| Message ID | 1627490656-1267-1-git-send-email-olekstysh@gmail.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | [RFC,1/2] arm64: mm: Make virt_addr_valid to check for pfn_valid again | expand |
Adding Mike and Anshuman, On Wed, Jul 28, 2021 at 07:44:15PM +0300, Oleksandr Tyshchenko wrote: > From: Oleksandr Tyshchenko <oleksandr_tyshchenko@epam.com> > > The problem is that Arm's implementation of virt_addr_valid() > leads to memblock_is_map_memory() check, which will fail for > ZONE_DEVICE based addresses. But, the pfn_valid() check in turn > is able to cope with ZONE_DEVICE based memory. > > You can find a good explanation of that problem at: > https://lore.kernel.org/lkml/1614921898-4099-2-git-send-email-anshuman.khandual@arm.com > > Signed-off-by: Oleksandr Tyshchenko <oleksandr_tyshchenko@epam.com> > --- > I am not quite sure whether it is a "correct" place and > the change itself, I just partially restored a behaviour before: > https://lore.kernel.org/lkml/20210511100550.28178-4-rppt@kernel.org > So, the target of this patch is to get a feedback how to resolve > this properly if, of course, this really needs to be resolved > (I might miss important bits here). > > It is worth mentioning that patch doesn't fix the current code base > (if I am not mistaken, no one calls virt_addr_valid() on Arm64 for > ZONE_DEVICE based addresses at the moment, so it seems that nothing > is broken), the fix is intended for the subsequent patch in this > series that will try to enable Xen's "unpopulated-alloc" usage > on Arm (it was enabled on x86 so far). > Please see: > [RFC PATCH 2/2] xen/unpopulated-alloc: Query hypervisor to provide > unallocated space > > The subsequent patch will enable the code where virt_addr_valid() > is used in drivers/xen/unpopulated-alloc.c:fill_list() to check that > a virtual address returned by memremap_pages() is valid. I wonder what the point of calling virt_addr_valid() in fill_list() is? If memremap_pages() succeeded, the pages were mapped at the returned vaddr, there's no need for an additional virt_addr_valid() check. > --- > arch/arm64/include/asm/memory.h | 2 +- > 1 file changed, 1 insertion(+), 1 deletion(-) > > diff --git a/arch/arm64/include/asm/memory.h b/arch/arm64/include/asm/memory.h > index 824a365..1a35a44 100644 > --- a/arch/arm64/include/asm/memory.h > +++ b/arch/arm64/include/asm/memory.h > @@ -351,7 +351,7 @@ static inline void *phys_to_virt(phys_addr_t x) > > #define virt_addr_valid(addr) ({ \ > __typeof__(addr) __addr = __tag_reset(addr); \ > - __is_lm_address(__addr) && pfn_is_map_memory(virt_to_pfn(__addr)); \ > + __is_lm_address(__addr) && pfn_valid(virt_to_pfn(__addr)); \ > }) pfn_valid() only guarantees the presence of a struct page but not necessarily that the virtual address is accessible (valid). So this change would break the NOMAP ranges case.
Hi, On Mon, Aug 02, 2021 at 01:19:48PM +0100, Catalin Marinas wrote: > Adding Mike and Anshuman, > > On Wed, Jul 28, 2021 at 07:44:15PM +0300, Oleksandr Tyshchenko wrote: > > From: Oleksandr Tyshchenko <oleksandr_tyshchenko@epam.com> > > > > The problem is that Arm's implementation of virt_addr_valid() > > leads to memblock_is_map_memory() check, which will fail for > > ZONE_DEVICE based addresses. But, the pfn_valid() check in turn > > is able to cope with ZONE_DEVICE based memory. > > > > You can find a good explanation of that problem at: > > https://lore.kernel.org/lkml/1614921898-4099-2-git-send-email-anshuman.khandual@arm.com > > > > Signed-off-by: Oleksandr Tyshchenko <oleksandr_tyshchenko@epam.com> > > --- > > I am not quite sure whether it is a "correct" place and > > the change itself, I just partially restored a behaviour before: > > https://lore.kernel.org/lkml/20210511100550.28178-4-rppt@kernel.org > > So, the target of this patch is to get a feedback how to resolve > > this properly if, of course, this really needs to be resolved > > (I might miss important bits here). > > > > It is worth mentioning that patch doesn't fix the current code base > > (if I am not mistaken, no one calls virt_addr_valid() on Arm64 for > > ZONE_DEVICE based addresses at the moment, so it seems that nothing > > is broken), the fix is intended for the subsequent patch in this > > series that will try to enable Xen's "unpopulated-alloc" usage > > on Arm (it was enabled on x86 so far). > > Please see: > > [RFC PATCH 2/2] xen/unpopulated-alloc: Query hypervisor to provide > > unallocated space > > > > The subsequent patch will enable the code where virt_addr_valid() > > is used in drivers/xen/unpopulated-alloc.c:fill_list() to check that > > a virtual address returned by memremap_pages() is valid. > I wonder what the point of calling virt_addr_valid() in fill_list() is? > If memremap_pages() succeeded, the pages were mapped at the returned > vaddr, there's no need for an additional virt_addr_valid() check. The virt_addr_valid() check in fill_list() looks bogus to me as well. If memremap_pages() succeeds the range is guaranteed to have proper page table. I believe the first patch should be rather removal of the virt_addr_valid() check in fill_list(). > > --- > > arch/arm64/include/asm/memory.h | 2 +- > > 1 file changed, 1 insertion(+), 1 deletion(-) > > > > diff --git a/arch/arm64/include/asm/memory.h b/arch/arm64/include/asm/memory.h > > index 824a365..1a35a44 100644 > > --- a/arch/arm64/include/asm/memory.h > > +++ b/arch/arm64/include/asm/memory.h > > @@ -351,7 +351,7 @@ static inline void *phys_to_virt(phys_addr_t x) > > > > #define virt_addr_valid(addr) ({ \ > > __typeof__(addr) __addr = __tag_reset(addr); \ > > - __is_lm_address(__addr) && pfn_is_map_memory(virt_to_pfn(__addr)); \ > > + __is_lm_address(__addr) && pfn_valid(virt_to_pfn(__addr)); \ > > }) > > pfn_valid() only guarantees the presence of a struct page but not > necessarily that the virtual address is accessible (valid). So this > change would break the NOMAP ranges case. +1
Hello, all. On 02.08.21 18:08, Mike Rapoport wrote: > Hi, > > On Mon, Aug 02, 2021 at 01:19:48PM +0100, Catalin Marinas wrote: >> Adding Mike and Anshuman, >> >> On Wed, Jul 28, 2021 at 07:44:15PM +0300, Oleksandr Tyshchenko wrote: >>> From: Oleksandr Tyshchenko <oleksandr_tyshchenko@epam.com> >>> >>> The problem is that Arm's implementation of virt_addr_valid() >>> leads to memblock_is_map_memory() check, which will fail for >>> ZONE_DEVICE based addresses. But, the pfn_valid() check in turn >>> is able to cope with ZONE_DEVICE based memory. >>> >>> You can find a good explanation of that problem at: >>> https://lore.kernel.org/lkml/1614921898-4099-2-git-send-email-anshuman.khandual@arm.com >>> >>> Signed-off-by: Oleksandr Tyshchenko <oleksandr_tyshchenko@epam.com> >>> --- >>> I am not quite sure whether it is a "correct" place and >>> the change itself, I just partially restored a behaviour before: >>> https://lore.kernel.org/lkml/20210511100550.28178-4-rppt@kernel.org >>> So, the target of this patch is to get a feedback how to resolve >>> this properly if, of course, this really needs to be resolved >>> (I might miss important bits here). >>> >>> It is worth mentioning that patch doesn't fix the current code base >>> (if I am not mistaken, no one calls virt_addr_valid() on Arm64 for >>> ZONE_DEVICE based addresses at the moment, so it seems that nothing >>> is broken), the fix is intended for the subsequent patch in this >>> series that will try to enable Xen's "unpopulated-alloc" usage >>> on Arm (it was enabled on x86 so far). >>> Please see: >>> [RFC PATCH 2/2] xen/unpopulated-alloc: Query hypervisor to provide >>> unallocated space >>> >>> The subsequent patch will enable the code where virt_addr_valid() >>> is used in drivers/xen/unpopulated-alloc.c:fill_list() to check that >>> a virtual address returned by memremap_pages() is valid. > >> I wonder what the point of calling virt_addr_valid() in fill_list() is? >> If memremap_pages() succeeded, the pages were mapped at the returned >> vaddr, there's no need for an additional virt_addr_valid() check. > The virt_addr_valid() check in fill_list() looks bogus to me as well. If > memremap_pages() succeeds the range is guaranteed to have proper page > table. > > I believe the first patch should be rather removal of the virt_addr_valid() > check in fill_list(). Thank you for the clarification, I will send a patch to remove virt_addr_valid() check in fill_list() for the non-RFC version. > >>> --- >>> arch/arm64/include/asm/memory.h | 2 +- >>> 1 file changed, 1 insertion(+), 1 deletion(-) >>> >>> diff --git a/arch/arm64/include/asm/memory.h b/arch/arm64/include/asm/memory.h >>> index 824a365..1a35a44 100644 >>> --- a/arch/arm64/include/asm/memory.h >>> +++ b/arch/arm64/include/asm/memory.h >>> @@ -351,7 +351,7 @@ static inline void *phys_to_virt(phys_addr_t x) >>> >>> #define virt_addr_valid(addr) ({ \ >>> __typeof__(addr) __addr = __tag_reset(addr); \ >>> - __is_lm_address(__addr) && pfn_is_map_memory(virt_to_pfn(__addr)); \ >>> + __is_lm_address(__addr) && pfn_valid(virt_to_pfn(__addr)); \ >>> }) >> pfn_valid() only guarantees the presence of a struct page but not >> necessarily that the virtual address is accessible (valid). So this >> change would break the NOMAP ranges case. > +1 Oh, I got it.
diff --git a/arch/arm64/include/asm/memory.h b/arch/arm64/include/asm/memory.h index 824a365..1a35a44 100644 --- a/arch/arm64/include/asm/memory.h +++ b/arch/arm64/include/asm/memory.h @@ -351,7 +351,7 @@ static inline void *phys_to_virt(phys_addr_t x) #define virt_addr_valid(addr) ({ \ __typeof__(addr) __addr = __tag_reset(addr); \ - __is_lm_address(__addr) && pfn_is_map_memory(virt_to_pfn(__addr)); \ + __is_lm_address(__addr) && pfn_valid(virt_to_pfn(__addr)); \ }) void dump_mem_limit(void);