > PAGES_PER_SECTION * PAGE_SIZE, NULL, NULL); > if (ret < 0) { > @@ -38,6 +55,31 @@ static int fill_list(unsigned int nr_pages) > goto err_resource; > } > > + /* > + * Reserve the region previously allocated from Xen resource to avoid > + * re-using it by someone else. > + */ > + if (target_resource != &iomem_resource) { > + tmp_res = kzalloc(sizeof(*tmp_res), GFP_KERNEL); > + if (!res) { > + ret = -ENOMEM; > + goto err_insert; > + } > + > + tmp_res->name = res->name; > + tmp_res->start = res->start; > + tmp_res->end = res->end; > + tmp_res->flags = res->flags; > + > + ret = insert_resource(&iomem_resource, tmp_res); > + if (ret < 0) { > + pr_err("Cannot insert IOMEM resource [%llx - %llx]\n", > + tmp_res->start, tmp_res->end); > + kfree(tmp_res); > + goto err_insert; > + } > + } I am a bit confused.. why do we need to do this? Who could be erroneously re-using the region? Are you saying that the next time allocate_resource is called it could find the same region again? It doesn't seem possible? > pgmap = kzalloc(sizeof(*pgmap), GFP_KERNEL); > if (!pgmap) { > ret = -ENOMEM; > @@ -95,12 +137,40 @@ static int fill_list(unsigned int nr_pages) > err_memremap: > kfree(pgmap); > err_pgmap: > + if (tmp_res) { > + release_resource(tmp_res); > + kfree(tmp_res); > + } > +err_insert: > release_resource(res); > err_resource: > kfree(res); > return ret; > } > > +static void unpopulated_init(void) > +{ > + static bool inited = false; initialized = false > + int ret; > + > + if (inited) > + return; > + > + /* > + * Try to initialize Xen resource the first and fall back to default > + * resource if arch doesn't offer one. > + */ > + ret = arch_xen_unpopulated_init(&xen_resource); > + if (!ret) > + target_resource = &xen_resource; > + else if (ret == -ENOSYS) > + target_resource = &iomem_resource; > + else > + pr_err("Cannot initialize Xen resource\n"); > + > + inited = true; > +} Would it make sense to call unpopulated_init from an init function, rather than every time xen_alloc_unpopulated_pages is called? > /** > * xen_alloc_unpopulated_pages - alloc unpopulated pages > * @nr_pages: Number of pages > @@ -112,6 +182,16 @@ int xen_alloc_unpopulated_pages(unsigned int nr_pages, struct page **pages) > unsigned int i; > int ret = 0; > > + unpopulated_init(); > + > + /* > + * Fall back to default behavior if we do not have any suitable resource > + * to allocate required region from and as the result we won't be able to > + * construct pages. > + */ > + if (!target_resource) > + return alloc_xenballooned_pages(nr_pages, pages); The commit message says that the behavior on x86 doesn't change but this seems to be a change that could impact x86? > mutex_lock(&list_lock); > if (list_count < nr_pages) { > ret = fill_list(nr_pages - list_count); > @@ -159,6 +239,9 @@ void xen_free_unpopulated_pages(unsigned int nr_pages, struct page **pages) > { > unsigned int i; > > + if (!target_resource) > + return free_xenballooned_pages(nr_pages, pages); > + > mutex_lock(&list_lock); > for (i = 0; i < nr_pages; i++) { > pages[i]->zone_device_data = page_list; > diff --git a/include/xen/xen.h b/include/xen/xen.h > index 43efba0..55d2ef8 100644 > --- a/include/xen/xen.h > +++ b/include/xen/xen.h > @@ -55,6 +55,8 @@ extern u64 xen_saved_max_mem_size; > #ifdef CONFIG_XEN_UNPOPULATED_ALLOC > int xen_alloc_unpopulated_pages(unsigned int nr_pages, struct page **pages); > void xen_free_unpopulated_pages(unsigned int nr_pages, struct page **pages); > +struct resource; This is to avoid having to #include linux/ioport.h, right? Is it a problem or is it just to minimize the headers dependencies? It looks like adding #include <linux/ioport.h> below #include <linux/types.h> in include/xen/xen.h would work too. I am not sure what is the best way though, I'll let Juergen comment. > +int arch_xen_unpopulated_init(struct resource *res); > #else > #define xen_alloc_unpopulated_pages alloc_xenballooned_pages > #define xen_free_unpopulated_pages free_xenballooned_pages > -- > 2.7.4 >
On 10/26/21 12:05 PM, Oleksandr Tyshchenko wrote: > > +static void unpopulated_init(void) > +{ > + static bool inited = false; > + int ret; > + > + if (inited) > + return; > + > + /* > + * Try to initialize Xen resource the first and fall back to default > + * resource if arch doesn't offer one. > + */ > + ret = arch_xen_unpopulated_init(&xen_resource); > + if (!ret) > + target_resource = &xen_resource; > + else if (ret == -ENOSYS) > + target_resource = &iomem_resource; > + else > + pr_err("Cannot initialize Xen resource\n"); I'd pass target_resource as a parameter to arch_xen_unpopulated_init() instead. Default routine will assign it iomem_resource and you won't have to deal with -ENOSYS. Also, what happens in case of error? Is it fatal? I don't think your changes in fill_list() will work. > + > + inited = true; I agree with Stefano in that it would be better to call this from an init function, and you won't have t worry about multiple calls here. -boris
On 28.10.21 19:37, Stefano Stabellini wrote: Hi Stefano I am sorry for the late response. > On Tue, 26 Oct 2021, Oleksandr Tyshchenko wrote: >> From: Oleksandr Tyshchenko <oleksandr_tyshchenko@epam.com> >> >> The main reason of this change is that unpopulated-alloc >> code cannot be used in its current form on Arm, but there >> is a desire to reuse it to avoid wasting real RAM pages >> for the grant/foreign mappings. >> >> The problem is that system "iomem_resource" is used for >> the address space allocation, but the really unallocated >> space can't be figured out precisely by the domain on Arm >> without hypervisor involvement. For example, not all device >> I/O regions are known by the time domain starts creating >> grant/foreign mappings. And following the advise from >> "iomem_resource" we might end up reusing these regions by >> a mistake. So, the hypervisor which maintains the P2M for >> the domain is in the best position to provide unused regions >> of guest physical address space which could be safely used >> to create grant/foreign mappings. >> >> Introduce new helper arch_xen_unpopulated_init() which purpose >> is to create specific Xen resource based on the memory regions >> provided by the hypervisor to be used as unused space for Xen >> scratch pages. >> >> If arch doesn't implement arch_xen_unpopulated_init() to >> initialize Xen resource the default "iomem_resource" will be used. >> So the behavior on x86 won't be changed. >> >> Also fall back to allocate xenballooned pages (steal real RAM >> pages) if we do not have any suitable resource to work with and >> as the result we won't be able to provide unpopulated pages. >> >> Signed-off-by: Oleksandr Tyshchenko <oleksandr_tyshchenko@epam.com> >> --- >> Changes RFC -> V2: >> - new patch, instead of >> "[RFC PATCH 2/2] xen/unpopulated-alloc: Query hypervisor to provide unallocated space" >> --- >> drivers/xen/unpopulated-alloc.c | 89 +++++++++++++++++++++++++++++++++++++++-- >> include/xen/xen.h | 2 + >> 2 files changed, 88 insertions(+), 3 deletions(-) >> >> diff --git a/drivers/xen/unpopulated-alloc.c b/drivers/xen/unpopulated-alloc.c >> index a03dc5b..1f1d8d8 100644 >> --- a/drivers/xen/unpopulated-alloc.c >> +++ b/drivers/xen/unpopulated-alloc.c >> @@ -8,6 +8,7 @@ >> >> #include <asm/page.h> >> >> +#include <xen/balloon.h> >> #include <xen/page.h> >> #include <xen/xen.h> >> >> @@ -15,13 +16,29 @@ static DEFINE_MUTEX(list_lock); >> static struct page *page_list; >> static unsigned int list_count; >> >> +static struct resource *target_resource; >> +static struct resource xen_resource = { >> + .name = "Xen unused space", >> +}; >> + >> +/* >> + * If arch is not happy with system "iomem_resource" being used for >> + * the region allocation it can provide it's own view by initializing >> + * "xen_resource" with unused regions of guest physical address space >> + * provided by the hypervisor. >> + */ >> +int __weak arch_xen_unpopulated_init(struct resource *res) >> +{ >> + return -ENOSYS; >> +} >> + >> static int fill_list(unsigned int nr_pages) >> { >> struct dev_pagemap *pgmap; >> - struct resource *res; >> + struct resource *res, *tmp_res = NULL; >> void *vaddr; >> unsigned int i, alloc_pages = round_up(nr_pages, PAGES_PER_SECTION); >> - int ret = -ENOMEM; >> + int ret; >> >> res = kzalloc(sizeof(*res), GFP_KERNEL); >> if (!res) >> @@ -30,7 +47,7 @@ static int fill_list(unsigned int nr_pages) >> res->name = "Xen scratch"; >> res->flags = IORESOURCE_MEM | IORESOURCE_BUSY; >> >> - ret = allocate_resource(&iomem_resource, res, >> + ret = allocate_resource(target_resource, res, >> alloc_pages * PAGE_SIZE, 0, -1, >> PAGES_PER_SECTION * PAGE_SIZE, NULL, NULL); >> if (ret < 0) { >> @@ -38,6 +55,31 @@ static int fill_list(unsigned int nr_pages) >> goto err_resource; >> } >> >> + /* >> + * Reserve the region previously allocated from Xen resource to avoid >> + * re-using it by someone else. >> + */ >> + if (target_resource != &iomem_resource) { >> + tmp_res = kzalloc(sizeof(*tmp_res), GFP_KERNEL); >> + if (!res) { >> + ret = -ENOMEM; >> + goto err_insert; >> + } >> + >> + tmp_res->name = res->name; >> + tmp_res->start = res->start; >> + tmp_res->end = res->end; >> + tmp_res->flags = res->flags; >> + >> + ret = insert_resource(&iomem_resource, tmp_res); >> + if (ret < 0) { >> + pr_err("Cannot insert IOMEM resource [%llx - %llx]\n", >> + tmp_res->start, tmp_res->end); >> + kfree(tmp_res); >> + goto err_insert; >> + } >> + } > I am a bit confused.. why do we need to do this? Who could be > erroneously re-using the region? Are you saying that the next time > allocate_resource is called it could find the same region again? It > doesn't seem possible? No, as I understand the allocate_resource() being called for the same root resource won't provide the same region... We only need to do this (insert the region into "iomem_resource") if we allocated it from our *internal* "xen_resource", as *global* "iomem_resource" (which is used everywhere) is not aware of that region has been already allocated. So inserting a region here we reserving it, otherwise it could be reused elsewhere. > > >> pgmap = kzalloc(sizeof(*pgmap), GFP_KERNEL); >> if (!pgmap) { >> ret = -ENOMEM; >> @@ -95,12 +137,40 @@ static int fill_list(unsigned int nr_pages) >> err_memremap: >> kfree(pgmap); >> err_pgmap: >> + if (tmp_res) { >> + release_resource(tmp_res); >> + kfree(tmp_res); >> + } >> +err_insert: >> release_resource(res); >> err_resource: >> kfree(res); >> return ret; >> } >> >> +static void unpopulated_init(void) >> +{ >> + static bool inited = false; > initialized = false ok. > > >> + int ret; >> + >> + if (inited) >> + return; >> + >> + /* >> + * Try to initialize Xen resource the first and fall back to default >> + * resource if arch doesn't offer one. >> + */ >> + ret = arch_xen_unpopulated_init(&xen_resource); >> + if (!ret) >> + target_resource = &xen_resource; >> + else if (ret == -ENOSYS) >> + target_resource = &iomem_resource; >> + else >> + pr_err("Cannot initialize Xen resource\n"); >> + >> + inited = true; >> +} > Would it make sense to call unpopulated_init from an init function, > rather than every time xen_alloc_unpopulated_pages is called? Good point, thank you. Will do. To be honest, I also don't like the current approach much. > > >> /** >> * xen_alloc_unpopulated_pages - alloc unpopulated pages >> * @nr_pages: Number of pages >> @@ -112,6 +182,16 @@ int xen_alloc_unpopulated_pages(unsigned int nr_pages, struct page **pages) >> unsigned int i; >> int ret = 0; >> >> + unpopulated_init(); >> + >> + /* >> + * Fall back to default behavior if we do not have any suitable resource >> + * to allocate required region from and as the result we won't be able to >> + * construct pages. >> + */ >> + if (!target_resource) >> + return alloc_xenballooned_pages(nr_pages, pages); > The commit message says that the behavior on x86 doesn't change but this > seems to be a change that could impact x86? I don't think, however I didn't tested on x86 and might be wrong, but according to the current patch, on x86 the "target_resource" is always valid and points to the "iomem_resource" as arch_xen_unpopulated_init() is not implemented. So there won't be any fallback to use alloc_(free)_xenballooned_pages() here and fill_list() will behave as usual. You raised a really good question, on Arm we need a fallback to balloon out RAM pages again if hypervisor doesn't provide extended regions (we run on old version, no unused regions with reasonable size, etc), so I decided to put a fallback code here, an indicator of the failure is invalid "target_resource". I noticed the patch which is about to be upstreamed that removes alloc_(free)xenballooned_pages API [1]. Right now I have no idea how/where this fallback could be implemented as this is under build option control (CONFIG_XEN_UNPOPULATED_ALLOC). So the API with the same name is either used for unpopulated pages (if set) or ballooned pages (if not set). I would appreciate suggestions regarding that. I am wondering would it be possible and correctly to have both mechanisms (unpopulated and ballooned) enabled by default and some init code to decide which one to use at runtime or some sort? > >> mutex_lock(&list_lock); >> if (list_count < nr_pages) { >> ret = fill_list(nr_pages - list_count); >> @@ -159,6 +239,9 @@ void xen_free_unpopulated_pages(unsigned int nr_pages, struct page **pages) >> { >> unsigned int i; >> >> + if (!target_resource) >> + return free_xenballooned_pages(nr_pages, pages); >> + >> mutex_lock(&list_lock); >> for (i = 0; i < nr_pages; i++) { >> pages[i]->zone_device_data = page_list; >> diff --git a/include/xen/xen.h b/include/xen/xen.h >> index 43efba0..55d2ef8 100644 >> --- a/include/xen/xen.h >> +++ b/include/xen/xen.h >> @@ -55,6 +55,8 @@ extern u64 xen_saved_max_mem_size; >> #ifdef CONFIG_XEN_UNPOPULATED_ALLOC >> int xen_alloc_unpopulated_pages(unsigned int nr_pages, struct page **pages); >> void xen_free_unpopulated_pages(unsigned int nr_pages, struct page **pages); >> +struct resource; > This is to avoid having to #include linux/ioport.h, right? Is it a > problem or is it just to minimize the headers dependencies? > > It looks like adding #include <linux/ioport.h> below #include > <linux/types.h> in include/xen/xen.h would work too. I am not sure what > is the best way though, I'll let Juergen comment. Yes, the initial reason to use forward declaration here was to minimize the headers dependencies. I have rechecked, your suggestion works as well, thank you. So I would be OK either way, let's wait for other opinions. > > >> +int arch_xen_unpopulated_init(struct resource *res); >> #else >> #define xen_alloc_unpopulated_pages alloc_xenballooned_pages >> #define xen_free_unpopulated_pages free_xenballooned_pages >> -- >> 2.7.4 >> [1] https://lore.kernel.org/lkml/20211102092234.17852-1-jgross@suse.com/
On 28.10.21 22:08, Boris Ostrovsky wrote: Hi Boris I am sorry for the late response. > > On 10/26/21 12:05 PM, Oleksandr Tyshchenko wrote: >> +static void unpopulated_init(void) >> +{ >> + static bool inited = false; >> + int ret; >> + >> + if (inited) >> + return; >> + >> + /* >> + * Try to initialize Xen resource the first and fall back to >> default >> + * resource if arch doesn't offer one. >> + */ >> + ret = arch_xen_unpopulated_init(&xen_resource); >> + if (!ret) >> + target_resource = &xen_resource; >> + else if (ret == -ENOSYS) >> + target_resource = &iomem_resource; >> + else >> + pr_err("Cannot initialize Xen resource\n"); > > > I'd pass target_resource as a parameter to arch_xen_unpopulated_init() > instead. Default routine will assign it iomem_resource and you won't > have to deal with -ENOSYS. That would be much better, thank you. Will do. > > > > Also, what happens in case of error? Is it fatal? I don't think your > changes in fill_list() will work. The error is fatal as we don't have a suitable resource to allocate a region from, and yes, the fill_list() must not be called. > > > >> + >> + inited = true; > > > I agree with Stefano in that it would be better to call this from an > init function, and you won't have t worry about multiple calls here. Yes, that's good point, thank you. Will do. > > > > -boris
On Tue, 9 Nov 2021, Oleksandr wrote: > On 28.10.21 19:37, Stefano Stabellini wrote: > > Hi Stefano > > I am sorry for the late response. > > > On Tue, 26 Oct 2021, Oleksandr Tyshchenko wrote: > > > From: Oleksandr Tyshchenko <oleksandr_tyshchenko@epam.com> > > > > > > The main reason of this change is that unpopulated-alloc > > > code cannot be used in its current form on Arm, but there > > > is a desire to reuse it to avoid wasting real RAM pages > > > for the grant/foreign mappings. > > > > > > The problem is that system "iomem_resource" is used for > > > the address space allocation, but the really unallocated > > > space can't be figured out precisely by the domain on Arm > > > without hypervisor involvement. For example, not all device > > > I/O regions are known by the time domain starts creating > > > grant/foreign mappings. And following the advise from > > > "iomem_resource" we might end up reusing these regions by > > > a mistake. So, the hypervisor which maintains the P2M for > > > the domain is in the best position to provide unused regions > > > of guest physical address space which could be safely used > > > to create grant/foreign mappings. > > > > > > Introduce new helper arch_xen_unpopulated_init() which purpose > > > is to create specific Xen resource based on the memory regions > > > provided by the hypervisor to be used as unused space for Xen > > > scratch pages. > > > > > > If arch doesn't implement arch_xen_unpopulated_init() to > > > initialize Xen resource the default "iomem_resource" will be used. > > > So the behavior on x86 won't be changed. > > > > > > Also fall back to allocate xenballooned pages (steal real RAM > > > pages) if we do not have any suitable resource to work with and > > > as the result we won't be able to provide unpopulated pages. > > > > > > Signed-off-by: Oleksandr Tyshchenko <oleksandr_tyshchenko@epam.com> > > > --- > > > Changes RFC -> V2: > > > - new patch, instead of > > > "[RFC PATCH 2/2] xen/unpopulated-alloc: Query hypervisor to provide > > > unallocated space" > > > --- > > > drivers/xen/unpopulated-alloc.c | 89 > > > +++++++++++++++++++++++++++++++++++++++-- > > > include/xen/xen.h | 2 + > > > 2 files changed, 88 insertions(+), 3 deletions(-) > > > > > > diff --git a/drivers/xen/unpopulated-alloc.c > > > b/drivers/xen/unpopulated-alloc.c > > > index a03dc5b..1f1d8d8 100644 > > > --- a/drivers/xen/unpopulated-alloc.c > > > +++ b/drivers/xen/unpopulated-alloc.c > > > @@ -8,6 +8,7 @@ > > > #include <asm/page.h> > > > +#include <xen/balloon.h> > > > #include <xen/page.h> > > > #include <xen/xen.h> > > > @@ -15,13 +16,29 @@ static DEFINE_MUTEX(list_lock); > > > static struct page *page_list; > > > static unsigned int list_count; > > > +static struct resource *target_resource; > > > +static struct resource xen_resource = { > > > + .name = "Xen unused space", > > > +}; > > > + > > > +/* > > > + * If arch is not happy with system "iomem_resource" being used for > > > + * the region allocation it can provide it's own view by initializing > > > + * "xen_resource" with unused regions of guest physical address space > > > + * provided by the hypervisor. > > > + */ > > > +int __weak arch_xen_unpopulated_init(struct resource *res) > > > +{ > > > + return -ENOSYS; > > > +} > > > + > > > static int fill_list(unsigned int nr_pages) > > > { > > > struct dev_pagemap *pgmap; > > > - struct resource *res; > > > + struct resource *res, *tmp_res = NULL; > > > void *vaddr; > > > unsigned int i, alloc_pages = round_up(nr_pages, PAGES_PER_SECTION); > > > - int ret = -ENOMEM; > > > + int ret; > > > res = kzalloc(sizeof(*res), GFP_KERNEL); > > > if (!res) > > > @@ -30,7 +47,7 @@ static int fill_list(unsigned int nr_pages) > > > res->name = "Xen scratch"; > > > res->flags = IORESOURCE_MEM | IORESOURCE_BUSY; > > > - ret = allocate_resource(&iomem_resource, res, > > > + ret = allocate_resource(target_resource, res, > > > alloc_pages * PAGE_SIZE, 0, -1, > > > PAGES_PER_SECTION * PAGE_SIZE, NULL, NULL); > > > if (ret < 0) { > > > @@ -38,6 +55,31 @@ static int fill_list(unsigned int nr_pages) > > > goto err_resource; > > > } > > > + /* > > > + * Reserve the region previously allocated from Xen resource to avoid > > > + * re-using it by someone else. > > > + */ > > > + if (target_resource != &iomem_resource) { > > > + tmp_res = kzalloc(sizeof(*tmp_res), GFP_KERNEL); > > > + if (!res) { > > > + ret = -ENOMEM; > > > + goto err_insert; > > > + } > > > + > > > + tmp_res->name = res->name; > > > + tmp_res->start = res->start; > > > + tmp_res->end = res->end; > > > + tmp_res->flags = res->flags; > > > + > > > + ret = insert_resource(&iomem_resource, tmp_res); > > > + if (ret < 0) { > > > + pr_err("Cannot insert IOMEM resource [%llx - %llx]\n", > > > + tmp_res->start, tmp_res->end); > > > + kfree(tmp_res); > > > + goto err_insert; > > > + } > > > + } > > I am a bit confused.. why do we need to do this? Who could be > > erroneously re-using the region? Are you saying that the next time > > allocate_resource is called it could find the same region again? It > > doesn't seem possible? > > > No, as I understand the allocate_resource() being called for the same root > resource won't provide the same region... We only need to do this (insert the > region into "iomem_resource") if we allocated it from our *internal* > "xen_resource", as *global* "iomem_resource" (which is used everywhere) is not > aware of that region has been already allocated. So inserting a region here we > reserving it, otherwise it could be reused elsewhere. But elsewhere where? Let's say that allocate_resource allocates a range from xen_resource. From reading the code, it doesn't look like iomem_resource would have that range because the extended regions described under /hypervisor are not added automatically to iomem_resource. So what if we don't call insert_resource? Nothing could allocate the same range because iomem_resource doesn't have it at all and xen_resource is not used anywhere if not here. What am I missing? Or maybe it is the other way around: core Linux code assumes everything is described in iomem_resource so something under kernel/ or mm/ would crash if we start using a page pointing to an address missing from iomem_resource? > > > pgmap = kzalloc(sizeof(*pgmap), GFP_KERNEL); > > > if (!pgmap) { > > > ret = -ENOMEM; > > > @@ -95,12 +137,40 @@ static int fill_list(unsigned int nr_pages) > > > err_memremap: > > > kfree(pgmap); > > > err_pgmap: > > > + if (tmp_res) { > > > + release_resource(tmp_res); > > > + kfree(tmp_res); > > > + } > > > +err_insert: > > > release_resource(res); > > > err_resource: > > > kfree(res); > > > return ret; > > > } > > > +static void unpopulated_init(void) > > > +{ > > > + static bool inited = false; > > initialized = false > > ok. > > > > > > > > > + int ret; > > > + > > > + if (inited) > > > + return; > > > + > > > + /* > > > + * Try to initialize Xen resource the first and fall back to default > > > + * resource if arch doesn't offer one. > > > + */ > > > + ret = arch_xen_unpopulated_init(&xen_resource); > > > + if (!ret) > > > + target_resource = &xen_resource; > > > + else if (ret == -ENOSYS) > > > + target_resource = &iomem_resource; > > > + else > > > + pr_err("Cannot initialize Xen resource\n"); > > > + > > > + inited = true; > > > +} > > Would it make sense to call unpopulated_init from an init function, > > rather than every time xen_alloc_unpopulated_pages is called? > > Good point, thank you. Will do. To be honest, I also don't like the current > approach much. > > > > > > > > > /** > > > * xen_alloc_unpopulated_pages - alloc unpopulated pages > > > * @nr_pages: Number of pages > > > @@ -112,6 +182,16 @@ int xen_alloc_unpopulated_pages(unsigned int > > > nr_pages, struct page **pages) > > > unsigned int i; > > > int ret = 0; > > > + unpopulated_init(); > > > + > > > + /* > > > + * Fall back to default behavior if we do not have any suitable > > > resource > > > + * to allocate required region from and as the result we won't be able > > > to > > > + * construct pages. > > > + */ > > > + if (!target_resource) > > > + return alloc_xenballooned_pages(nr_pages, pages); > > The commit message says that the behavior on x86 doesn't change but this > > seems to be a change that could impact x86? > I don't think, however I didn't tested on x86 and might be wrong, but > according to the current patch, on x86 the "target_resource" is always valid > and points to the "iomem_resource" as arch_xen_unpopulated_init() is not > implemented. So there won't be any fallback to use > alloc_(free)_xenballooned_pages() here and fill_list() will behave as usual. If target_resource is always valid, then we don't need this special check. In fact, the condition should never be true. > You raised a really good question, on Arm we need a fallback to balloon out > RAM pages again if hypervisor doesn't provide extended regions (we run on old > version, no unused regions with reasonable size, etc), so I decided to put a > fallback code here, an indicator of the failure is invalid "target_resource". I think it is unnecessary as we already assume today that &iomem_resource is always available. > I noticed the patch which is about to be upstreamed that removes > alloc_(free)xenballooned_pages API [1]. Right now I have no idea how/where > this fallback could be implemented as this is under build option control > (CONFIG_XEN_UNPOPULATED_ALLOC). So the API with the same name is either used > for unpopulated pages (if set) or ballooned pages (if not set). I would > appreciate suggestions regarding that. I am wondering would it be possible and > correctly to have both mechanisms (unpopulated and ballooned) enabled by > default and some init code to decide which one to use at runtime or some sort? I would keep it simple and remove the fallback from this patch. So: - if not CONFIG_XEN_UNPOPULATED_ALLOC, then balloon - if CONFIG_XEN_UNPOPULATED_ALLOC, then - xen_resource if present - otherwise iomem_resource The xen_resource/iomem_resource config can be done at init time using target_resource. At runtime, target_resource is always != NULL so we just go ahead and use it. > > > > > mutex_lock(&list_lock); > > > if (list_count < nr_pages) { > > > ret = fill_list(nr_pages - list_count); > > > @@ -159,6 +239,9 @@ void xen_free_unpopulated_pages(unsigned int nr_pages, > > > struct page **pages) > > > { > > > unsigned int i; > > > + if (!target_resource) > > > + return free_xenballooned_pages(nr_pages, pages); > > > + > > > mutex_lock(&list_lock); > > > for (i = 0; i < nr_pages; i++) { > > > pages[i]->zone_device_data = page_list; > > > diff --git a/include/xen/xen.h b/include/xen/xen.h > > > index 43efba0..55d2ef8 100644 > > > --- a/include/xen/xen.h > > > +++ b/include/xen/xen.h > > > @@ -55,6 +55,8 @@ extern u64 xen_saved_max_mem_size; > > > #ifdef CONFIG_XEN_UNPOPULATED_ALLOC > > > int xen_alloc_unpopulated_pages(unsigned int nr_pages, struct page > > > **pages); > > > void xen_free_unpopulated_pages(unsigned int nr_pages, struct page > > > **pages); > > > +struct resource; > > This is to avoid having to #include linux/ioport.h, right? Is it a > > problem or is it just to minimize the headers dependencies? > > > > It looks like adding #include <linux/ioport.h> below #include > > <linux/types.h> in include/xen/xen.h would work too. I am not sure what > > is the best way though, I'll let Juergen comment. > Yes, the initial reason to use forward declaration here was to minimize the > headers dependencies. > I have rechecked, your suggestion works as well, thank you. So I would be OK > either way, let's wait for other opinions. > > > > > > > > > +int arch_xen_unpopulated_init(struct resource *res); > > > #else > > > #define xen_alloc_unpopulated_pages alloc_xenballooned_pages > > > #define xen_free_unpopulated_pages free_xenballooned_pages > > > -- > > > 2.7.4 > > > > > [1] https://lore.kernel.org/lkml/20211102092234.17852-1-jgross@suse.com/ > > -- > Regards, > > Oleksandr Tyshchenko >
On 19.11.21 02:59, Stefano Stabellini wrote: Hi Stefano > On Tue, 9 Nov 2021, Oleksandr wrote: >> On 28.10.21 19:37, Stefano Stabellini wrote: >> >> Hi Stefano >> >> I am sorry for the late response. >> >>> On Tue, 26 Oct 2021, Oleksandr Tyshchenko wrote: >>>> From: Oleksandr Tyshchenko <oleksandr_tyshchenko@epam.com> >>>> >>>> The main reason of this change is that unpopulated-alloc >>>> code cannot be used in its current form on Arm, but there >>>> is a desire to reuse it to avoid wasting real RAM pages >>>> for the grant/foreign mappings. >>>> >>>> The problem is that system "iomem_resource" is used for >>>> the address space allocation, but the really unallocated >>>> space can't be figured out precisely by the domain on Arm >>>> without hypervisor involvement. For example, not all device >>>> I/O regions are known by the time domain starts creating >>>> grant/foreign mappings. And following the advise from >>>> "iomem_resource" we might end up reusing these regions by >>>> a mistake. So, the hypervisor which maintains the P2M for >>>> the domain is in the best position to provide unused regions >>>> of guest physical address space which could be safely used >>>> to create grant/foreign mappings. >>>> >>>> Introduce new helper arch_xen_unpopulated_init() which purpose >>>> is to create specific Xen resource based on the memory regions >>>> provided by the hypervisor to be used as unused space for Xen >>>> scratch pages. >>>> >>>> If arch doesn't implement arch_xen_unpopulated_init() to >>>> initialize Xen resource the default "iomem_resource" will be used. >>>> So the behavior on x86 won't be changed. >>>> >>>> Also fall back to allocate xenballooned pages (steal real RAM >>>> pages) if we do not have any suitable resource to work with and >>>> as the result we won't be able to provide unpopulated pages. >>>> >>>> Signed-off-by: Oleksandr Tyshchenko <oleksandr_tyshchenko@epam.com> >>>> --- >>>> Changes RFC -> V2: >>>> - new patch, instead of >>>> "[RFC PATCH 2/2] xen/unpopulated-alloc: Query hypervisor to provide >>>> unallocated space" >>>> --- >>>> drivers/xen/unpopulated-alloc.c | 89 >>>> +++++++++++++++++++++++++++++++++++++++-- >>>> include/xen/xen.h | 2 + >>>> 2 files changed, 88 insertions(+), 3 deletions(-) >>>> >>>> diff --git a/drivers/xen/unpopulated-alloc.c >>>> b/drivers/xen/unpopulated-alloc.c >>>> index a03dc5b..1f1d8d8 100644 >>>> --- a/drivers/xen/unpopulated-alloc.c >>>> +++ b/drivers/xen/unpopulated-alloc.c >>>> @@ -8,6 +8,7 @@ >>>> #include <asm/page.h> >>>> +#include <xen/balloon.h> >>>> #include <xen/page.h> >>>> #include <xen/xen.h> >>>> @@ -15,13 +16,29 @@ static DEFINE_MUTEX(list_lock); >>>> static struct page *page_list; >>>> static unsigned int list_count; >>>> +static struct resource *target_resource; >>>> +static struct resource xen_resource = { >>>> + .name = "Xen unused space", >>>> +}; >>>> + >>>> +/* >>>> + * If arch is not happy with system "iomem_resource" being used for >>>> + * the region allocation it can provide it's own view by initializing >>>> + * "xen_resource" with unused regions of guest physical address space >>>> + * provided by the hypervisor. >>>> + */ >>>> +int __weak arch_xen_unpopulated_init(struct resource *res) >>>> +{ >>>> + return -ENOSYS; >>>> +} >>>> + >>>> static int fill_list(unsigned int nr_pages) >>>> { >>>> struct dev_pagemap *pgmap; >>>> - struct resource *res; >>>> + struct resource *res, *tmp_res = NULL; >>>> void *vaddr; >>>> unsigned int i, alloc_pages = round_up(nr_pages, PAGES_PER_SECTION); >>>> - int ret = -ENOMEM; >>>> + int ret; >>>> res = kzalloc(sizeof(*res), GFP_KERNEL); >>>> if (!res) >>>> @@ -30,7 +47,7 @@ static int fill_list(unsigned int nr_pages) >>>> res->name = "Xen scratch"; >>>> res->flags = IORESOURCE_MEM | IORESOURCE_BUSY; >>>> - ret = allocate_resource(&iomem_resource, res, >>>> + ret = allocate_resource(target_resource, res, >>>> alloc_pages * PAGE_SIZE, 0, -1, >>>> PAGES_PER_SECTION * PAGE_SIZE, NULL, NULL); >>>> if (ret < 0) { >>>> @@ -38,6 +55,31 @@ static int fill_list(unsigned int nr_pages) >>>> goto err_resource; >>>> } >>>> + /* >>>> + * Reserve the region previously allocated from Xen resource to avoid >>>> + * re-using it by someone else. >>>> + */ >>>> + if (target_resource != &iomem_resource) { >>>> + tmp_res = kzalloc(sizeof(*tmp_res), GFP_KERNEL); >>>> + if (!res) { >>>> + ret = -ENOMEM; >>>> + goto err_insert; >>>> + } >>>> + >>>> + tmp_res->name = res->name; >>>> + tmp_res->start = res->start; >>>> + tmp_res->end = res->end; >>>> + tmp_res->flags = res->flags; >>>> + >>>> + ret = insert_resource(&iomem_resource, tmp_res); >>>> + if (ret < 0) { >>>> + pr_err("Cannot insert IOMEM resource [%llx - %llx]\n", >>>> + tmp_res->start, tmp_res->end); >>>> + kfree(tmp_res); >>>> + goto err_insert; >>>> + } >>>> + } >>> I am a bit confused.. why do we need to do this? Who could be >>> erroneously re-using the region? Are you saying that the next time >>> allocate_resource is called it could find the same region again? It >>> doesn't seem possible? >> >> No, as I understand the allocate_resource() being called for the same root >> resource won't provide the same region... We only need to do this (insert the >> region into "iomem_resource") if we allocated it from our *internal* >> "xen_resource", as *global* "iomem_resource" (which is used everywhere) is not >> aware of that region has been already allocated. So inserting a region here we >> reserving it, otherwise it could be reused elsewhere. > But elsewhere where? I think, theoretically everywhere where allocate_resource(&iomem_resource, ...) is called. > Let's say that allocate_resource allocates a range from xen_resource. > From reading the code, it doesn't look like iomem_resource would have > that range because the extended regions described under /hypervisor are > not added automatically to iomem_resource. > > So what if we don't call insert_resource? Nothing could allocate the > same range because iomem_resource doesn't have it at all and > xen_resource is not used anywhere if not here. > > What am I missing? Below my understanding which, of course, might be wrong. If we don't claim resource by calling insert_resource (or even request_resource) here then the same range could be allocated everywhere where allocate_resource(&iomem_resource, ...) is called. I don't see what prevents the same range from being allocated. Why actually allocate_resource(&iomem_resource, ...) can't provide the same range if it is free (not-reserved-yet) from it's PoV? The comment above allocate_resource() says "allocate empty slot in the resource tree given range & alignment". So this "empty slot" could be exactly the same range. I experimented with that a bit trying to call allocate_resource(&iomem_resource, ...) several times in another place to see what ranges it returns in both cases (w/ and w/o calling insert_resource here). So an experiment confirmed (of course, if I made it correctly) that the same range could be allocated if we didn't call insert_resource() here. And as I understand there is nothing strange here, as iomem_resource covers all address space initially (0, -1) and everything *not* inserted/requested (in other words, reserved) yet is considered as free and could be provided if fits constraints. Or I really missed something? It feels to me that it would be better to call request_resource() instead of insert_resource(). It seems, that if no conflict happens both functions will behave in same way, but in case of conflict if the conflicting resource entirely fit the new resource the former will return an error. I think, this way we will be able to detect that a range we are trying to reserve is already present and bail out early. > > Or maybe it is the other way around: core Linux code assumes everything > is described in iomem_resource so something under kernel/ or mm/ would > crash if we start using a page pointing to an address missing from > iomem_resource? > > >>>> pgmap = kzalloc(sizeof(*pgmap), GFP_KERNEL); >>>> if (!pgmap) { >>>> ret = -ENOMEM; >>>> @@ -95,12 +137,40 @@ static int fill_list(unsigned int nr_pages) >>>> err_memremap: >>>> kfree(pgmap); >>>> err_pgmap: >>>> + if (tmp_res) { >>>> + release_resource(tmp_res); >>>> + kfree(tmp_res); >>>> + } >>>> +err_insert: >>>> release_resource(res); >>>> err_resource: >>>> kfree(res); >>>> return ret; >>>> } >>>> +static void unpopulated_init(void) >>>> +{ >>>> + static bool inited = false; >>> initialized = false >> ok. >> >> >>> >>>> + int ret; >>>> + >>>> + if (inited) >>>> + return; >>>> + >>>> + /* >>>> + * Try to initialize Xen resource the first and fall back to default >>>> + * resource if arch doesn't offer one. >>>> + */ >>>> + ret = arch_xen_unpopulated_init(&xen_resource); >>>> + if (!ret) >>>> + target_resource = &xen_resource; >>>> + else if (ret == -ENOSYS) >>>> + target_resource = &iomem_resource; >>>> + else >>>> + pr_err("Cannot initialize Xen resource\n"); >>>> + >>>> + inited = true; >>>> +} >>> Would it make sense to call unpopulated_init from an init function, >>> rather than every time xen_alloc_unpopulated_pages is called? >> Good point, thank you. Will do. To be honest, I also don't like the current >> approach much. >> >> >>> >>>> /** >>>> * xen_alloc_unpopulated_pages - alloc unpopulated pages >>>> * @nr_pages: Number of pages >>>> @@ -112,6 +182,16 @@ int xen_alloc_unpopulated_pages(unsigned int >>>> nr_pages, struct page **pages) >>>> unsigned int i; >>>> int ret = 0; >>>> + unpopulated_init(); >>>> + >>>> + /* >>>> + * Fall back to default behavior if we do not have any suitable >>>> resource >>>> + * to allocate required region from and as the result we won't be able >>>> to >>>> + * construct pages. >>>> + */ >>>> + if (!target_resource) >>>> + return alloc_xenballooned_pages(nr_pages, pages); >>> The commit message says that the behavior on x86 doesn't change but this >>> seems to be a change that could impact x86? >> I don't think, however I didn't tested on x86 and might be wrong, but >> according to the current patch, on x86 the "target_resource" is always valid >> and points to the "iomem_resource" as arch_xen_unpopulated_init() is not >> implemented. So there won't be any fallback to use >> alloc_(free)_xenballooned_pages() here and fill_list() will behave as usual. > > If target_resource is always valid, then we don't need this special > check. In fact, the condition should never be true. The target_resource is always valid and points to the "iomem_resource" on x86 (this is equivalent to the behavior before this patch). On Arm target_resource might be NULL if arch_xen_unpopulated_init() failed, for example, if no extended regions reported by the hypervisor. We cannot use "iomem_resource" on Arm, only a resource constructed from extended regions. This is why I added that check (and fallback to xenballooned pages). What I was thinking is that in case of using old Xen (although we would need to balloon out RAM pages) we still would be able to keep working, so no need to disable CONFIG_XEN_UNPOPULATED_ALLOC on such setups. > > >> You raised a really good question, on Arm we need a fallback to balloon out >> RAM pages again if hypervisor doesn't provide extended regions (we run on old >> version, no unused regions with reasonable size, etc), so I decided to put a >> fallback code here, an indicator of the failure is invalid "target_resource". > I think it is unnecessary as we already assume today that > &iomem_resource is always available. >> I noticed the patch which is about to be upstreamed that removes >> alloc_(free)xenballooned_pages API [1]. Right now I have no idea how/where >> this fallback could be implemented as this is under build option control >> (CONFIG_XEN_UNPOPULATED_ALLOC). So the API with the same name is either used >> for unpopulated pages (if set) or ballooned pages (if not set). I would >> appreciate suggestions regarding that. I am wondering would it be possible and >> correctly to have both mechanisms (unpopulated and ballooned) enabled by >> default and some init code to decide which one to use at runtime or some sort? > I would keep it simple and remove the fallback from this patch. So: > > - if not CONFIG_XEN_UNPOPULATED_ALLOC, then balloon > - if CONFIG_XEN_UNPOPULATED_ALLOC, then > - xen_resource if present > - otherwise iomem_resource Unfortunately, we cannot use iomem_resource on Arm safely, either xen_resource or fail (if no fallback exists). > > The xen_resource/iomem_resource config can be done at init time using > target_resource. At runtime, target_resource is always != NULL so we > just go ahead and use it. Thank you for the suggestion. OK, let's keep it simple and drop fallback attempts for now. With one remark: We will make CONFIG_XEN_UNPOPULATED_ALLOC disabled by default on Arm in next patch. So by default everything will behave as usual on Arm (balloon out RAM pages), if user knows for sure that Xen reports extended regions, he/she can enable the config. This way we won't break anything. What do you think? [snip]
Juergen please see the bottom of the email On Fri, 19 Nov 2021, Oleksandr wrote: > On 19.11.21 02:59, Stefano Stabellini wrote: > > On Tue, 9 Nov 2021, Oleksandr wrote: > > > On 28.10.21 19:37, Stefano Stabellini wrote: > > > > > > Hi Stefano > > > > > > I am sorry for the late response. > > > > > > > On Tue, 26 Oct 2021, Oleksandr Tyshchenko wrote: > > > > > From: Oleksandr Tyshchenko <oleksandr_tyshchenko@epam.com> > > > > > > > > > > The main reason of this change is that unpopulated-alloc > > > > > code cannot be used in its current form on Arm, but there > > > > > is a desire to reuse it to avoid wasting real RAM pages > > > > > for the grant/foreign mappings. > > > > > > > > > > The problem is that system "iomem_resource" is used for > > > > > the address space allocation, but the really unallocated > > > > > space can't be figured out precisely by the domain on Arm > > > > > without hypervisor involvement. For example, not all device > > > > > I/O regions are known by the time domain starts creating > > > > > grant/foreign mappings. And following the advise from > > > > > "iomem_resource" we might end up reusing these regions by > > > > > a mistake. So, the hypervisor which maintains the P2M for > > > > > the domain is in the best position to provide unused regions > > > > > of guest physical address space which could be safely used > > > > > to create grant/foreign mappings. > > > > > > > > > > Introduce new helper arch_xen_unpopulated_init() which purpose > > > > > is to create specific Xen resource based on the memory regions > > > > > provided by the hypervisor to be used as unused space for Xen > > > > > scratch pages. > > > > > > > > > > If arch doesn't implement arch_xen_unpopulated_init() to > > > > > initialize Xen resource the default "iomem_resource" will be used. > > > > > So the behavior on x86 won't be changed. > > > > > > > > > > Also fall back to allocate xenballooned pages (steal real RAM > > > > > pages) if we do not have any suitable resource to work with and > > > > > as the result we won't be able to provide unpopulated pages. > > > > > > > > > > Signed-off-by: Oleksandr Tyshchenko <oleksandr_tyshchenko@epam.com> > > > > > --- > > > > > Changes RFC -> V2: > > > > > - new patch, instead of > > > > > "[RFC PATCH 2/2] xen/unpopulated-alloc: Query hypervisor to > > > > > provide > > > > > unallocated space" > > > > > --- > > > > > drivers/xen/unpopulated-alloc.c | 89 > > > > > +++++++++++++++++++++++++++++++++++++++-- > > > > > include/xen/xen.h | 2 + > > > > > 2 files changed, 88 insertions(+), 3 deletions(-) > > > > > > > > > > diff --git a/drivers/xen/unpopulated-alloc.c > > > > > b/drivers/xen/unpopulated-alloc.c > > > > > index a03dc5b..1f1d8d8 100644 > > > > > --- a/drivers/xen/unpopulated-alloc.c > > > > > +++ b/drivers/xen/unpopulated-alloc.c > > > > > @@ -8,6 +8,7 @@ > > > > > #include <asm/page.h> > > > > > +#include <xen/balloon.h> > > > > > #include <xen/page.h> > > > > > #include <xen/xen.h> > > > > > @@ -15,13 +16,29 @@ static DEFINE_MUTEX(list_lock); > > > > > static struct page *page_list; > > > > > static unsigned int list_count; > > > > > +static struct resource *target_resource; > > > > > +static struct resource xen_resource = { > > > > > + .name = "Xen unused space", > > > > > +}; > > > > > + > > > > > +/* > > > > > + * If arch is not happy with system "iomem_resource" being used for > > > > > + * the region allocation it can provide it's own view by initializing > > > > > + * "xen_resource" with unused regions of guest physical address space > > > > > + * provided by the hypervisor. > > > > > + */ > > > > > +int __weak arch_xen_unpopulated_init(struct resource *res) > > > > > +{ > > > > > + return -ENOSYS; > > > > > +} > > > > > + > > > > > static int fill_list(unsigned int nr_pages) > > > > > { > > > > > struct dev_pagemap *pgmap; > > > > > - struct resource *res; > > > > > + struct resource *res, *tmp_res = NULL; > > > > > void *vaddr; > > > > > unsigned int i, alloc_pages = round_up(nr_pages, > > > > > PAGES_PER_SECTION); > > > > > - int ret = -ENOMEM; > > > > > + int ret; > > > > > res = kzalloc(sizeof(*res), GFP_KERNEL); > > > > > if (!res) > > > > > @@ -30,7 +47,7 @@ static int fill_list(unsigned int nr_pages) > > > > > res->name = "Xen scratch"; > > > > > res->flags = IORESOURCE_MEM | IORESOURCE_BUSY; > > > > > - ret = allocate_resource(&iomem_resource, res, > > > > > + ret = allocate_resource(target_resource, res, > > > > > alloc_pages * PAGE_SIZE, 0, -1, > > > > > PAGES_PER_SECTION * PAGE_SIZE, NULL, > > > > > NULL); > > > > > if (ret < 0) { > > > > > @@ -38,6 +55,31 @@ static int fill_list(unsigned int nr_pages) > > > > > goto err_resource; > > > > > } > > > > > + /* > > > > > + * Reserve the region previously allocated from Xen resource > > > > > to avoid > > > > > + * re-using it by someone else. > > > > > + */ > > > > > + if (target_resource != &iomem_resource) { > > > > > + tmp_res = kzalloc(sizeof(*tmp_res), GFP_KERNEL); > > > > > + if (!res) { > > > > > + ret = -ENOMEM; > > > > > + goto err_insert; > > > > > + } > > > > > + > > > > > + tmp_res->name = res->name; > > > > > + tmp_res->start = res->start; > > > > > + tmp_res->end = res->end; > > > > > + tmp_res->flags = res->flags; > > > > > + > > > > > + ret = insert_resource(&iomem_resource, tmp_res); > > > > > + if (ret < 0) { > > > > > + pr_err("Cannot insert IOMEM resource [%llx - > > > > > %llx]\n", > > > > > + tmp_res->start, tmp_res->end); > > > > > + kfree(tmp_res); > > > > > + goto err_insert; > > > > > + } > > > > > + } > > > > I am a bit confused.. why do we need to do this? Who could be > > > > erroneously re-using the region? Are you saying that the next time > > > > allocate_resource is called it could find the same region again? It > > > > doesn't seem possible? > > > > > > No, as I understand the allocate_resource() being called for the same root > > > resource won't provide the same region... We only need to do this (insert > > > the > > > region into "iomem_resource") if we allocated it from our *internal* > > > "xen_resource", as *global* "iomem_resource" (which is used everywhere) is > > > not > > > aware of that region has been already allocated. So inserting a region > > > here we > > > reserving it, otherwise it could be reused elsewhere. > > But elsewhere where? > > I think, theoretically everywhere where allocate_resource(&iomem_resource, > ...) is called. > > > > Let's say that allocate_resource allocates a range from xen_resource. > > From reading the code, it doesn't look like iomem_resource would have > > that range because the extended regions described under /hypervisor are > > not added automatically to iomem_resource. > > > > So what if we don't call insert_resource? Nothing could allocate the > > same range because iomem_resource doesn't have it at all and > > xen_resource is not used anywhere if not here. > > > > What am I missing? > > > Below my understanding which, of course, might be wrong. > > If we don't claim resource by calling insert_resource (or even > request_resource) here then the same range could be allocated everywhere where > allocate_resource(&iomem_resource, ...) is called. > I don't see what prevents the same range from being allocated. Why actually > allocate_resource(&iomem_resource, ...) can't provide the same range if it is > free (not-reserved-yet) from it's PoV? The comment above allocate_resource() > says "allocate empty slot in the resource tree given range & alignment". So > this "empty slot" could be exactly the same range. > > I experimented with that a bit trying to call > allocate_resource(&iomem_resource, ...) several times in another place to see > what ranges it returns in both cases (w/ and w/o calling insert_resource > here). So an experiment confirmed (of course, if I made it correctly) that the > same range could be allocated if we didn't call insert_resource() here. And as > I understand there is nothing strange here, as iomem_resource covers all > address space initially (0, -1) and everything *not* inserted/requested (in > other words, reserved) yet is considered as free and could be provided if fits > constraints. Or I really missed something? Thanks for the explanation! It was me that didn't know that iomem_resource covers all the address space initially. I thought it was populated only with actual iomem ranges. Now it makes sense, thanks! > It feels to me that it would be better to call request_resource() instead of > insert_resource(). It seems, that if no conflict happens both functions will > behave in same way, but in case of conflict if the conflicting resource > entirely fit the new resource the former will return an error. I think, this > way we will be able to detect that a range we are trying to reserve is already > present and bail out early. > > > > > > Or maybe it is the other way around: core Linux code assumes everything > > is described in iomem_resource so something under kernel/ or mm/ would > > crash if we start using a page pointing to an address missing from > > iomem_resource? > > > > > > > pgmap = kzalloc(sizeof(*pgmap), GFP_KERNEL); > > > > > if (!pgmap) { > > > > > ret = -ENOMEM; > > > > > @@ -95,12 +137,40 @@ static int fill_list(unsigned int nr_pages) > > > > > err_memremap: > > > > > kfree(pgmap); > > > > > err_pgmap: > > > > > + if (tmp_res) { > > > > > + release_resource(tmp_res); > > > > > + kfree(tmp_res); > > > > > + } > > > > > +err_insert: > > > > > release_resource(res); > > > > > err_resource: > > > > > kfree(res); > > > > > return ret; > > > > > } > > > > > +static void unpopulated_init(void) > > > > > +{ > > > > > + static bool inited = false; > > > > initialized = false > > > ok. > > > > > > > > > > > > > > > + int ret; > > > > > + > > > > > + if (inited) > > > > > + return; > > > > > + > > > > > + /* > > > > > + * Try to initialize Xen resource the first and fall back to > > > > > default > > > > > + * resource if arch doesn't offer one. > > > > > + */ > > > > > + ret = arch_xen_unpopulated_init(&xen_resource); > > > > > + if (!ret) > > > > > + target_resource = &xen_resource; > > > > > + else if (ret == -ENOSYS) > > > > > + target_resource = &iomem_resource; > > > > > + else > > > > > + pr_err("Cannot initialize Xen resource\n"); > > > > > + > > > > > + inited = true; > > > > > +} > > > > Would it make sense to call unpopulated_init from an init function, > > > > rather than every time xen_alloc_unpopulated_pages is called? > > > Good point, thank you. Will do. To be honest, I also don't like the > > > current > > > approach much. > > > > > > > > > > > > > > > /** > > > > > * xen_alloc_unpopulated_pages - alloc unpopulated pages > > > > > * @nr_pages: Number of pages > > > > > @@ -112,6 +182,16 @@ int xen_alloc_unpopulated_pages(unsigned int > > > > > nr_pages, struct page **pages) > > > > > unsigned int i; > > > > > int ret = 0; > > > > > + unpopulated_init(); > > > > > + > > > > > + /* > > > > > + * Fall back to default behavior if we do not have any > > > > > suitable > > > > > resource > > > > > + * to allocate required region from and as the result we won't > > > > > be able > > > > > to > > > > > + * construct pages. > > > > > + */ > > > > > + if (!target_resource) > > > > > + return alloc_xenballooned_pages(nr_pages, pages); > > > > The commit message says that the behavior on x86 doesn't change but this > > > > seems to be a change that could impact x86? > > > I don't think, however I didn't tested on x86 and might be wrong, but > > > according to the current patch, on x86 the "target_resource" is always > > > valid > > > and points to the "iomem_resource" as arch_xen_unpopulated_init() is not > > > implemented. So there won't be any fallback to use > > > alloc_(free)_xenballooned_pages() here and fill_list() will behave as > > > usual. > > If target_resource is always valid, then we don't need this special > > check. In fact, the condition should never be true. > > > The target_resource is always valid and points to the "iomem_resource" on x86 > (this is equivalent to the behavior before this patch). > On Arm target_resource might be NULL if arch_xen_unpopulated_init() failed, > for example, if no extended regions reported by the hypervisor. > We cannot use "iomem_resource" on Arm, only a resource constructed from > extended regions. This is why I added that check (and fallback to xenballooned > pages). > What I was thinking is that in case of using old Xen (although we would need > to balloon out RAM pages) we still would be able to keep working, so no need > to disable CONFIG_XEN_UNPOPULATED_ALLOC on such setups. > > > > > You raised a really good question, on Arm we need a fallback to balloon > > > out > > > RAM pages again if hypervisor doesn't provide extended regions (we run on > > > old > > > version, no unused regions with reasonable size, etc), so I decided to put > > > a > > > fallback code here, an indicator of the failure is invalid > > > "target_resource". > > I think it is unnecessary as we already assume today that > > &iomem_resource is always available. > > > I noticed the patch which is about to be upstreamed that removes > > > alloc_(free)xenballooned_pages API [1]. Right now I have no idea how/where > > > this fallback could be implemented as this is under build option control > > > (CONFIG_XEN_UNPOPULATED_ALLOC). So the API with the same name is either > > > used > > > for unpopulated pages (if set) or ballooned pages (if not set). I would > > > appreciate suggestions regarding that. I am wondering would it be possible > > > and > > > correctly to have both mechanisms (unpopulated and ballooned) enabled by > > > default and some init code to decide which one to use at runtime or some > > > sort? > > I would keep it simple and remove the fallback from this patch. So: > > > > - if not CONFIG_XEN_UNPOPULATED_ALLOC, then balloon > > - if CONFIG_XEN_UNPOPULATED_ALLOC, then > > - xen_resource if present > > - otherwise iomem_resource > > Unfortunately, we cannot use iomem_resource on Arm safely, either xen_resource > or fail (if no fallback exists). > > > > > > The xen_resource/iomem_resource config can be done at init time using > > target_resource. At runtime, target_resource is always != NULL so we > > just go ahead and use it. > > > Thank you for the suggestion. OK, let's keep it simple and drop fallback > attempts for now. With one remark: > We will make CONFIG_XEN_UNPOPULATED_ALLOC disabled by default on Arm in next > patch. So by default everything will behave as usual on Arm (balloon out RAM > pages), > if user knows for sure that Xen reports extended regions, he/she can enable > the config. This way we won't break anything. What do you think? Actually after reading your replies and explanation I changed opinion: I think we do need the fallback because Linux cannot really assume that it is running on "new Xen" so it definitely needs to keep working if CONFIG_XEN_UNPOPULATED_ALLOC is enabled and the extended regions are not advertised. I think we'll have to roll back some of the changes introduced by 121f2faca2c0a. That's because even if CONFIG_XEN_UNPOPULATED_ALLOC is enabled we cannot know if we can use unpopulated-alloc or whether we have to use alloc_xenballooned_pages until we parse the /hypervisor node in device tree at runtime. In short, we cannot switch between unpopulated-alloc and alloc_xenballooned_pages at build time, we have to do it at runtime (boot time). Juergen, what do you think?
On 20.11.21 04:19, Stefano Stabellini wrote: Hi Stefano, Juergen, all > Juergen please see the bottom of the email > > On Fri, 19 Nov 2021, Oleksandr wrote: >> On 19.11.21 02:59, Stefano Stabellini wrote: >>> On Tue, 9 Nov 2021, Oleksandr wrote: >>>> On 28.10.21 19:37, Stefano Stabellini wrote: >>>> >>>> Hi Stefano >>>> >>>> I am sorry for the late response. >>>> >>>>> On Tue, 26 Oct 2021, Oleksandr Tyshchenko wrote: >>>>>> From: Oleksandr Tyshchenko <oleksandr_tyshchenko@epam.com> >>>>>> >>>>>> The main reason of this change is that unpopulated-alloc >>>>>> code cannot be used in its current form on Arm, but there >>>>>> is a desire to reuse it to avoid wasting real RAM pages >>>>>> for the grant/foreign mappings. >>>>>> >>>>>> The problem is that system "iomem_resource" is used for >>>>>> the address space allocation, but the really unallocated >>>>>> space can't be figured out precisely by the domain on Arm >>>>>> without hypervisor involvement. For example, not all device >>>>>> I/O regions are known by the time domain starts creating >>>>>> grant/foreign mappings. And following the advise from >>>>>> "iomem_resource" we might end up reusing these regions by >>>>>> a mistake. So, the hypervisor which maintains the P2M for >>>>>> the domain is in the best position to provide unused regions >>>>>> of guest physical address space which could be safely used >>>>>> to create grant/foreign mappings. >>>>>> >>>>>> Introduce new helper arch_xen_unpopulated_init() which purpose >>>>>> is to create specific Xen resource based on the memory regions >>>>>> provided by the hypervisor to be used as unused space for Xen >>>>>> scratch pages. >>>>>> >>>>>> If arch doesn't implement arch_xen_unpopulated_init() to >>>>>> initialize Xen resource the default "iomem_resource" will be used. >>>>>> So the behavior on x86 won't be changed. >>>>>> >>>>>> Also fall back to allocate xenballooned pages (steal real RAM >>>>>> pages) if we do not have any suitable resource to work with and >>>>>> as the result we won't be able to provide unpopulated pages. >>>>>> >>>>>> Signed-off-by: Oleksandr Tyshchenko <oleksandr_tyshchenko@epam.com> >>>>>> --- >>>>>> Changes RFC -> V2: >>>>>> - new patch, instead of >>>>>> "[RFC PATCH 2/2] xen/unpopulated-alloc: Query hypervisor to >>>>>> provide >>>>>> unallocated space" >>>>>> --- >>>>>> drivers/xen/unpopulated-alloc.c | 89 >>>>>> +++++++++++++++++++++++++++++++++++++++-- >>>>>> include/xen/xen.h | 2 + >>>>>> 2 files changed, 88 insertions(+), 3 deletions(-) >>>>>> >>>>>> diff --git a/drivers/xen/unpopulated-alloc.c >>>>>> b/drivers/xen/unpopulated-alloc.c >>>>>> index a03dc5b..1f1d8d8 100644 >>>>>> --- a/drivers/xen/unpopulated-alloc.c >>>>>> +++ b/drivers/xen/unpopulated-alloc.c >>>>>> @@ -8,6 +8,7 @@ >>>>>> #include <asm/page.h> >>>>>> +#include <xen/balloon.h> >>>>>> #include <xen/page.h> >>>>>> #include <xen/xen.h> >>>>>> @@ -15,13 +16,29 @@ static DEFINE_MUTEX(list_lock); >>>>>> static struct page *page_list; >>>>>> static unsigned int list_count; >>>>>> +static struct resource *target_resource; >>>>>> +static struct resource xen_resource = { >>>>>> + .name = "Xen unused space", >>>>>> +}; >>>>>> + >>>>>> +/* >>>>>> + * If arch is not happy with system "iomem_resource" being used for >>>>>> + * the region allocation it can provide it's own view by initializing >>>>>> + * "xen_resource" with unused regions of guest physical address space >>>>>> + * provided by the hypervisor. >>>>>> + */ >>>>>> +int __weak arch_xen_unpopulated_init(struct resource *res) >>>>>> +{ >>>>>> + return -ENOSYS; >>>>>> +} >>>>>> + >>>>>> static int fill_list(unsigned int nr_pages) >>>>>> { >>>>>> struct dev_pagemap *pgmap; >>>>>> - struct resource *res; >>>>>> + struct resource *res, *tmp_res = NULL; >>>>>> void *vaddr; >>>>>> unsigned int i, alloc_pages = round_up(nr_pages, >>>>>> PAGES_PER_SECTION); >>>>>> - int ret = -ENOMEM; >>>>>> + int ret; >>>>>> res = kzalloc(sizeof(*res), GFP_KERNEL); >>>>>> if (!res) >>>>>> @@ -30,7 +47,7 @@ static int fill_list(unsigned int nr_pages) >>>>>> res->name = "Xen scratch"; >>>>>> res->flags = IORESOURCE_MEM | IORESOURCE_BUSY; >>>>>> - ret = allocate_resource(&iomem_resource, res, >>>>>> + ret = allocate_resource(target_resource, res, >>>>>> alloc_pages * PAGE_SIZE, 0, -1, >>>>>> PAGES_PER_SECTION * PAGE_SIZE, NULL, >>>>>> NULL); >>>>>> if (ret < 0) { >>>>>> @@ -38,6 +55,31 @@ static int fill_list(unsigned int nr_pages) >>>>>> goto err_resource; >>>>>> } >>>>>> + /* >>>>>> + * Reserve the region previously allocated from Xen resource >>>>>> to avoid >>>>>> + * re-using it by someone else. >>>>>> + */ >>>>>> + if (target_resource != &iomem_resource) { >>>>>> + tmp_res = kzalloc(sizeof(*tmp_res), GFP_KERNEL); >>>>>> + if (!res) { >>>>>> + ret = -ENOMEM; >>>>>> + goto err_insert; >>>>>> + } >>>>>> + >>>>>> + tmp_res->name = res->name; >>>>>> + tmp_res->start = res->start; >>>>>> + tmp_res->end = res->end; >>>>>> + tmp_res->flags = res->flags; >>>>>> + >>>>>> + ret = insert_resource(&iomem_resource, tmp_res); >>>>>> + if (ret < 0) { >>>>>> + pr_err("Cannot insert IOMEM resource [%llx - >>>>>> %llx]\n", >>>>>> + tmp_res->start, tmp_res->end); >>>>>> + kfree(tmp_res); >>>>>> + goto err_insert; >>>>>> + } >>>>>> + } >>>>> I am a bit confused.. why do we need to do this? Who could be >>>>> erroneously re-using the region? Are you saying that the next time >>>>> allocate_resource is called it could find the same region again? It >>>>> doesn't seem possible? >>>> No, as I understand the allocate_resource() being called for the same root >>>> resource won't provide the same region... We only need to do this (insert >>>> the >>>> region into "iomem_resource") if we allocated it from our *internal* >>>> "xen_resource", as *global* "iomem_resource" (which is used everywhere) is >>>> not >>>> aware of that region has been already allocated. So inserting a region >>>> here we >>>> reserving it, otherwise it could be reused elsewhere. >>> But elsewhere where? >> I think, theoretically everywhere where allocate_resource(&iomem_resource, >> ...) is called. >> >> >>> Let's say that allocate_resource allocates a range from xen_resource. >>> From reading the code, it doesn't look like iomem_resource would have >>> that range because the extended regions described under /hypervisor are >>> not added automatically to iomem_resource. >>> >>> So what if we don't call insert_resource? Nothing could allocate the >>> same range because iomem_resource doesn't have it at all and >>> xen_resource is not used anywhere if not here. >>> >>> What am I missing? >> >> Below my understanding which, of course, might be wrong. >> >> If we don't claim resource by calling insert_resource (or even >> request_resource) here then the same range could be allocated everywhere where >> allocate_resource(&iomem_resource, ...) is called. >> I don't see what prevents the same range from being allocated. Why actually >> allocate_resource(&iomem_resource, ...) can't provide the same range if it is >> free (not-reserved-yet) from it's PoV? The comment above allocate_resource() >> says "allocate empty slot in the resource tree given range & alignment". So >> this "empty slot" could be exactly the same range. >> >> I experimented with that a bit trying to call >> allocate_resource(&iomem_resource, ...) several times in another place to see >> what ranges it returns in both cases (w/ and w/o calling insert_resource >> here). So an experiment confirmed (of course, if I made it correctly) that the >> same range could be allocated if we didn't call insert_resource() here. And as >> I understand there is nothing strange here, as iomem_resource covers all >> address space initially (0, -1) and everything *not* inserted/requested (in >> other words, reserved) yet is considered as free and could be provided if fits >> constraints. Or I really missed something? > Thanks for the explanation! It was me that didn't know that > iomem_resource covers all the address space initially. I thought it was > populated only with actual iomem ranges. Now it makes sense, thanks! > > >> It feels to me that it would be better to call request_resource() instead of >> insert_resource(). It seems, that if no conflict happens both functions will >> behave in same way, but in case of conflict if the conflicting resource >> entirely fit the new resource the former will return an error. I think, this >> way we will be able to detect that a range we are trying to reserve is already >> present and bail out early. >> >> >>> Or maybe it is the other way around: core Linux code assumes everything >>> is described in iomem_resource so something under kernel/ or mm/ would >>> crash if we start using a page pointing to an address missing from >>> iomem_resource? >>> >>>>>> pgmap = kzalloc(sizeof(*pgmap), GFP_KERNEL); >>>>>> if (!pgmap) { >>>>>> ret = -ENOMEM; >>>>>> @@ -95,12 +137,40 @@ static int fill_list(unsigned int nr_pages) >>>>>> err_memremap: >>>>>> kfree(pgmap); >>>>>> err_pgmap: >>>>>> + if (tmp_res) { >>>>>> + release_resource(tmp_res); >>>>>> + kfree(tmp_res); >>>>>> + } >>>>>> +err_insert: >>>>>> release_resource(res); >>>>>> err_resource: >>>>>> kfree(res); >>>>>> return ret; >>>>>> } >>>>>> +static void unpopulated_init(void) >>>>>> +{ >>>>>> + static bool inited = false; >>>>> initialized = false >>>> ok. >>>> >>>> >>>>>> + int ret; >>>>>> + >>>>>> + if (inited) >>>>>> + return; >>>>>> + >>>>>> + /* >>>>>> + * Try to initialize Xen resource the first and fall back to >>>>>> default >>>>>> + * resource if arch doesn't offer one. >>>>>> + */ >>>>>> + ret = arch_xen_unpopulated_init(&xen_resource); >>>>>> + if (!ret) >>>>>> + target_resource = &xen_resource; >>>>>> + else if (ret == -ENOSYS) >>>>>> + target_resource = &iomem_resource; >>>>>> + else >>>>>> + pr_err("Cannot initialize Xen resource\n"); >>>>>> + >>>>>> + inited = true; >>>>>> +} >>>>> Would it make sense to call unpopulated_init from an init function, >>>>> rather than every time xen_alloc_unpopulated_pages is called? >>>> Good point, thank you. Will do. To be honest, I also don't like the >>>> current >>>> approach much. >>>> >>>> >>>>>> /** >>>>>> * xen_alloc_unpopulated_pages - alloc unpopulated pages >>>>>> * @nr_pages: Number of pages >>>>>> @@ -112,6 +182,16 @@ int xen_alloc_unpopulated_pages(unsigned int >>>>>> nr_pages, struct page **pages) >>>>>> unsigned int i; >>>>>> int ret = 0; >>>>>> + unpopulated_init(); >>>>>> + >>>>>> + /* >>>>>> + * Fall back to default behavior if we do not have any >>>>>> suitable >>>>>> resource >>>>>> + * to allocate required region from and as the result we won't >>>>>> be able >>>>>> to >>>>>> + * construct pages. >>>>>> + */ >>>>>> + if (!target_resource) >>>>>> + return alloc_xenballooned_pages(nr_pages, pages); >>>>> The commit message says that the behavior on x86 doesn't change but this >>>>> seems to be a change that could impact x86? >>>> I don't think, however I didn't tested on x86 and might be wrong, but >>>> according to the current patch, on x86 the "target_resource" is always >>>> valid >>>> and points to the "iomem_resource" as arch_xen_unpopulated_init() is not >>>> implemented. So there won't be any fallback to use >>>> alloc_(free)_xenballooned_pages() here and fill_list() will behave as >>>> usual. >>> If target_resource is always valid, then we don't need this special >>> check. In fact, the condition should never be true. >> >> The target_resource is always valid and points to the "iomem_resource" on x86 >> (this is equivalent to the behavior before this patch). >> On Arm target_resource might be NULL if arch_xen_unpopulated_init() failed, >> for example, if no extended regions reported by the hypervisor. >> We cannot use "iomem_resource" on Arm, only a resource constructed from >> extended regions. This is why I added that check (and fallback to xenballooned >> pages). >> What I was thinking is that in case of using old Xen (although we would need >> to balloon out RAM pages) we still would be able to keep working, so no need >> to disable CONFIG_XEN_UNPOPULATED_ALLOC on such setups. >> >> >>>> You raised a really good question, on Arm we need a fallback to balloon >>>> out >>>> RAM pages again if hypervisor doesn't provide extended regions (we run on >>>> old >>>> version, no unused regions with reasonable size, etc), so I decided to put >>>> a >>>> fallback code here, an indicator of the failure is invalid >>>> "target_resource". >>> I think it is unnecessary as we already assume today that >>> &iomem_resource is always available. >>>> I noticed the patch which is about to be upstreamed that removes >>>> alloc_(free)xenballooned_pages API [1]. Right now I have no idea how/where >>>> this fallback could be implemented as this is under build option control >>>> (CONFIG_XEN_UNPOPULATED_ALLOC). So the API with the same name is either >>>> used >>>> for unpopulated pages (if set) or ballooned pages (if not set). I would >>>> appreciate suggestions regarding that. I am wondering would it be possible >>>> and >>>> correctly to have both mechanisms (unpopulated and ballooned) enabled by >>>> default and some init code to decide which one to use at runtime or some >>>> sort? >>> I would keep it simple and remove the fallback from this patch. So: >>> >>> - if not CONFIG_XEN_UNPOPULATED_ALLOC, then balloon >>> - if CONFIG_XEN_UNPOPULATED_ALLOC, then >>> - xen_resource if present >>> - otherwise iomem_resource >> Unfortunately, we cannot use iomem_resource on Arm safely, either xen_resource >> or fail (if no fallback exists). >> >> >>> The xen_resource/iomem_resource config can be done at init time using >>> target_resource. At runtime, target_resource is always != NULL so we >>> just go ahead and use it. >> >> Thank you for the suggestion. OK, let's keep it simple and drop fallback >> attempts for now. With one remark: >> We will make CONFIG_XEN_UNPOPULATED_ALLOC disabled by default on Arm in next >> patch. So by default everything will behave as usual on Arm (balloon out RAM >> pages), >> if user knows for sure that Xen reports extended regions, he/she can enable >> the config. This way we won't break anything. What do you think? > Actually after reading your replies and explanation I changed opinion: I > think we do need the fallback because Linux cannot really assume that > it is running on "new Xen" so it definitely needs to keep working if > CONFIG_XEN_UNPOPULATED_ALLOC is enabled and the extended regions are not > advertised. > > I think we'll have to roll back some of the changes introduced by > 121f2faca2c0a. That's because even if CONFIG_XEN_UNPOPULATED_ALLOC is > enabled we cannot know if we can use unpopulated-alloc or whether we > have to use alloc_xenballooned_pages until we parse the /hypervisor node > in device tree at runtime. Exactly! > > In short, we cannot switch between unpopulated-alloc and > alloc_xenballooned_pages at build time, we have to do it at runtime > (boot time). +1 I created a patch to partially revert 121f2faca2c0a "xen/balloon: rename alloc/free_xenballooned_pages". If there is no objections I will add it to V3 (which is almost ready, except the fallback bits). Could you please tell me what do you think? From dc79bcd425358596d95e715a8bd8b81deaaeb703 Mon Sep 17 00:00:00 2001 From: Oleksandr Tyshchenko <oleksandr_tyshchenko@epam.com> Date: Tue, 23 Nov 2021 18:14:41 +0200 Subject: [PATCH] xen/balloon: Bring alloc(free)_xenballooned_pages helpers back This patch rolls back some of the changes introduced by commit 121f2faca2c0a "xen/balloon: rename alloc/free_xenballooned_pages" in order to make possible to still allocate xenballooned pages if CONFIG_XEN_UNPOPULATED_ALLOC is enabled. On Arm the unpopulated pages will be allocated on top of extended regions provided by Xen via device-tree (the subsequent patches will add required bits to support unpopulated-alloc feature on Arm). The problem is that extended regions feature has been introduced into Xen quite recently (during 4.16 release cycle). So this effectively means that Linux must only use unpopulated-alloc on Arm if it is running on "new Xen" which advertises these regions. But, it will only be known after parsing the "hypervisor" node at boot time, so before doing that we cannot assume anything. In order to keep working if CONFIG_XEN_UNPOPULATED_ALLOC is enabled and the extended regions are not advertised (Linux is running on "old Xen", etc) we need the fallback to alloc_xenballooned_pages(). This way we wouldn't reduce the amount of memory usable (wasting RAM pages) for any of the external mappings anymore (and eliminate XSA-300) with "new Xen", but would be still functional ballooning out RAM pages with "old Xen". Also rename alloc(free)_xenballooned_pages to xen_alloc(free)_ballooned_pages. Signed-off-by: Oleksandr Tyshchenko <oleksandr_tyshchenko@epam.com> --- drivers/xen/balloon.c | 20 +++++++++----------- include/xen/balloon.h | 3 +++ include/xen/xen.h | 6 ++++++ 3 files changed, 18 insertions(+), 11 deletions(-) diff --git a/drivers/xen/balloon.c b/drivers/xen/balloon.c index ba2ea11..a2c4fc49 100644 --- a/drivers/xen/balloon.c +++ b/drivers/xen/balloon.c @@ -581,7 +581,6 @@ void balloon_set_new_target(unsigned long target) } EXPORT_SYMBOL_GPL(balloon_set_new_target); -#ifndef CONFIG_XEN_UNPOPULATED_ALLOC static int add_ballooned_pages(unsigned int nr_pages) { enum bp_state st; @@ -610,12 +609,12 @@ static int add_ballooned_pages(unsigned int nr_pages) } /** - * xen_alloc_unpopulated_pages - get pages that have been ballooned out + * xen_alloc_ballooned_pages - get pages that have been ballooned out * @nr_pages: Number of pages to get * @pages: pages returned * @return 0 on success, error otherwise */ -int xen_alloc_unpopulated_pages(unsigned int nr_pages, struct page **pages) +int xen_alloc_ballooned_pages(unsigned int nr_pages, struct page **pages) { unsigned int pgno = 0; struct page *page; @@ -652,23 +651,23 @@ int xen_alloc_unpopulated_pages(unsigned int nr_pages, struct page **pages) return 0; out_undo: mutex_unlock(&balloon_mutex); - xen_free_unpopulated_pages(pgno, pages); + xen_free_ballooned_pages(pgno, pages); /* - * NB: free_xenballooned_pages will only subtract pgno pages, but since + * NB: xen_free_ballooned_pages will only subtract pgno pages, but since * target_unpopulated is incremented with nr_pages at the start we need * to remove the remaining ones also, or accounting will be screwed. */ balloon_stats.target_unpopulated -= nr_pages - pgno; return ret; } -EXPORT_SYMBOL(xen_alloc_unpopulated_pages); +EXPORT_SYMBOL(xen_alloc_ballooned_pages); /** - * xen_free_unpopulated_pages - return pages retrieved with get_ballooned_pages + * xen_free_ballooned_pages - return pages retrieved with get_ballooned_pages * @nr_pages: Number of pages * @pages: pages to return */ -void xen_free_unpopulated_pages(unsigned int nr_pages, struct page **pages) +void xen_free_ballooned_pages(unsigned int nr_pages, struct page **pages) { unsigned int i; @@ -687,9 +686,9 @@ void xen_free_unpopulated_pages(unsigned int nr_pages, struct page **pages) mutex_unlock(&balloon_mutex); } -EXPORT_SYMBOL(xen_free_unpopulated_pages); +EXPORT_SYMBOL(xen_free_ballooned_pages); -#if defined(CONFIG_XEN_PV) +#if defined(CONFIG_XEN_PV) && !defined(CONFIG_XEN_UNPOPULATED_ALLOC) static void __init balloon_add_region(unsigned long start_pfn, unsigned long pages) { @@ -712,7 +711,6 @@ static void __init balloon_add_region(unsigned long start_pfn, balloon_stats.total_pages += extra_pfn_end - start_pfn; } #endif -#endif static int __init balloon_init(void) { diff --git a/include/xen/balloon.h b/include/xen/balloon.h index e93d4f0..f78a6cc 100644 --- a/include/xen/balloon.h +++ b/include/xen/balloon.h @@ -26,6 +26,9 @@ extern struct balloon_stats balloon_stats; void balloon_set_new_target(unsigned long target); +int xen_alloc_ballooned_pages(unsigned int nr_pages, struct page **pages); +void xen_free_ballooned_pages(unsigned int nr_pages, struct page **pages); + #ifdef CONFIG_XEN_BALLOON void xen_balloon_init(void); #else diff --git a/include/xen/xen.h b/include/xen/xen.h index 9f031b5..410e3e4 100644 --- a/include/xen/xen.h +++ b/include/xen/xen.h @@ -52,7 +52,13 @@ bool xen_biovec_phys_mergeable(const struct bio_vec *vec1, extern u64 xen_saved_max_mem_size; #endif +#ifdef CONFIG_XEN_UNPOPULATED_ALLOC int xen_alloc_unpopulated_pages(unsigned int nr_pages, struct page **pages); void xen_free_unpopulated_pages(unsigned int nr_pages, struct page **pages); +#else +#define xen_alloc_unpopulated_pages xen_alloc_ballooned_pages +#define xen_free_unpopulated_pages xen_free_ballooned_pages +#include <xen/balloon.h> +#endif #endif /* _XEN_XEN_H */
On Tue, 23 Nov 2021, Oleksandr wrote: > > Actually after reading your replies and explanation I changed opinion: I > > think we do need the fallback because Linux cannot really assume that > > it is running on "new Xen" so it definitely needs to keep working if > > CONFIG_XEN_UNPOPULATED_ALLOC is enabled and the extended regions are not > > advertised. > > > > I think we'll have to roll back some of the changes introduced by > > 121f2faca2c0a. That's because even if CONFIG_XEN_UNPOPULATED_ALLOC is > > enabled we cannot know if we can use unpopulated-alloc or whether we > > have to use alloc_xenballooned_pages until we parse the /hypervisor node > > in device tree at runtime. > > Exactly! > > > > > > In short, we cannot switch between unpopulated-alloc and > > alloc_xenballooned_pages at build time, we have to do it at runtime > > (boot time). > > +1 > > > I created a patch to partially revert 121f2faca2c0a "xen/balloon: rename > alloc/free_xenballooned_pages". > > If there is no objections I will add it to V3 (which is almost ready, except > the fallback bits). Could you please tell me what do you think? It makes sense to me. You can add my Reviewed-by. > From dc79bcd425358596d95e715a8bd8b81deaaeb703 Mon Sep 17 00:00:00 2001 > From: Oleksandr Tyshchenko <oleksandr_tyshchenko@epam.com> > Date: Tue, 23 Nov 2021 18:14:41 +0200 > Subject: [PATCH] xen/balloon: Bring alloc(free)_xenballooned_pages helpers > back > > This patch rolls back some of the changes introduced by commit > 121f2faca2c0a "xen/balloon: rename alloc/free_xenballooned_pages" > in order to make possible to still allocate xenballooned pages > if CONFIG_XEN_UNPOPULATED_ALLOC is enabled. > > On Arm the unpopulated pages will be allocated on top of extended > regions provided by Xen via device-tree (the subsequent patches > will add required bits to support unpopulated-alloc feature on Arm). > The problem is that extended regions feature has been introduced > into Xen quite recently (during 4.16 release cycle). So this > effectively means that Linux must only use unpopulated-alloc on Arm > if it is running on "new Xen" which advertises these regions. > But, it will only be known after parsing the "hypervisor" node > at boot time, so before doing that we cannot assume anything. > > In order to keep working if CONFIG_XEN_UNPOPULATED_ALLOC is enabled > and the extended regions are not advertised (Linux is running on > "old Xen", etc) we need the fallback to alloc_xenballooned_pages(). > > This way we wouldn't reduce the amount of memory usable (wasting > RAM pages) for any of the external mappings anymore (and eliminate > XSA-300) with "new Xen", but would be still functional ballooning > out RAM pages with "old Xen". > > Also rename alloc(free)_xenballooned_pages to xen_alloc(free)_ballooned_pages. > > Signed-off-by: Oleksandr Tyshchenko <oleksandr_tyshchenko@epam.com> > --- > drivers/xen/balloon.c | 20 +++++++++----------- > include/xen/balloon.h | 3 +++ > include/xen/xen.h | 6 ++++++ > 3 files changed, 18 insertions(+), 11 deletions(-) > > diff --git a/drivers/xen/balloon.c b/drivers/xen/balloon.c > index ba2ea11..a2c4fc49 100644 > --- a/drivers/xen/balloon.c > +++ b/drivers/xen/balloon.c > @@ -581,7 +581,6 @@ void balloon_set_new_target(unsigned long target) > } > EXPORT_SYMBOL_GPL(balloon_set_new_target); > > -#ifndef CONFIG_XEN_UNPOPULATED_ALLOC > static int add_ballooned_pages(unsigned int nr_pages) > { > enum bp_state st; > @@ -610,12 +609,12 @@ static int add_ballooned_pages(unsigned int nr_pages) > } > > /** > - * xen_alloc_unpopulated_pages - get pages that have been ballooned out > + * xen_alloc_ballooned_pages - get pages that have been ballooned out > * @nr_pages: Number of pages to get > * @pages: pages returned > * @return 0 on success, error otherwise > */ > -int xen_alloc_unpopulated_pages(unsigned int nr_pages, struct page **pages) > +int xen_alloc_ballooned_pages(unsigned int nr_pages, struct page **pages) > { > unsigned int pgno = 0; > struct page *page; > @@ -652,23 +651,23 @@ int xen_alloc_unpopulated_pages(unsigned int nr_pages, > struct page **pages) > return 0; > out_undo: > mutex_unlock(&balloon_mutex); > - xen_free_unpopulated_pages(pgno, pages); > + xen_free_ballooned_pages(pgno, pages); > /* > - * NB: free_xenballooned_pages will only subtract pgno pages, but since > + * NB: xen_free_ballooned_pages will only subtract pgno pages, but since > * target_unpopulated is incremented with nr_pages at the start we need > * to remove the remaining ones also, or accounting will be screwed. > */ > balloon_stats.target_unpopulated -= nr_pages - pgno; > return ret; > } > -EXPORT_SYMBOL(xen_alloc_unpopulated_pages); > +EXPORT_SYMBOL(xen_alloc_ballooned_pages); > > /** > - * xen_free_unpopulated_pages - return pages retrieved with > get_ballooned_pages > + * xen_free_ballooned_pages - return pages retrieved with get_ballooned_pages > * @nr_pages: Number of pages > * @pages: pages to return > */ > -void xen_free_unpopulated_pages(unsigned int nr_pages, struct page **pages) > +void xen_free_ballooned_pages(unsigned int nr_pages, struct page **pages) > { > unsigned int i; > > @@ -687,9 +686,9 @@ void xen_free_unpopulated_pages(unsigned int nr_pages, > struct page **pages) > > mutex_unlock(&balloon_mutex); > } > -EXPORT_SYMBOL(xen_free_unpopulated_pages); > +EXPORT_SYMBOL(xen_free_ballooned_pages); > > -#if defined(CONFIG_XEN_PV) > +#if defined(CONFIG_XEN_PV) && !defined(CONFIG_XEN_UNPOPULATED_ALLOC) > static void __init balloon_add_region(unsigned long start_pfn, > unsigned long pages) > { > @@ -712,7 +711,6 @@ static void __init balloon_add_region(unsigned long > start_pfn, > balloon_stats.total_pages += extra_pfn_end - start_pfn; > } > #endif > -#endif > > static int __init balloon_init(void) > { > diff --git a/include/xen/balloon.h b/include/xen/balloon.h > index e93d4f0..f78a6cc 100644 > --- a/include/xen/balloon.h > +++ b/include/xen/balloon.h > @@ -26,6 +26,9 @@ extern struct balloon_stats balloon_stats; > > void balloon_set_new_target(unsigned long target); > > +int xen_alloc_ballooned_pages(unsigned int nr_pages, struct page **pages); > +void xen_free_ballooned_pages(unsigned int nr_pages, struct page **pages); > + > #ifdef CONFIG_XEN_BALLOON > void xen_balloon_init(void); > #else > diff --git a/include/xen/xen.h b/include/xen/xen.h > index 9f031b5..410e3e4 100644 > --- a/include/xen/xen.h > +++ b/include/xen/xen.h > @@ -52,7 +52,13 @@ bool xen_biovec_phys_mergeable(const struct bio_vec *vec1, > extern u64 xen_saved_max_mem_size; > #endif > > +#ifdef CONFIG_XEN_UNPOPULATED_ALLOC > int xen_alloc_unpopulated_pages(unsigned int nr_pages, struct page **pages); > void xen_free_unpopulated_pages(unsigned int nr_pages, struct page **pages); > +#else > +#define xen_alloc_unpopulated_pages xen_alloc_ballooned_pages > +#define xen_free_unpopulated_pages xen_free_ballooned_pages > +#include <xen/balloon.h> > +#endif > > #endif /* _XEN_XEN_H */
On 23.11.21 17:46, Oleksandr wrote: > > On 20.11.21 04:19, Stefano Stabellini wrote: > > Hi Stefano, Juergen, all > > >> Juergen please see the bottom of the email >> >> On Fri, 19 Nov 2021, Oleksandr wrote: >>> On 19.11.21 02:59, Stefano Stabellini wrote: >>>> On Tue, 9 Nov 2021, Oleksandr wrote: >>>>> On 28.10.21 19:37, Stefano Stabellini wrote: >>>>> >>>>> Hi Stefano >>>>> >>>>> I am sorry for the late response. >>>>> >>>>>> On Tue, 26 Oct 2021, Oleksandr Tyshchenko wrote: >>>>>>> From: Oleksandr Tyshchenko <oleksandr_tyshchenko@epam.com> >>>>>>> >>>>>>> The main reason of this change is that unpopulated-alloc >>>>>>> code cannot be used in its current form on Arm, but there >>>>>>> is a desire to reuse it to avoid wasting real RAM pages >>>>>>> for the grant/foreign mappings. >>>>>>> >>>>>>> The problem is that system "iomem_resource" is used for >>>>>>> the address space allocation, but the really unallocated >>>>>>> space can't be figured out precisely by the domain on Arm >>>>>>> without hypervisor involvement. For example, not all device >>>>>>> I/O regions are known by the time domain starts creating >>>>>>> grant/foreign mappings. And following the advise from >>>>>>> "iomem_resource" we might end up reusing these regions by >>>>>>> a mistake. So, the hypervisor which maintains the P2M for >>>>>>> the domain is in the best position to provide unused regions >>>>>>> of guest physical address space which could be safely used >>>>>>> to create grant/foreign mappings. >>>>>>> >>>>>>> Introduce new helper arch_xen_unpopulated_init() which purpose >>>>>>> is to create specific Xen resource based on the memory regions >>>>>>> provided by the hypervisor to be used as unused space for Xen >>>>>>> scratch pages. >>>>>>> >>>>>>> If arch doesn't implement arch_xen_unpopulated_init() to >>>>>>> initialize Xen resource the default "iomem_resource" will be used. >>>>>>> So the behavior on x86 won't be changed. >>>>>>> >>>>>>> Also fall back to allocate xenballooned pages (steal real RAM >>>>>>> pages) if we do not have any suitable resource to work with and >>>>>>> as the result we won't be able to provide unpopulated pages. >>>>>>> >>>>>>> Signed-off-by: Oleksandr Tyshchenko <oleksandr_tyshchenko@epam.com> >>>>>>> --- >>>>>>> Changes RFC -> V2: >>>>>>> - new patch, instead of >>>>>>> "[RFC PATCH 2/2] xen/unpopulated-alloc: Query hypervisor to >>>>>>> provide >>>>>>> unallocated space" >>>>>>> --- >>>>>>> drivers/xen/unpopulated-alloc.c | 89 >>>>>>> +++++++++++++++++++++++++++++++++++++++-- >>>>>>> include/xen/xen.h | 2 + >>>>>>> 2 files changed, 88 insertions(+), 3 deletions(-) >>>>>>> >>>>>>> diff --git a/drivers/xen/unpopulated-alloc.c >>>>>>> b/drivers/xen/unpopulated-alloc.c >>>>>>> index a03dc5b..1f1d8d8 100644 >>>>>>> --- a/drivers/xen/unpopulated-alloc.c >>>>>>> +++ b/drivers/xen/unpopulated-alloc.c >>>>>>> @@ -8,6 +8,7 @@ >>>>>>> #include <asm/page.h> >>>>>>> +#include <xen/balloon.h> >>>>>>> #include <xen/page.h> >>>>>>> #include <xen/xen.h> >>>>>>> @@ -15,13 +16,29 @@ static DEFINE_MUTEX(list_lock); >>>>>>> static struct page *page_list; >>>>>>> static unsigned int list_count; >>>>>>> +static struct resource *target_resource; >>>>>>> +static struct resource xen_resource = { >>>>>>> + .name = "Xen unused space", >>>>>>> +}; >>>>>>> + >>>>>>> +/* >>>>>>> + * If arch is not happy with system "iomem_resource" being used for >>>>>>> + * the region allocation it can provide it's own view by >>>>>>> initializing >>>>>>> + * "xen_resource" with unused regions of guest physical address >>>>>>> space >>>>>>> + * provided by the hypervisor. >>>>>>> + */ >>>>>>> +int __weak arch_xen_unpopulated_init(struct resource *res) >>>>>>> +{ >>>>>>> + return -ENOSYS; >>>>>>> +} >>>>>>> + >>>>>>> static int fill_list(unsigned int nr_pages) >>>>>>> { >>>>>>> struct dev_pagemap *pgmap; >>>>>>> - struct resource *res; >>>>>>> + struct resource *res, *tmp_res = NULL; >>>>>>> void *vaddr; >>>>>>> unsigned int i, alloc_pages = round_up(nr_pages, >>>>>>> PAGES_PER_SECTION); >>>>>>> - int ret = -ENOMEM; >>>>>>> + int ret; >>>>>>> res = kzalloc(sizeof(*res), GFP_KERNEL); >>>>>>> if (!res) >>>>>>> @@ -30,7 +47,7 @@ static int fill_list(unsigned int nr_pages) >>>>>>> res->name = "Xen scratch"; >>>>>>> res->flags = IORESOURCE_MEM | IORESOURCE_BUSY; >>>>>>> - ret = allocate_resource(&iomem_resource, res, >>>>>>> + ret = allocate_resource(target_resource, res, >>>>>>> alloc_pages * PAGE_SIZE, 0, -1, >>>>>>> PAGES_PER_SECTION * PAGE_SIZE, NULL, >>>>>>> NULL); >>>>>>> if (ret < 0) { >>>>>>> @@ -38,6 +55,31 @@ static int fill_list(unsigned int nr_pages) >>>>>>> goto err_resource; >>>>>>> } >>>>>>> + /* >>>>>>> + * Reserve the region previously allocated from Xen resource >>>>>>> to avoid >>>>>>> + * re-using it by someone else. >>>>>>> + */ >>>>>>> + if (target_resource != &iomem_resource) { >>>>>>> + tmp_res = kzalloc(sizeof(*tmp_res), GFP_KERNEL); >>>>>>> + if (!res) { >>>>>>> + ret = -ENOMEM; >>>>>>> + goto err_insert; >>>>>>> + } >>>>>>> + >>>>>>> + tmp_res->name = res->name; >>>>>>> + tmp_res->start = res->start; >>>>>>> + tmp_res->end = res->end; >>>>>>> + tmp_res->flags = res->flags; >>>>>>> + >>>>>>> + ret = insert_resource(&iomem_resource, tmp_res); >>>>>>> + if (ret < 0) { >>>>>>> + pr_err("Cannot insert IOMEM resource [%llx - >>>>>>> %llx]\n", >>>>>>> + tmp_res->start, tmp_res->end); >>>>>>> + kfree(tmp_res); >>>>>>> + goto err_insert; >>>>>>> + } >>>>>>> + } >>>>>> I am a bit confused.. why do we need to do this? Who could be >>>>>> erroneously re-using the region? Are you saying that the next time >>>>>> allocate_resource is called it could find the same region again? It >>>>>> doesn't seem possible? >>>>> No, as I understand the allocate_resource() being called for the >>>>> same root >>>>> resource won't provide the same region... We only need to do this >>>>> (insert >>>>> the >>>>> region into "iomem_resource") if we allocated it from our *internal* >>>>> "xen_resource", as *global* "iomem_resource" (which is used >>>>> everywhere) is >>>>> not >>>>> aware of that region has been already allocated. So inserting a region >>>>> here we >>>>> reserving it, otherwise it could be reused elsewhere. >>>> But elsewhere where? >>> I think, theoretically everywhere where >>> allocate_resource(&iomem_resource, >>> ...) is called. >>> >>> >>>> Let's say that allocate_resource allocates a range from xen_resource. >>>> From reading the code, it doesn't look like iomem_resource would have >>>> that range because the extended regions described under /hypervisor are >>>> not added automatically to iomem_resource. >>>> >>>> So what if we don't call insert_resource? Nothing could allocate the >>>> same range because iomem_resource doesn't have it at all and >>>> xen_resource is not used anywhere if not here. >>>> >>>> What am I missing? >>> >>> Below my understanding which, of course, might be wrong. >>> >>> If we don't claim resource by calling insert_resource (or even >>> request_resource) here then the same range could be allocated >>> everywhere where >>> allocate_resource(&iomem_resource, ...) is called. >>> I don't see what prevents the same range from being allocated. Why >>> actually >>> allocate_resource(&iomem_resource, ...) can't provide the same range >>> if it is >>> free (not-reserved-yet) from it's PoV? The comment above >>> allocate_resource() >>> says "allocate empty slot in the resource tree given range & >>> alignment". So >>> this "empty slot" could be exactly the same range. >>> >>> I experimented with that a bit trying to call >>> allocate_resource(&iomem_resource, ...) several times in another >>> place to see >>> what ranges it returns in both cases (w/ and w/o calling insert_resource >>> here). So an experiment confirmed (of course, if I made it correctly) >>> that the >>> same range could be allocated if we didn't call insert_resource() >>> here. And as >>> I understand there is nothing strange here, as iomem_resource covers all >>> address space initially (0, -1) and everything *not* >>> inserted/requested (in >>> other words, reserved) yet is considered as free and could be >>> provided if fits >>> constraints. Or I really missed something? >> Thanks for the explanation! It was me that didn't know that >> iomem_resource covers all the address space initially. I thought it was >> populated only with actual iomem ranges. Now it makes sense, thanks! >> >> >>> It feels to me that it would be better to call request_resource() >>> instead of >>> insert_resource(). It seems, that if no conflict happens both >>> functions will >>> behave in same way, but in case of conflict if the conflicting resource >>> entirely fit the new resource the former will return an error. I >>> think, this >>> way we will be able to detect that a range we are trying to reserve >>> is already >>> present and bail out early. >>> >>> >>>> Or maybe it is the other way around: core Linux code assumes everything >>>> is described in iomem_resource so something under kernel/ or mm/ would >>>> crash if we start using a page pointing to an address missing from >>>> iomem_resource? >>>>>>> pgmap = kzalloc(sizeof(*pgmap), GFP_KERNEL); >>>>>>> if (!pgmap) { >>>>>>> ret = -ENOMEM; >>>>>>> @@ -95,12 +137,40 @@ static int fill_list(unsigned int nr_pages) >>>>>>> err_memremap: >>>>>>> kfree(pgmap); >>>>>>> err_pgmap: >>>>>>> + if (tmp_res) { >>>>>>> + release_resource(tmp_res); >>>>>>> + kfree(tmp_res); >>>>>>> + } >>>>>>> +err_insert: >>>>>>> release_resource(res); >>>>>>> err_resource: >>>>>>> kfree(res); >>>>>>> return ret; >>>>>>> } >>>>>>> +static void unpopulated_init(void) >>>>>>> +{ >>>>>>> + static bool inited = false; >>>>>> initialized = false >>>>> ok. >>>>> >>>>> >>>>>>> + int ret; >>>>>>> + >>>>>>> + if (inited) >>>>>>> + return; >>>>>>> + >>>>>>> + /* >>>>>>> + * Try to initialize Xen resource the first and fall back to >>>>>>> default >>>>>>> + * resource if arch doesn't offer one. >>>>>>> + */ >>>>>>> + ret = arch_xen_unpopulated_init(&xen_resource); >>>>>>> + if (!ret) >>>>>>> + target_resource = &xen_resource; >>>>>>> + else if (ret == -ENOSYS) >>>>>>> + target_resource = &iomem_resource; >>>>>>> + else >>>>>>> + pr_err("Cannot initialize Xen resource\n"); >>>>>>> + >>>>>>> + inited = true; >>>>>>> +} >>>>>> Would it make sense to call unpopulated_init from an init function, >>>>>> rather than every time xen_alloc_unpopulated_pages is called? >>>>> Good point, thank you. Will do. To be honest, I also don't like the >>>>> current >>>>> approach much. >>>>> >>>>> >>>>>>> /** >>>>>>> * xen_alloc_unpopulated_pages - alloc unpopulated pages >>>>>>> * @nr_pages: Number of pages >>>>>>> @@ -112,6 +182,16 @@ int xen_alloc_unpopulated_pages(unsigned int >>>>>>> nr_pages, struct page **pages) >>>>>>> unsigned int i; >>>>>>> int ret = 0; >>>>>>> + unpopulated_init(); >>>>>>> + >>>>>>> + /* >>>>>>> + * Fall back to default behavior if we do not have any >>>>>>> suitable >>>>>>> resource >>>>>>> + * to allocate required region from and as the result we won't >>>>>>> be able >>>>>>> to >>>>>>> + * construct pages. >>>>>>> + */ >>>>>>> + if (!target_resource) >>>>>>> + return alloc_xenballooned_pages(nr_pages, pages); >>>>>> The commit message says that the behavior on x86 doesn't change >>>>>> but this >>>>>> seems to be a change that could impact x86? >>>>> I don't think, however I didn't tested on x86 and might be wrong, but >>>>> according to the current patch, on x86 the "target_resource" is always >>>>> valid >>>>> and points to the "iomem_resource" as arch_xen_unpopulated_init() >>>>> is not >>>>> implemented. So there won't be any fallback to use >>>>> alloc_(free)_xenballooned_pages() here and fill_list() will behave as >>>>> usual. >>>> If target_resource is always valid, then we don't need this special >>>> check. In fact, the condition should never be true. >>> >>> The target_resource is always valid and points to the >>> "iomem_resource" on x86 >>> (this is equivalent to the behavior before this patch). >>> On Arm target_resource might be NULL if arch_xen_unpopulated_init() >>> failed, >>> for example, if no extended regions reported by the hypervisor. >>> We cannot use "iomem_resource" on Arm, only a resource constructed from >>> extended regions. This is why I added that check (and fallback to >>> xenballooned >>> pages). >>> What I was thinking is that in case of using old Xen (although we >>> would need >>> to balloon out RAM pages) we still would be able to keep working, so >>> no need >>> to disable CONFIG_XEN_UNPOPULATED_ALLOC on such setups. >>>>> You raised a really good question, on Arm we need a fallback to >>>>> balloon >>>>> out >>>>> RAM pages again if hypervisor doesn't provide extended regions (we >>>>> run on >>>>> old >>>>> version, no unused regions with reasonable size, etc), so I decided >>>>> to put >>>>> a >>>>> fallback code here, an indicator of the failure is invalid >>>>> "target_resource". >>>> I think it is unnecessary as we already assume today that >>>> &iomem_resource is always available. >>>>> I noticed the patch which is about to be upstreamed that removes >>>>> alloc_(free)xenballooned_pages API [1]. Right now I have no idea >>>>> how/where >>>>> this fallback could be implemented as this is under build option >>>>> control >>>>> (CONFIG_XEN_UNPOPULATED_ALLOC). So the API with the same name is >>>>> either >>>>> used >>>>> for unpopulated pages (if set) or ballooned pages (if not set). I >>>>> would >>>>> appreciate suggestions regarding that. I am wondering would it be >>>>> possible >>>>> and >>>>> correctly to have both mechanisms (unpopulated and ballooned) >>>>> enabled by >>>>> default and some init code to decide which one to use at runtime or >>>>> some >>>>> sort? >>>> I would keep it simple and remove the fallback from this patch. So: >>>> >>>> - if not CONFIG_XEN_UNPOPULATED_ALLOC, then balloon >>>> - if CONFIG_XEN_UNPOPULATED_ALLOC, then >>>> - xen_resource if present >>>> - otherwise iomem_resource >>> Unfortunately, we cannot use iomem_resource on Arm safely, either >>> xen_resource >>> or fail (if no fallback exists). >>> >>> >>>> The xen_resource/iomem_resource config can be done at init time using >>>> target_resource. At runtime, target_resource is always != NULL so we >>>> just go ahead and use it. >>> >>> Thank you for the suggestion. OK, let's keep it simple and drop fallback >>> attempts for now. With one remark: >>> We will make CONFIG_XEN_UNPOPULATED_ALLOC disabled by default on Arm >>> in next >>> patch. So by default everything will behave as usual on Arm (balloon >>> out RAM >>> pages), >>> if user knows for sure that Xen reports extended regions, he/she can >>> enable >>> the config. This way we won't break anything. What do you think? >> Actually after reading your replies and explanation I changed opinion: I >> think we do need the fallback because Linux cannot really assume that >> it is running on "new Xen" so it definitely needs to keep working if >> CONFIG_XEN_UNPOPULATED_ALLOC is enabled and the extended regions are not >> advertised. >> >> I think we'll have to roll back some of the changes introduced by >> 121f2faca2c0a. That's because even if CONFIG_XEN_UNPOPULATED_ALLOC is >> enabled we cannot know if we can use unpopulated-alloc or whether we >> have to use alloc_xenballooned_pages until we parse the /hypervisor node >> in device tree at runtime. > > Exactly! > > >> >> In short, we cannot switch between unpopulated-alloc and >> alloc_xenballooned_pages at build time, we have to do it at runtime >> (boot time). > > +1 > > > I created a patch to partially revert 121f2faca2c0a "xen/balloon: rename > alloc/free_xenballooned_pages". > > If there is no objections I will add it to V3 (which is almost ready, > except the fallback bits). Could you please tell me what do you think? > > > From dc79bcd425358596d95e715a8bd8b81deaaeb703 Mon Sep 17 00:00:00 2001 > From: Oleksandr Tyshchenko <oleksandr_tyshchenko@epam.com> > Date: Tue, 23 Nov 2021 18:14:41 +0200 > Subject: [PATCH] xen/balloon: Bring alloc(free)_xenballooned_pages helpers > back > > This patch rolls back some of the changes introduced by commit > 121f2faca2c0a "xen/balloon: rename alloc/free_xenballooned_pages" > in order to make possible to still allocate xenballooned pages > if CONFIG_XEN_UNPOPULATED_ALLOC is enabled. > > On Arm the unpopulated pages will be allocated on top of extended > regions provided by Xen via device-tree (the subsequent patches > will add required bits to support unpopulated-alloc feature on Arm). > The problem is that extended regions feature has been introduced > into Xen quite recently (during 4.16 release cycle). So this > effectively means that Linux must only use unpopulated-alloc on Arm > if it is running on "new Xen" which advertises these regions. > But, it will only be known after parsing the "hypervisor" node > at boot time, so before doing that we cannot assume anything. > > In order to keep working if CONFIG_XEN_UNPOPULATED_ALLOC is enabled > and the extended regions are not advertised (Linux is running on > "old Xen", etc) we need the fallback to alloc_xenballooned_pages(). > > This way we wouldn't reduce the amount of memory usable (wasting > RAM pages) for any of the external mappings anymore (and eliminate > XSA-300) with "new Xen", but would be still functional ballooning > out RAM pages with "old Xen". > > Also rename alloc(free)_xenballooned_pages to > xen_alloc(free)_ballooned_pages. > > Signed-off-by: Oleksandr Tyshchenko <oleksandr_tyshchenko@epam.com> > --- > drivers/xen/balloon.c | 20 +++++++++----------- > include/xen/balloon.h | 3 +++ > include/xen/xen.h | 6 ++++++ > 3 files changed, 18 insertions(+), 11 deletions(-) > > diff --git a/drivers/xen/balloon.c b/drivers/xen/balloon.c > index ba2ea11..a2c4fc49 100644 > --- a/drivers/xen/balloon.c > +++ b/drivers/xen/balloon.c > @@ -581,7 +581,6 @@ void balloon_set_new_target(unsigned long target) > } > EXPORT_SYMBOL_GPL(balloon_set_new_target); > > -#ifndef CONFIG_XEN_UNPOPULATED_ALLOC > static int add_ballooned_pages(unsigned int nr_pages) > { > enum bp_state st; > @@ -610,12 +609,12 @@ static int add_ballooned_pages(unsigned int nr_pages) > } > > /** > - * xen_alloc_unpopulated_pages - get pages that have been ballooned out > + * xen_alloc_ballooned_pages - get pages that have been ballooned out > * @nr_pages: Number of pages to get > * @pages: pages returned > * @return 0 on success, error otherwise > */ > -int xen_alloc_unpopulated_pages(unsigned int nr_pages, struct page > **pages) > +int xen_alloc_ballooned_pages(unsigned int nr_pages, struct page **pages) > { > unsigned int pgno = 0; > struct page *page; > @@ -652,23 +651,23 @@ int xen_alloc_unpopulated_pages(unsigned int > nr_pages, struct page **pages) > return 0; > out_undo: > mutex_unlock(&balloon_mutex); > - xen_free_unpopulated_pages(pgno, pages); > + xen_free_ballooned_pages(pgno, pages); > /* > - * NB: free_xenballooned_pages will only subtract pgno pages, but > since > + * NB: xen_free_ballooned_pages will only subtract pgno pages, but > since > * target_unpopulated is incremented with nr_pages at the start we > need > * to remove the remaining ones also, or accounting will be screwed. > */ > balloon_stats.target_unpopulated -= nr_pages - pgno; > return ret; > } > -EXPORT_SYMBOL(xen_alloc_unpopulated_pages); > +EXPORT_SYMBOL(xen_alloc_ballooned_pages); > > /** > - * xen_free_unpopulated_pages - return pages retrieved with > get_ballooned_pages > + * xen_free_ballooned_pages - return pages retrieved with > get_ballooned_pages > * @nr_pages: Number of pages > * @pages: pages to return > */ > -void xen_free_unpopulated_pages(unsigned int nr_pages, struct page > **pages) > +void xen_free_ballooned_pages(unsigned int nr_pages, struct page **pages) > { > unsigned int i; > > @@ -687,9 +686,9 @@ void xen_free_unpopulated_pages(unsigned int > nr_pages, struct page **pages) > > mutex_unlock(&balloon_mutex); > } > -EXPORT_SYMBOL(xen_free_unpopulated_pages); > +EXPORT_SYMBOL(xen_free_ballooned_pages); > > -#if defined(CONFIG_XEN_PV) > +#if defined(CONFIG_XEN_PV) && !defined(CONFIG_XEN_UNPOPULATED_ALLOC) > static void __init balloon_add_region(unsigned long start_pfn, > unsigned long pages) > { > @@ -712,7 +711,6 @@ static void __init balloon_add_region(unsigned long > start_pfn, > balloon_stats.total_pages += extra_pfn_end - start_pfn; > } > #endif > -#endif > > static int __init balloon_init(void) > { > diff --git a/include/xen/balloon.h b/include/xen/balloon.h > index e93d4f0..f78a6cc 100644 > --- a/include/xen/balloon.h > +++ b/include/xen/balloon.h > @@ -26,6 +26,9 @@ extern struct balloon_stats balloon_stats; > > void balloon_set_new_target(unsigned long target); > > +int xen_alloc_ballooned_pages(unsigned int nr_pages, struct page **pages); > +void xen_free_ballooned_pages(unsigned int nr_pages, struct page **pages); > + > #ifdef CONFIG_XEN_BALLOON > void xen_balloon_init(void); > #else > diff --git a/include/xen/xen.h b/include/xen/xen.h > index 9f031b5..410e3e4 100644 > --- a/include/xen/xen.h > +++ b/include/xen/xen.h > @@ -52,7 +52,13 @@ bool xen_biovec_phys_mergeable(const struct bio_vec > *vec1, > extern u64 xen_saved_max_mem_size; > #endif > > +#ifdef CONFIG_XEN_UNPOPULATED_ALLOC > int xen_alloc_unpopulated_pages(unsigned int nr_pages, struct page > **pages); > void xen_free_unpopulated_pages(unsigned int nr_pages, struct page > **pages); > +#else > +#define xen_alloc_unpopulated_pages xen_alloc_ballooned_pages > +#define xen_free_unpopulated_pages xen_free_ballooned_pages Could you please make those inline functions instead? Other than that I'm fine with the approach. Juergen
On 23.11.21 23:25, Stefano Stabellini wrote: Hi Stefano > On Tue, 23 Nov 2021, Oleksandr wrote: >>> Actually after reading your replies and explanation I changed opinion: I >>> think we do need the fallback because Linux cannot really assume that >>> it is running on "new Xen" so it definitely needs to keep working if >>> CONFIG_XEN_UNPOPULATED_ALLOC is enabled and the extended regions are not >>> advertised. >>> >>> I think we'll have to roll back some of the changes introduced by >>> 121f2faca2c0a. That's because even if CONFIG_XEN_UNPOPULATED_ALLOC is >>> enabled we cannot know if we can use unpopulated-alloc or whether we >>> have to use alloc_xenballooned_pages until we parse the /hypervisor node >>> in device tree at runtime. >> Exactly! >> >> >>> In short, we cannot switch between unpopulated-alloc and >>> alloc_xenballooned_pages at build time, we have to do it at runtime >>> (boot time). >> +1 >> >> >> I created a patch to partially revert 121f2faca2c0a "xen/balloon: rename >> alloc/free_xenballooned_pages". >> >> If there is no objections I will add it to V3 (which is almost ready, except >> the fallback bits). Could you please tell me what do you think? > > It makes sense to me. You can add my Reviewed-by. Great, thank you! > > >> From dc79bcd425358596d95e715a8bd8b81deaaeb703 Mon Sep 17 00:00:00 2001 >> From: Oleksandr Tyshchenko <oleksandr_tyshchenko@epam.com> >> Date: Tue, 23 Nov 2021 18:14:41 +0200 >> Subject: [PATCH] xen/balloon: Bring alloc(free)_xenballooned_pages helpers >> back >> >> This patch rolls back some of the changes introduced by commit >> 121f2faca2c0a "xen/balloon: rename alloc/free_xenballooned_pages" >> in order to make possible to still allocate xenballooned pages >> if CONFIG_XEN_UNPOPULATED_ALLOC is enabled. >> >> On Arm the unpopulated pages will be allocated on top of extended >> regions provided by Xen via device-tree (the subsequent patches >> will add required bits to support unpopulated-alloc feature on Arm). >> The problem is that extended regions feature has been introduced >> into Xen quite recently (during 4.16 release cycle). So this >> effectively means that Linux must only use unpopulated-alloc on Arm >> if it is running on "new Xen" which advertises these regions. >> But, it will only be known after parsing the "hypervisor" node >> at boot time, so before doing that we cannot assume anything. >> >> In order to keep working if CONFIG_XEN_UNPOPULATED_ALLOC is enabled >> and the extended regions are not advertised (Linux is running on >> "old Xen", etc) we need the fallback to alloc_xenballooned_pages(). >> >> This way we wouldn't reduce the amount of memory usable (wasting >> RAM pages) for any of the external mappings anymore (and eliminate >> XSA-300) with "new Xen", but would be still functional ballooning >> out RAM pages with "old Xen". >> >> Also rename alloc(free)_xenballooned_pages to xen_alloc(free)_ballooned_pages. >> >> Signed-off-by: Oleksandr Tyshchenko <oleksandr_tyshchenko@epam.com> >> --- >> drivers/xen/balloon.c | 20 +++++++++----------- >> include/xen/balloon.h | 3 +++ >> include/xen/xen.h | 6 ++++++ >> 3 files changed, 18 insertions(+), 11 deletions(-) >> >> diff --git a/drivers/xen/balloon.c b/drivers/xen/balloon.c >> index ba2ea11..a2c4fc49 100644 >> --- a/drivers/xen/balloon.c >> +++ b/drivers/xen/balloon.c >> @@ -581,7 +581,6 @@ void balloon_set_new_target(unsigned long target) >> } >> EXPORT_SYMBOL_GPL(balloon_set_new_target); >> >> -#ifndef CONFIG_XEN_UNPOPULATED_ALLOC >> static int add_ballooned_pages(unsigned int nr_pages) >> { >> enum bp_state st; >> @@ -610,12 +609,12 @@ static int add_ballooned_pages(unsigned int nr_pages) >> } >> >> /** >> - * xen_alloc_unpopulated_pages - get pages that have been ballooned out >> + * xen_alloc_ballooned_pages - get pages that have been ballooned out >> * @nr_pages: Number of pages to get >> * @pages: pages returned >> * @return 0 on success, error otherwise >> */ >> -int xen_alloc_unpopulated_pages(unsigned int nr_pages, struct page **pages) >> +int xen_alloc_ballooned_pages(unsigned int nr_pages, struct page **pages) >> { >> unsigned int pgno = 0; >> struct page *page; >> @@ -652,23 +651,23 @@ int xen_alloc_unpopulated_pages(unsigned int nr_pages, >> struct page **pages) >> return 0; >> out_undo: >> mutex_unlock(&balloon_mutex); >> - xen_free_unpopulated_pages(pgno, pages); >> + xen_free_ballooned_pages(pgno, pages); >> /* >> - * NB: free_xenballooned_pages will only subtract pgno pages, but since >> + * NB: xen_free_ballooned_pages will only subtract pgno pages, but since >> * target_unpopulated is incremented with nr_pages at the start we need >> * to remove the remaining ones also, or accounting will be screwed. >> */ >> balloon_stats.target_unpopulated -= nr_pages - pgno; >> return ret; >> } >> -EXPORT_SYMBOL(xen_alloc_unpopulated_pages); >> +EXPORT_SYMBOL(xen_alloc_ballooned_pages); >> >> /** >> - * xen_free_unpopulated_pages - return pages retrieved with >> get_ballooned_pages >> + * xen_free_ballooned_pages - return pages retrieved with get_ballooned_pages >> * @nr_pages: Number of pages >> * @pages: pages to return >> */ >> -void xen_free_unpopulated_pages(unsigned int nr_pages, struct page **pages) >> +void xen_free_ballooned_pages(unsigned int nr_pages, struct page **pages) >> { >> unsigned int i; >> >> @@ -687,9 +686,9 @@ void xen_free_unpopulated_pages(unsigned int nr_pages, >> struct page **pages) >> >> mutex_unlock(&balloon_mutex); >> } >> -EXPORT_SYMBOL(xen_free_unpopulated_pages); >> +EXPORT_SYMBOL(xen_free_ballooned_pages); >> >> -#if defined(CONFIG_XEN_PV) >> +#if defined(CONFIG_XEN_PV) && !defined(CONFIG_XEN_UNPOPULATED_ALLOC) >> static void __init balloon_add_region(unsigned long start_pfn, >> unsigned long pages) >> { >> @@ -712,7 +711,6 @@ static void __init balloon_add_region(unsigned long >> start_pfn, >> balloon_stats.total_pages += extra_pfn_end - start_pfn; >> } >> #endif >> -#endif >> >> static int __init balloon_init(void) >> { >> diff --git a/include/xen/balloon.h b/include/xen/balloon.h >> index e93d4f0..f78a6cc 100644 >> --- a/include/xen/balloon.h >> +++ b/include/xen/balloon.h >> @@ -26,6 +26,9 @@ extern struct balloon_stats balloon_stats; >> >> void balloon_set_new_target(unsigned long target); >> >> +int xen_alloc_ballooned_pages(unsigned int nr_pages, struct page **pages); >> +void xen_free_ballooned_pages(unsigned int nr_pages, struct page **pages); >> + >> #ifdef CONFIG_XEN_BALLOON >> void xen_balloon_init(void); >> #else >> diff --git a/include/xen/xen.h b/include/xen/xen.h >> index 9f031b5..410e3e4 100644 >> --- a/include/xen/xen.h >> +++ b/include/xen/xen.h >> @@ -52,7 +52,13 @@ bool xen_biovec_phys_mergeable(const struct bio_vec *vec1, >> extern u64 xen_saved_max_mem_size; >> #endif >> >> +#ifdef CONFIG_XEN_UNPOPULATED_ALLOC >> int xen_alloc_unpopulated_pages(unsigned int nr_pages, struct page **pages); >> void xen_free_unpopulated_pages(unsigned int nr_pages, struct page **pages); >> +#else >> +#define xen_alloc_unpopulated_pages xen_alloc_ballooned_pages >> +#define xen_free_unpopulated_pages xen_free_ballooned_pages >> +#include <xen/balloon.h> >> +#endif >> >> #endif /* _XEN_XEN_H */
On 24.11.21 07:16, Juergen Gross wrote: Hi Juergen > On 23.11.21 17:46, Oleksandr wrote: >> >> On 20.11.21 04:19, Stefano Stabellini wrote: >> >> Hi Stefano, Juergen, all >> >> >>> Juergen please see the bottom of the email >>> >>> On Fri, 19 Nov 2021, Oleksandr wrote: >>>> On 19.11.21 02:59, Stefano Stabellini wrote: >>>>> On Tue, 9 Nov 2021, Oleksandr wrote: >>>>>> On 28.10.21 19:37, Stefano Stabellini wrote: >>>>>> >>>>>> Hi Stefano >>>>>> >>>>>> I am sorry for the late response. >>>>>> >>>>>>> On Tue, 26 Oct 2021, Oleksandr Tyshchenko wrote: >>>>>>>> From: Oleksandr Tyshchenko <oleksandr_tyshchenko@epam.com> >>>>>>>> >>>>>>>> The main reason of this change is that unpopulated-alloc >>>>>>>> code cannot be used in its current form on Arm, but there >>>>>>>> is a desire to reuse it to avoid wasting real RAM pages >>>>>>>> for the grant/foreign mappings. >>>>>>>> >>>>>>>> The problem is that system "iomem_resource" is used for >>>>>>>> the address space allocation, but the really unallocated >>>>>>>> space can't be figured out precisely by the domain on Arm >>>>>>>> without hypervisor involvement. For example, not all device >>>>>>>> I/O regions are known by the time domain starts creating >>>>>>>> grant/foreign mappings. And following the advise from >>>>>>>> "iomem_resource" we might end up reusing these regions by >>>>>>>> a mistake. So, the hypervisor which maintains the P2M for >>>>>>>> the domain is in the best position to provide unused regions >>>>>>>> of guest physical address space which could be safely used >>>>>>>> to create grant/foreign mappings. >>>>>>>> >>>>>>>> Introduce new helper arch_xen_unpopulated_init() which purpose >>>>>>>> is to create specific Xen resource based on the memory regions >>>>>>>> provided by the hypervisor to be used as unused space for Xen >>>>>>>> scratch pages. >>>>>>>> >>>>>>>> If arch doesn't implement arch_xen_unpopulated_init() to >>>>>>>> initialize Xen resource the default "iomem_resource" will be used. >>>>>>>> So the behavior on x86 won't be changed. >>>>>>>> >>>>>>>> Also fall back to allocate xenballooned pages (steal real RAM >>>>>>>> pages) if we do not have any suitable resource to work with and >>>>>>>> as the result we won't be able to provide unpopulated pages. >>>>>>>> >>>>>>>> Signed-off-by: Oleksandr Tyshchenko >>>>>>>> <oleksandr_tyshchenko@epam.com> >>>>>>>> --- >>>>>>>> Changes RFC -> V2: >>>>>>>> - new patch, instead of >>>>>>>> "[RFC PATCH 2/2] xen/unpopulated-alloc: Query hypervisor to >>>>>>>> provide >>>>>>>> unallocated space" >>>>>>>> --- >>>>>>>> drivers/xen/unpopulated-alloc.c | 89 >>>>>>>> +++++++++++++++++++++++++++++++++++++++-- >>>>>>>> include/xen/xen.h | 2 + >>>>>>>> 2 files changed, 88 insertions(+), 3 deletions(-) >>>>>>>> >>>>>>>> diff --git a/drivers/xen/unpopulated-alloc.c >>>>>>>> b/drivers/xen/unpopulated-alloc.c >>>>>>>> index a03dc5b..1f1d8d8 100644 >>>>>>>> --- a/drivers/xen/unpopulated-alloc.c >>>>>>>> +++ b/drivers/xen/unpopulated-alloc.c >>>>>>>> @@ -8,6 +8,7 @@ >>>>>>>> #include <asm/page.h> >>>>>>>> +#include <xen/balloon.h> >>>>>>>> #include <xen/page.h> >>>>>>>> #include <xen/xen.h> >>>>>>>> @@ -15,13 +16,29 @@ static DEFINE_MUTEX(list_lock); >>>>>>>> static struct page *page_list; >>>>>>>> static unsigned int list_count; >>>>>>>> +static struct resource *target_resource; >>>>>>>> +static struct resource xen_resource = { >>>>>>>> + .name = "Xen unused space", >>>>>>>> +}; >>>>>>>> + >>>>>>>> +/* >>>>>>>> + * If arch is not happy with system "iomem_resource" being >>>>>>>> used for >>>>>>>> + * the region allocation it can provide it's own view by >>>>>>>> initializing >>>>>>>> + * "xen_resource" with unused regions of guest physical >>>>>>>> address space >>>>>>>> + * provided by the hypervisor. >>>>>>>> + */ >>>>>>>> +int __weak arch_xen_unpopulated_init(struct resource *res) >>>>>>>> +{ >>>>>>>> + return -ENOSYS; >>>>>>>> +} >>>>>>>> + >>>>>>>> static int fill_list(unsigned int nr_pages) >>>>>>>> { >>>>>>>> struct dev_pagemap *pgmap; >>>>>>>> - struct resource *res; >>>>>>>> + struct resource *res, *tmp_res = NULL; >>>>>>>> void *vaddr; >>>>>>>> unsigned int i, alloc_pages = round_up(nr_pages, >>>>>>>> PAGES_PER_SECTION); >>>>>>>> - int ret = -ENOMEM; >>>>>>>> + int ret; >>>>>>>> res = kzalloc(sizeof(*res), GFP_KERNEL); >>>>>>>> if (!res) >>>>>>>> @@ -30,7 +47,7 @@ static int fill_list(unsigned int nr_pages) >>>>>>>> res->name = "Xen scratch"; >>>>>>>> res->flags = IORESOURCE_MEM | IORESOURCE_BUSY; >>>>>>>> - ret = allocate_resource(&iomem_resource, res, >>>>>>>> + ret = allocate_resource(target_resource, res, >>>>>>>> alloc_pages * PAGE_SIZE, 0, -1, >>>>>>>> PAGES_PER_SECTION * PAGE_SIZE, NULL, >>>>>>>> NULL); >>>>>>>> if (ret < 0) { >>>>>>>> @@ -38,6 +55,31 @@ static int fill_list(unsigned int nr_pages) >>>>>>>> goto err_resource; >>>>>>>> } >>>>>>>> + /* >>>>>>>> + * Reserve the region previously allocated from Xen resource >>>>>>>> to avoid >>>>>>>> + * re-using it by someone else. >>>>>>>> + */ >>>>>>>> + if (target_resource != &iomem_resource) { >>>>>>>> + tmp_res = kzalloc(sizeof(*tmp_res), GFP_KERNEL); >>>>>>>> + if (!res) { >>>>>>>> + ret = -ENOMEM; >>>>>>>> + goto err_insert; >>>>>>>> + } >>>>>>>> + >>>>>>>> + tmp_res->name = res->name; >>>>>>>> + tmp_res->start = res->start; >>>>>>>> + tmp_res->end = res->end; >>>>>>>> + tmp_res->flags = res->flags; >>>>>>>> + >>>>>>>> + ret = insert_resource(&iomem_resource, tmp_res); >>>>>>>> + if (ret < 0) { >>>>>>>> + pr_err("Cannot insert IOMEM resource [%llx - >>>>>>>> %llx]\n", >>>>>>>> + tmp_res->start, tmp_res->end); >>>>>>>> + kfree(tmp_res); >>>>>>>> + goto err_insert; >>>>>>>> + } >>>>>>>> + } >>>>>>> I am a bit confused.. why do we need to do this? Who could be >>>>>>> erroneously re-using the region? Are you saying that the next time >>>>>>> allocate_resource is called it could find the same region again? It >>>>>>> doesn't seem possible? >>>>>> No, as I understand the allocate_resource() being called for the >>>>>> same root >>>>>> resource won't provide the same region... We only need to do this >>>>>> (insert >>>>>> the >>>>>> region into "iomem_resource") if we allocated it from our *internal* >>>>>> "xen_resource", as *global* "iomem_resource" (which is used >>>>>> everywhere) is >>>>>> not >>>>>> aware of that region has been already allocated. So inserting a >>>>>> region >>>>>> here we >>>>>> reserving it, otherwise it could be reused elsewhere. >>>>> But elsewhere where? >>>> I think, theoretically everywhere where >>>> allocate_resource(&iomem_resource, >>>> ...) is called. >>>> >>>> >>>>> Let's say that allocate_resource allocates a range from xen_resource. >>>>> From reading the code, it doesn't look like iomem_resource would >>>>> have >>>>> that range because the extended regions described under >>>>> /hypervisor are >>>>> not added automatically to iomem_resource. >>>>> >>>>> So what if we don't call insert_resource? Nothing could allocate the >>>>> same range because iomem_resource doesn't have it at all and >>>>> xen_resource is not used anywhere if not here. >>>>> >>>>> What am I missing? >>>> >>>> Below my understanding which, of course, might be wrong. >>>> >>>> If we don't claim resource by calling insert_resource (or even >>>> request_resource) here then the same range could be allocated >>>> everywhere where >>>> allocate_resource(&iomem_resource, ...) is called. >>>> I don't see what prevents the same range from being allocated. Why >>>> actually >>>> allocate_resource(&iomem_resource, ...) can't provide the same >>>> range if it is >>>> free (not-reserved-yet) from it's PoV? The comment above >>>> allocate_resource() >>>> says "allocate empty slot in the resource tree given range & >>>> alignment". So >>>> this "empty slot" could be exactly the same range. >>>> >>>> I experimented with that a bit trying to call >>>> allocate_resource(&iomem_resource, ...) several times in another >>>> place to see >>>> what ranges it returns in both cases (w/ and w/o calling >>>> insert_resource >>>> here). So an experiment confirmed (of course, if I made it >>>> correctly) that the >>>> same range could be allocated if we didn't call insert_resource() >>>> here. And as >>>> I understand there is nothing strange here, as iomem_resource >>>> covers all >>>> address space initially (0, -1) and everything *not* >>>> inserted/requested (in >>>> other words, reserved) yet is considered as free and could be >>>> provided if fits >>>> constraints. Or I really missed something? >>> Thanks for the explanation! It was me that didn't know that >>> iomem_resource covers all the address space initially. I thought it was >>> populated only with actual iomem ranges. Now it makes sense, thanks! >>> >>> >>>> It feels to me that it would be better to call request_resource() >>>> instead of >>>> insert_resource(). It seems, that if no conflict happens both >>>> functions will >>>> behave in same way, but in case of conflict if the conflicting >>>> resource >>>> entirely fit the new resource the former will return an error. I >>>> think, this >>>> way we will be able to detect that a range we are trying to reserve >>>> is already >>>> present and bail out early. >>>> >>>> >>>>> Or maybe it is the other way around: core Linux code assumes >>>>> everything >>>>> is described in iomem_resource so something under kernel/ or mm/ >>>>> would >>>>> crash if we start using a page pointing to an address missing from >>>>> iomem_resource? >>>>>>>> pgmap = kzalloc(sizeof(*pgmap), GFP_KERNEL); >>>>>>>> if (!pgmap) { >>>>>>>> ret = -ENOMEM; >>>>>>>> @@ -95,12 +137,40 @@ static int fill_list(unsigned int nr_pages) >>>>>>>> err_memremap: >>>>>>>> kfree(pgmap); >>>>>>>> err_pgmap: >>>>>>>> + if (tmp_res) { >>>>>>>> + release_resource(tmp_res); >>>>>>>> + kfree(tmp_res); >>>>>>>> + } >>>>>>>> +err_insert: >>>>>>>> release_resource(res); >>>>>>>> err_resource: >>>>>>>> kfree(res); >>>>>>>> return ret; >>>>>>>> } >>>>>>>> +static void unpopulated_init(void) >>>>>>>> +{ >>>>>>>> + static bool inited = false; >>>>>>> initialized = false >>>>>> ok. >>>>>> >>>>>> >>>>>>>> + int ret; >>>>>>>> + >>>>>>>> + if (inited) >>>>>>>> + return; >>>>>>>> + >>>>>>>> + /* >>>>>>>> + * Try to initialize Xen resource the first and fall back to >>>>>>>> default >>>>>>>> + * resource if arch doesn't offer one. >>>>>>>> + */ >>>>>>>> + ret = arch_xen_unpopulated_init(&xen_resource); >>>>>>>> + if (!ret) >>>>>>>> + target_resource = &xen_resource; >>>>>>>> + else if (ret == -ENOSYS) >>>>>>>> + target_resource = &iomem_resource; >>>>>>>> + else >>>>>>>> + pr_err("Cannot initialize Xen resource\n"); >>>>>>>> + >>>>>>>> + inited = true; >>>>>>>> +} >>>>>>> Would it make sense to call unpopulated_init from an init function, >>>>>>> rather than every time xen_alloc_unpopulated_pages is called? >>>>>> Good point, thank you. Will do. To be honest, I also don't like the >>>>>> current >>>>>> approach much. >>>>>> >>>>>> >>>>>>>> /** >>>>>>>> * xen_alloc_unpopulated_pages - alloc unpopulated pages >>>>>>>> * @nr_pages: Number of pages >>>>>>>> @@ -112,6 +182,16 @@ int xen_alloc_unpopulated_pages(unsigned int >>>>>>>> nr_pages, struct page **pages) >>>>>>>> unsigned int i; >>>>>>>> int ret = 0; >>>>>>>> + unpopulated_init(); >>>>>>>> + >>>>>>>> + /* >>>>>>>> + * Fall back to default behavior if we do not have any >>>>>>>> suitable >>>>>>>> resource >>>>>>>> + * to allocate required region from and as the result we >>>>>>>> won't >>>>>>>> be able >>>>>>>> to >>>>>>>> + * construct pages. >>>>>>>> + */ >>>>>>>> + if (!target_resource) >>>>>>>> + return alloc_xenballooned_pages(nr_pages, pages); >>>>>>> The commit message says that the behavior on x86 doesn't change >>>>>>> but this >>>>>>> seems to be a change that could impact x86? >>>>>> I don't think, however I didn't tested on x86 and might be wrong, >>>>>> but >>>>>> according to the current patch, on x86 the "target_resource" is >>>>>> always >>>>>> valid >>>>>> and points to the "iomem_resource" as arch_xen_unpopulated_init() >>>>>> is not >>>>>> implemented. So there won't be any fallback to use >>>>>> alloc_(free)_xenballooned_pages() here and fill_list() will >>>>>> behave as >>>>>> usual. >>>>> If target_resource is always valid, then we don't need this >>>>> special >>>>> check. In fact, the condition should never be true. >>>> >>>> The target_resource is always valid and points to the >>>> "iomem_resource" on x86 >>>> (this is equivalent to the behavior before this patch). >>>> On Arm target_resource might be NULL if arch_xen_unpopulated_init() >>>> failed, >>>> for example, if no extended regions reported by the hypervisor. >>>> We cannot use "iomem_resource" on Arm, only a resource constructed >>>> from >>>> extended regions. This is why I added that check (and fallback to >>>> xenballooned >>>> pages). >>>> What I was thinking is that in case of using old Xen (although we >>>> would need >>>> to balloon out RAM pages) we still would be able to keep working, >>>> so no need >>>> to disable CONFIG_XEN_UNPOPULATED_ALLOC on such setups. >>>>>> You raised a really good question, on Arm we need a fallback to >>>>>> balloon >>>>>> out >>>>>> RAM pages again if hypervisor doesn't provide extended regions >>>>>> (we run on >>>>>> old >>>>>> version, no unused regions with reasonable size, etc), so I >>>>>> decided to put >>>>>> a >>>>>> fallback code here, an indicator of the failure is invalid >>>>>> "target_resource". >>>>> I think it is unnecessary as we already assume today that >>>>> &iomem_resource is always available. >>>>>> I noticed the patch which is about to be upstreamed that removes >>>>>> alloc_(free)xenballooned_pages API [1]. Right now I have no idea >>>>>> how/where >>>>>> this fallback could be implemented as this is under build option >>>>>> control >>>>>> (CONFIG_XEN_UNPOPULATED_ALLOC). So the API with the same name is >>>>>> either >>>>>> used >>>>>> for unpopulated pages (if set) or ballooned pages (if not set). I >>>>>> would >>>>>> appreciate suggestions regarding that. I am wondering would it be >>>>>> possible >>>>>> and >>>>>> correctly to have both mechanisms (unpopulated and ballooned) >>>>>> enabled by >>>>>> default and some init code to decide which one to use at runtime >>>>>> or some >>>>>> sort? >>>>> I would keep it simple and remove the fallback from this patch. So: >>>>> >>>>> - if not CONFIG_XEN_UNPOPULATED_ALLOC, then balloon >>>>> - if CONFIG_XEN_UNPOPULATED_ALLOC, then >>>>> - xen_resource if present >>>>> - otherwise iomem_resource >>>> Unfortunately, we cannot use iomem_resource on Arm safely, either >>>> xen_resource >>>> or fail (if no fallback exists). >>>> >>>> >>>>> The xen_resource/iomem_resource config can be done at init time using >>>>> target_resource. At runtime, target_resource is always != NULL so we >>>>> just go ahead and use it. >>>> >>>> Thank you for the suggestion. OK, let's keep it simple and drop >>>> fallback >>>> attempts for now. With one remark: >>>> We will make CONFIG_XEN_UNPOPULATED_ALLOC disabled by default on >>>> Arm in next >>>> patch. So by default everything will behave as usual on Arm >>>> (balloon out RAM >>>> pages), >>>> if user knows for sure that Xen reports extended regions, he/she >>>> can enable >>>> the config. This way we won't break anything. What do you think? >>> Actually after reading your replies and explanation I changed >>> opinion: I >>> think we do need the fallback because Linux cannot really assume that >>> it is running on "new Xen" so it definitely needs to keep working if >>> CONFIG_XEN_UNPOPULATED_ALLOC is enabled and the extended regions are >>> not >>> advertised. >>> >>> I think we'll have to roll back some of the changes introduced by >>> 121f2faca2c0a. That's because even if CONFIG_XEN_UNPOPULATED_ALLOC is >>> enabled we cannot know if we can use unpopulated-alloc or whether we >>> have to use alloc_xenballooned_pages until we parse the /hypervisor >>> node >>> in device tree at runtime. >> >> Exactly! >> >> >>> >>> In short, we cannot switch between unpopulated-alloc and >>> alloc_xenballooned_pages at build time, we have to do it at runtime >>> (boot time). >> >> +1 >> >> >> I created a patch to partially revert 121f2faca2c0a "xen/balloon: >> rename alloc/free_xenballooned_pages". >> >> If there is no objections I will add it to V3 (which is almost ready, >> except the fallback bits). Could you please tell me what do you think? >> >> >> From dc79bcd425358596d95e715a8bd8b81deaaeb703 Mon Sep 17 00:00:00 2001 >> From: Oleksandr Tyshchenko <oleksandr_tyshchenko@epam.com> >> Date: Tue, 23 Nov 2021 18:14:41 +0200 >> Subject: [PATCH] xen/balloon: Bring alloc(free)_xenballooned_pages >> helpers >> back >> >> This patch rolls back some of the changes introduced by commit >> 121f2faca2c0a "xen/balloon: rename alloc/free_xenballooned_pages" >> in order to make possible to still allocate xenballooned pages >> if CONFIG_XEN_UNPOPULATED_ALLOC is enabled. >> >> On Arm the unpopulated pages will be allocated on top of extended >> regions provided by Xen via device-tree (the subsequent patches >> will add required bits to support unpopulated-alloc feature on Arm). >> The problem is that extended regions feature has been introduced >> into Xen quite recently (during 4.16 release cycle). So this >> effectively means that Linux must only use unpopulated-alloc on Arm >> if it is running on "new Xen" which advertises these regions. >> But, it will only be known after parsing the "hypervisor" node >> at boot time, so before doing that we cannot assume anything. >> >> In order to keep working if CONFIG_XEN_UNPOPULATED_ALLOC is enabled >> and the extended regions are not advertised (Linux is running on >> "old Xen", etc) we need the fallback to alloc_xenballooned_pages(). >> >> This way we wouldn't reduce the amount of memory usable (wasting >> RAM pages) for any of the external mappings anymore (and eliminate >> XSA-300) with "new Xen", but would be still functional ballooning >> out RAM pages with "old Xen". >> >> Also rename alloc(free)_xenballooned_pages to >> xen_alloc(free)_ballooned_pages. >> >> Signed-off-by: Oleksandr Tyshchenko <oleksandr_tyshchenko@epam.com> >> --- >> drivers/xen/balloon.c | 20 +++++++++----------- >> include/xen/balloon.h | 3 +++ >> include/xen/xen.h | 6 ++++++ >> 3 files changed, 18 insertions(+), 11 deletions(-) >> >> diff --git a/drivers/xen/balloon.c b/drivers/xen/balloon.c >> index ba2ea11..a2c4fc49 100644 >> --- a/drivers/xen/balloon.c >> +++ b/drivers/xen/balloon.c >> @@ -581,7 +581,6 @@ void balloon_set_new_target(unsigned long target) >> } >> EXPORT_SYMBOL_GPL(balloon_set_new_target); >> >> -#ifndef CONFIG_XEN_UNPOPULATED_ALLOC >> static int add_ballooned_pages(unsigned int nr_pages) >> { >> enum bp_state st; >> @@ -610,12 +609,12 @@ static int add_ballooned_pages(unsigned int >> nr_pages) >> } >> >> /** >> - * xen_alloc_unpopulated_pages - get pages that have been ballooned out >> + * xen_alloc_ballooned_pages - get pages that have been ballooned out >> * @nr_pages: Number of pages to get >> * @pages: pages returned >> * @return 0 on success, error otherwise >> */ >> -int xen_alloc_unpopulated_pages(unsigned int nr_pages, struct page >> **pages) >> +int xen_alloc_ballooned_pages(unsigned int nr_pages, struct page >> **pages) >> { >> unsigned int pgno = 0; >> struct page *page; >> @@ -652,23 +651,23 @@ int xen_alloc_unpopulated_pages(unsigned int >> nr_pages, struct page **pages) >> return 0; >> out_undo: >> mutex_unlock(&balloon_mutex); >> - xen_free_unpopulated_pages(pgno, pages); >> + xen_free_ballooned_pages(pgno, pages); >> /* >> - * NB: free_xenballooned_pages will only subtract pgno pages, >> but since >> + * NB: xen_free_ballooned_pages will only subtract pgno pages, >> but since >> * target_unpopulated is incremented with nr_pages at the start >> we need >> * to remove the remaining ones also, or accounting will be >> screwed. >> */ >> balloon_stats.target_unpopulated -= nr_pages - pgno; >> return ret; >> } >> -EXPORT_SYMBOL(xen_alloc_unpopulated_pages); >> +EXPORT_SYMBOL(xen_alloc_ballooned_pages); >> >> /** >> - * xen_free_unpopulated_pages - return pages retrieved with >> get_ballooned_pages >> + * xen_free_ballooned_pages - return pages retrieved with >> get_ballooned_pages >> * @nr_pages: Number of pages >> * @pages: pages to return >> */ >> -void xen_free_unpopulated_pages(unsigned int nr_pages, struct page >> **pages) >> +void xen_free_ballooned_pages(unsigned int nr_pages, struct page >> **pages) >> { >> unsigned int i; >> >> @@ -687,9 +686,9 @@ void xen_free_unpopulated_pages(unsigned int >> nr_pages, struct page **pages) >> >> mutex_unlock(&balloon_mutex); >> } >> -EXPORT_SYMBOL(xen_free_unpopulated_pages); >> +EXPORT_SYMBOL(xen_free_ballooned_pages); >> >> -#if defined(CONFIG_XEN_PV) >> +#if defined(CONFIG_XEN_PV) && !defined(CONFIG_XEN_UNPOPULATED_ALLOC) >> static void __init balloon_add_region(unsigned long start_pfn, >> unsigned long pages) >> { >> @@ -712,7 +711,6 @@ static void __init balloon_add_region(unsigned >> long start_pfn, >> balloon_stats.total_pages += extra_pfn_end - start_pfn; >> } >> #endif >> -#endif >> >> static int __init balloon_init(void) >> { >> diff --git a/include/xen/balloon.h b/include/xen/balloon.h >> index e93d4f0..f78a6cc 100644 >> --- a/include/xen/balloon.h >> +++ b/include/xen/balloon.h >> @@ -26,6 +26,9 @@ extern struct balloon_stats balloon_stats; >> >> void balloon_set_new_target(unsigned long target); >> >> +int xen_alloc_ballooned_pages(unsigned int nr_pages, struct page >> **pages); >> +void xen_free_ballooned_pages(unsigned int nr_pages, struct page >> **pages); >> + >> #ifdef CONFIG_XEN_BALLOON >> void xen_balloon_init(void); >> #else >> diff --git a/include/xen/xen.h b/include/xen/xen.h >> index 9f031b5..410e3e4 100644 >> --- a/include/xen/xen.h >> +++ b/include/xen/xen.h >> @@ -52,7 +52,13 @@ bool xen_biovec_phys_mergeable(const struct >> bio_vec *vec1, >> extern u64 xen_saved_max_mem_size; >> #endif >> >> +#ifdef CONFIG_XEN_UNPOPULATED_ALLOC >> int xen_alloc_unpopulated_pages(unsigned int nr_pages, struct page >> **pages); >> void xen_free_unpopulated_pages(unsigned int nr_pages, struct page >> **pages); >> +#else >> +#define xen_alloc_unpopulated_pages xen_alloc_ballooned_pages >> +#define xen_free_unpopulated_pages xen_free_ballooned_pages > > Could you please make those inline functions instead? Sure, will make. > > > Other than that I'm fine with the approach. Great, thank you! > > > Juergen
diff --git a/drivers/xen/unpopulated-alloc.c b/drivers/xen/unpopulated-alloc.c index a03dc5b..1f1d8d8 100644 --- a/drivers/xen/unpopulated-alloc.c +++ b/drivers/xen/unpopulated-alloc.c @@ -8,6 +8,7 @@ #include <asm/page.h> +#include <xen/balloon.h> #include <xen/page.h> #include <xen/xen.h> @@ -15,13 +16,29 @@ static DEFINE_MUTEX(list_lock); static struct page *page_list; static unsigned int list_count; +static struct resource *target_resource; +static struct resource xen_resource = { + .name = "Xen unused space", +}; + +/* + * If arch is not happy with system "iomem_resource" being used for + * the region allocation it can provide it's own view by initializing + * "xen_resource" with unused regions of guest physical address space + * provided by the hypervisor. + */ +int __weak arch_xen_unpopulated_init(struct resource *res) +{ + return -ENOSYS; +} + static int fill_list(unsigned int nr_pages) { struct dev_pagemap *pgmap; - struct resource *res; + struct resource *res, *tmp_res = NULL; void *vaddr; unsigned int i, alloc_pages = round_up(nr_pages, PAGES_PER_SECTION); - int ret = -ENOMEM; + int ret; res = kzalloc(sizeof(*res), GFP_KERNEL); if (!res) @@ -30,7 +47,7 @@ static int fill_list(unsigned int nr_pages) res->name = "Xen scratch"; res->flags = IORESOURCE_MEM | IORESOURCE_BUSY; - ret = allocate_resource(&iomem_resource, res, + ret = allocate_resource(target_resource, res, alloc_pages * PAGE_SIZE, 0, -1, PAGES_PER_SECTION * PAGE_SIZE, NULL, NULL); if (ret < 0) { @@ -38,6 +55,31 @@ static int fill_list(unsigned int nr_pages) goto err_resource; } + /* + * Reserve the region previously allocated from Xen resource to avoid + * re-using it by someone else. + */ + if (target_resource != &iomem_resource) { + tmp_res = kzalloc(sizeof(*tmp_res), GFP_KERNEL); + if (!res) { + ret = -ENOMEM; + goto err_insert; + } + + tmp_res->name = res->name; + tmp_res->start = res->start; + tmp_res->end = res->end; + tmp_res->flags = res->flags; + + ret = insert_resource(&iomem_resource, tmp_res); + if (ret < 0) { + pr_err("Cannot insert IOMEM resource [%llx - %llx]\n", + tmp_res->start, tmp_res->end); + kfree(tmp_res); + goto err_insert; + } + } + pgmap = kzalloc(sizeof(*pgmap), GFP_KERNEL); if (!pgmap) { ret = -ENOMEM; @@ -95,12 +137,40 @@ static int fill_list(unsigned int nr_pages) err_memremap: kfree(pgmap); err_pgmap: + if (tmp_res) { + release_resource(tmp_res); + kfree(tmp_res); + } +err_insert: release_resource(res); err_resource: kfree(res); return ret; } +static void unpopulated_init(void) +{ + static bool inited = false; + int ret; + + if (inited) + return; + + /* + * Try to initialize Xen resource the first and fall back to default + * resource if arch doesn't offer one. + */ + ret = arch_xen_unpopulated_init(&xen_resource); + if (!ret) + target_resource = &xen_resource; + else if (ret == -ENOSYS) + target_resource = &iomem_resource; + else + pr_err("Cannot initialize Xen resource\n"); + + inited = true; +} + /** * xen_alloc_unpopulated_pages - alloc unpopulated pages * @nr_pages: Number of pages @@ -112,6 +182,16 @@ int xen_alloc_unpopulated_pages(unsigned int nr_pages, struct page **pages) unsigned int i; int ret = 0; + unpopulated_init(); + + /* + * Fall back to default behavior if we do not have any suitable resource + * to allocate required region from and as the result we won't be able to + * construct pages. + */ + if (!target_resource) + return alloc_xenballooned_pages(nr_pages, pages); + mutex_lock(&list_lock); if (list_count < nr_pages) { ret = fill_list(nr_pages - list_count); @@ -159,6 +239,9 @@ void xen_free_unpopulated_pages(unsigned int nr_pages, struct page **pages) { unsigned int i; + if (!target_resource) + return free_xenballooned_pages(nr_pages, pages); + mutex_lock(&list_lock); for (i = 0; i < nr_pages; i++) { pages[i]->zone_device_data = page_list; diff --git a/include/xen/xen.h b/include/xen/xen.h index 43efba0..55d2ef8 100644 --- a/include/xen/xen.h +++ b/include/xen/xen.h @@ -55,6 +55,8 @@ extern u64 xen_saved_max_mem_size; #ifdef CONFIG_XEN_UNPOPULATED_ALLOC int xen_alloc_unpopulated_pages(unsigned int nr_pages, struct page **pages); void xen_free_unpopulated_pages(unsigned int nr_pages, struct page **pages); +struct resource; +int arch_xen_unpopulated_init(struct resource *res); #else #define xen_alloc_unpopulated_pages alloc_xenballooned_pages #define xen_free_unpopulated_pages free_xenballooned_pages