| Message ID | 20240524124055.3871399-4-luca.fancellu@arm.com (mailing list archive) |
|---|---|
| State | New |
| Headers | show |
| Series | Static shared memory followup v2 - pt2 | expand |
Hi Luca, On 24/05/2024 13:40, Luca Fancellu wrote: > From: Penny Zheng <Penny.Zheng@arm.com> > > We are doing foreign memory mapping for static shared memory, and > there is a great possibility that it could be super mapped. > But today, p2m_put_l3_page could not handle superpages. > > This commits implements a new function p2m_put_l2_superpage to handle > 2MB superpages, specifically for helping put extra references for > foreign superpages. > > Modify relinquish_p2m_mapping as well to take into account preemption > when type is foreign memory and order is above 9 (2MB). > > Currently 1GB superpages are not handled because Xen is not preemptible > and therefore some work is needed to handle such superpages, for which > at some point Xen might end up freeing memory and therefore for such a > big mapping it could end up in a very long operation. > > Signed-off-by: Penny Zheng <penny.zheng@arm.com> > Signed-off-by: Luca Fancellu <luca.fancellu@arm.com> > --- > v4 changes: > - optimised the path to call put_page() on the foreign mapping as > Julien suggested. Add a comment in p2m_put_l2_superpage to state > that any changes needs to take into account some change in the > relinquish code. (Julien) > v3 changes: > - Add reasoning why we don't support now 1GB superpage, remove level_order > variable from p2m_put_l2_superpage, update TODO comment inside > p2m_free_entry, use XEN_PT_LEVEL_ORDER(2) instead of value 9 inside > relinquish_p2m_mapping. (Michal) > v2: > - Do not handle 1GB super page as there might be some issue where > a lot of calls to put_page(...) might be issued which could lead > to free memory that is a long operation. > v1: > - patch from https://patchwork.kernel.org/project/xen-devel/patch/20231206090623.1932275-9-Penny.Zheng@arm.com/ > --- > xen/arch/arm/mmu/p2m.c | 82 +++++++++++++++++++++++++++++++----------- > 1 file changed, 62 insertions(+), 20 deletions(-) > > diff --git a/xen/arch/arm/mmu/p2m.c b/xen/arch/arm/mmu/p2m.c > index 41fcca011cf4..986c5a03c54b 100644 > --- a/xen/arch/arm/mmu/p2m.c > +++ b/xen/arch/arm/mmu/p2m.c > @@ -753,34 +753,66 @@ static int p2m_mem_access_radix_set(struct p2m_domain *p2m, gfn_t gfn, > return rc; > } > > -/* > - * Put any references on the single 4K page referenced by pte. > - * TODO: Handle superpages, for now we only take special references for leaf > - * pages (specifically foreign ones, which can't be super mapped today). > - */ > -static void p2m_put_l3_page(const lpae_t pte) > +static void p2m_put_foreign_page(struct page_info *pg) > { > - mfn_t mfn = lpae_get_mfn(pte); > - > - ASSERT(p2m_is_valid(pte)); > - > /* > - * TODO: Handle other p2m types > - * > * It's safe to do the put_page here because page_alloc will > * flush the TLBs if the page is reallocated before the end of > * this loop. > */ > - if ( p2m_is_foreign(pte.p2m.type) ) > + put_page(pg); > +} > + > +/* Put any references on the single 4K page referenced by mfn. */ > +static void p2m_put_l3_page(mfn_t mfn, p2m_type_t type) > +{ > + /* TODO: Handle other p2m types */ > + if ( p2m_is_foreign(type) ) > { > ASSERT(mfn_valid(mfn)); > - put_page(mfn_to_page(mfn)); > + p2m_put_foreign_page(mfn_to_page(mfn)); > } > /* Detect the xenheap page and mark the stored GFN as invalid. */ > - else if ( p2m_is_ram(pte.p2m.type) && is_xen_heap_mfn(mfn) ) > + else if ( p2m_is_ram(type) && is_xen_heap_mfn(mfn) ) > page_set_xenheap_gfn(mfn_to_page(mfn), INVALID_GFN); > } > > +/* Put any references on the superpage referenced by mfn. */ > +static void p2m_put_l2_superpage(mfn_t mfn, p2m_type_t type) > +{ > + struct page_info *pg; > + unsigned int i; > + > + /* > + * TODO: Handle other p2m types, but be aware that any changes to handle > + * different types should require an update on the relinquish code to handle > + * preemption. > + */ > + if ( !p2m_is_foreign(type) ) > + return; > + > + ASSERT(mfn_valid(mfn)); > + > + pg = mfn_to_page(mfn); > + > + for ( i = 0; i < XEN_PT_LPAE_ENTRIES; i++, pg++ ) > + p2m_put_foreign_page(pg); > +} > + > +/* Put any references on the page referenced by pte. */ > +static void p2m_put_page(const lpae_t pte, unsigned int level) > +{ > + mfn_t mfn = lpae_get_mfn(pte); > + > + ASSERT(p2m_is_valid(pte)); > + > + /* We have a second level 2M superpage */ > + if ( p2m_is_superpage(pte, level) && (level == 2) ) AFAICT, p2m_put_page() can only be called if the pte points to a superpage or page: if ( p2m_is_superpage(entry, level) || (level == 3) ) { ... p2m_put_page() } So do we actually need to check p2m_is_superpage()? > + return p2m_put_l2_superpage(mfn, pte.p2m.type); > + else if ( level == 3 ) > + return p2m_put_l3_page(mfn, pte.p2m.type); > +} > + > /* Free lpae sub-tree behind an entry */ > static void p2m_free_entry(struct p2m_domain *p2m, > lpae_t entry, unsigned int level) > @@ -809,9 +841,16 @@ static void p2m_free_entry(struct p2m_domain *p2m, > #endif > > p2m->stats.mappings[level]--; > - /* Nothing to do if the entry is a super-page. */ > - if ( level == 3 ) > - p2m_put_l3_page(entry); > + /* > + * TODO: Currently we don't handle 1GB super-page, Xen is not > + * preemptible and therefore some work is needed to handle such > + * superpages, for which at some point Xen might end up freeing memory > + * and therefore for such a big mapping it could end up in a very long > + * operation. > + */ > + if ( level >= 2 ) The code in p2m_put_page() can properly handle level 1. So I would rather prefer if we remove this check (again in order to reduce the amount of work in the P2M code). This TODO could be moved there. > + p2m_put_page(entry, level); > + > return; > } > > @@ -1558,9 +1597,12 @@ int relinquish_p2m_mapping(struct domain *d) > > count++; > /* > - * Arbitrarily preempt every 512 iterations. > + * Arbitrarily preempt every 512 iterations or when type is foreign > + * mapping and the order is above 9 (2MB). Let's avoid mentioning 2MB. This is only valid when using 4KB pages. This is also talking about a specific when the code below is not 4KB specific. I would rework anything after the 'or' to: 'we have a level-2 foreign mapping' The rest of the LGTM to me but I don't feel confortable to do all those changes on commit. So this will want a respin. For simplicity, you can only resend this patch. Cheers,
Hi Julien, > On 24 May 2024, at 13:56, Julien Grall <julien@xen.org> wrote: > > Hi Luca, > > On 24/05/2024 13:40, Luca Fancellu wrote: >> From: Penny Zheng <Penny.Zheng@arm.com> >> We are doing foreign memory mapping for static shared memory, and >> there is a great possibility that it could be super mapped. >> But today, p2m_put_l3_page could not handle superpages. >> This commits implements a new function p2m_put_l2_superpage to handle >> 2MB superpages, specifically for helping put extra references for >> foreign superpages. >> Modify relinquish_p2m_mapping as well to take into account preemption >> when type is foreign memory and order is above 9 (2MB). >> Currently 1GB superpages are not handled because Xen is not preemptible >> and therefore some work is needed to handle such superpages, for which >> at some point Xen might end up freeing memory and therefore for such a >> big mapping it could end up in a very long operation. >> Signed-off-by: Penny Zheng <penny.zheng@arm.com> >> Signed-off-by: Luca Fancellu <luca.fancellu@arm.com> >> --- >> v4 changes: >> - optimised the path to call put_page() on the foreign mapping as >> Julien suggested. Add a comment in p2m_put_l2_superpage to state >> that any changes needs to take into account some change in the >> relinquish code. (Julien) >> v3 changes: >> - Add reasoning why we don't support now 1GB superpage, remove level_order >> variable from p2m_put_l2_superpage, update TODO comment inside >> p2m_free_entry, use XEN_PT_LEVEL_ORDER(2) instead of value 9 inside >> relinquish_p2m_mapping. (Michal) >> v2: >> - Do not handle 1GB super page as there might be some issue where >> a lot of calls to put_page(...) might be issued which could lead >> to free memory that is a long operation. >> v1: >> - patch from https://patchwork.kernel.org/project/xen-devel/patch/20231206090623.1932275-9-Penny.Zheng@arm.com/ >> --- >> xen/arch/arm/mmu/p2m.c | 82 +++++++++++++++++++++++++++++++----------- >> 1 file changed, 62 insertions(+), 20 deletions(-) >> diff --git a/xen/arch/arm/mmu/p2m.c b/xen/arch/arm/mmu/p2m.c >> index 41fcca011cf4..986c5a03c54b 100644 >> --- a/xen/arch/arm/mmu/p2m.c >> +++ b/xen/arch/arm/mmu/p2m.c >> @@ -753,34 +753,66 @@ static int p2m_mem_access_radix_set(struct p2m_domain *p2m, gfn_t gfn, >> return rc; >> } >> -/* >> - * Put any references on the single 4K page referenced by pte. >> - * TODO: Handle superpages, for now we only take special references for leaf >> - * pages (specifically foreign ones, which can't be super mapped today). >> - */ >> -static void p2m_put_l3_page(const lpae_t pte) >> +static void p2m_put_foreign_page(struct page_info *pg) >> { >> - mfn_t mfn = lpae_get_mfn(pte); >> - >> - ASSERT(p2m_is_valid(pte)); >> - >> /* >> - * TODO: Handle other p2m types >> - * >> * It's safe to do the put_page here because page_alloc will >> * flush the TLBs if the page is reallocated before the end of >> * this loop. >> */ >> - if ( p2m_is_foreign(pte.p2m.type) ) >> + put_page(pg); >> +} >> + >> +/* Put any references on the single 4K page referenced by mfn. */ >> +static void p2m_put_l3_page(mfn_t mfn, p2m_type_t type) >> +{ >> + /* TODO: Handle other p2m types */ >> + if ( p2m_is_foreign(type) ) >> { >> ASSERT(mfn_valid(mfn)); >> - put_page(mfn_to_page(mfn)); >> + p2m_put_foreign_page(mfn_to_page(mfn)); >> } >> /* Detect the xenheap page and mark the stored GFN as invalid. */ >> - else if ( p2m_is_ram(pte.p2m.type) && is_xen_heap_mfn(mfn) ) >> + else if ( p2m_is_ram(type) && is_xen_heap_mfn(mfn) ) >> page_set_xenheap_gfn(mfn_to_page(mfn), INVALID_GFN); >> } >> +/* Put any references on the superpage referenced by mfn. */ >> +static void p2m_put_l2_superpage(mfn_t mfn, p2m_type_t type) >> +{ >> + struct page_info *pg; >> + unsigned int i; >> + >> + /* >> + * TODO: Handle other p2m types, but be aware that any changes to handle >> + * different types should require an update on the relinquish code to handle >> + * preemption. >> + */ >> + if ( !p2m_is_foreign(type) ) >> + return; >> + >> + ASSERT(mfn_valid(mfn)); >> + >> + pg = mfn_to_page(mfn); >> + >> + for ( i = 0; i < XEN_PT_LPAE_ENTRIES; i++, pg++ ) >> + p2m_put_foreign_page(pg); >> +} >> + >> +/* Put any references on the page referenced by pte. */ >> +static void p2m_put_page(const lpae_t pte, unsigned int level) >> +{ >> + mfn_t mfn = lpae_get_mfn(pte); >> + >> + ASSERT(p2m_is_valid(pte)); >> + >> + /* We have a second level 2M superpage */ >> + if ( p2m_is_superpage(pte, level) && (level == 2) ) > > AFAICT, p2m_put_page() can only be called if the pte points to a superpage or page: > > if ( p2m_is_superpage(entry, level) || (level == 3) ) > { > ... > p2m_put_page() > > } > > So do we actually need to check p2m_is_superpage()? > >> + return p2m_put_l2_superpage(mfn, pte.p2m.type); >> + else if ( level == 3 ) >> + return p2m_put_l3_page(mfn, pte.p2m.type); >> +} >> + >> /* Free lpae sub-tree behind an entry */ >> static void p2m_free_entry(struct p2m_domain *p2m, >> lpae_t entry, unsigned int level) >> @@ -809,9 +841,16 @@ static void p2m_free_entry(struct p2m_domain *p2m, >> #endif >> p2m->stats.mappings[level]--; >> - /* Nothing to do if the entry is a super-page. */ >> - if ( level == 3 ) >> - p2m_put_l3_page(entry); >> + /* >> + * TODO: Currently we don't handle 1GB super-page, Xen is not >> + * preemptible and therefore some work is needed to handle such >> + * superpages, for which at some point Xen might end up freeing memory >> + * and therefore for such a big mapping it could end up in a very long >> + * operation. >> + */ >> + if ( level >= 2 ) > > The code in p2m_put_page() can properly handle level 1. So I would rather prefer if we remove this check (again in order to reduce the amount of work in the P2M code). > > This TODO could be moved there. > >> + p2m_put_page(entry, level); >> + >> return; >> } >> @@ -1558,9 +1597,12 @@ int relinquish_p2m_mapping(struct domain *d) >> count++; >> /* >> - * Arbitrarily preempt every 512 iterations. >> + * Arbitrarily preempt every 512 iterations or when type is foreign >> + * mapping and the order is above 9 (2MB). > > Let's avoid mentioning 2MB. This is only valid when using 4KB pages. > > This is also talking about a specific when the code below is not 4KB specific. I would rework anything after the 'or' to: > > 'we have a level-2 foreign mapping' > > The rest of the LGTM to me but I don't feel confortable to do all those changes on commit. So this will want a respin. > > For simplicity, you can only resend this patch. Thanks, I’ll address your comment and push the new patch asap. Cheers, Luca
diff --git a/xen/arch/arm/mmu/p2m.c b/xen/arch/arm/mmu/p2m.c index 41fcca011cf4..986c5a03c54b 100644 --- a/xen/arch/arm/mmu/p2m.c +++ b/xen/arch/arm/mmu/p2m.c @@ -753,34 +753,66 @@ static int p2m_mem_access_radix_set(struct p2m_domain *p2m, gfn_t gfn, return rc; } -/* - * Put any references on the single 4K page referenced by pte. - * TODO: Handle superpages, for now we only take special references for leaf - * pages (specifically foreign ones, which can't be super mapped today). - */ -static void p2m_put_l3_page(const lpae_t pte) +static void p2m_put_foreign_page(struct page_info *pg) { - mfn_t mfn = lpae_get_mfn(pte); - - ASSERT(p2m_is_valid(pte)); - /* - * TODO: Handle other p2m types - * * It's safe to do the put_page here because page_alloc will * flush the TLBs if the page is reallocated before the end of * this loop. */ - if ( p2m_is_foreign(pte.p2m.type) ) + put_page(pg); +} + +/* Put any references on the single 4K page referenced by mfn. */ +static void p2m_put_l3_page(mfn_t mfn, p2m_type_t type) +{ + /* TODO: Handle other p2m types */ + if ( p2m_is_foreign(type) ) { ASSERT(mfn_valid(mfn)); - put_page(mfn_to_page(mfn)); + p2m_put_foreign_page(mfn_to_page(mfn)); } /* Detect the xenheap page and mark the stored GFN as invalid. */ - else if ( p2m_is_ram(pte.p2m.type) && is_xen_heap_mfn(mfn) ) + else if ( p2m_is_ram(type) && is_xen_heap_mfn(mfn) ) page_set_xenheap_gfn(mfn_to_page(mfn), INVALID_GFN); } +/* Put any references on the superpage referenced by mfn. */ +static void p2m_put_l2_superpage(mfn_t mfn, p2m_type_t type) +{ + struct page_info *pg; + unsigned int i; + + /* + * TODO: Handle other p2m types, but be aware that any changes to handle + * different types should require an update on the relinquish code to handle + * preemption. + */ + if ( !p2m_is_foreign(type) ) + return; + + ASSERT(mfn_valid(mfn)); + + pg = mfn_to_page(mfn); + + for ( i = 0; i < XEN_PT_LPAE_ENTRIES; i++, pg++ ) + p2m_put_foreign_page(pg); +} + +/* Put any references on the page referenced by pte. */ +static void p2m_put_page(const lpae_t pte, unsigned int level) +{ + mfn_t mfn = lpae_get_mfn(pte); + + ASSERT(p2m_is_valid(pte)); + + /* We have a second level 2M superpage */ + if ( p2m_is_superpage(pte, level) && (level == 2) ) + return p2m_put_l2_superpage(mfn, pte.p2m.type); + else if ( level == 3 ) + return p2m_put_l3_page(mfn, pte.p2m.type); +} + /* Free lpae sub-tree behind an entry */ static void p2m_free_entry(struct p2m_domain *p2m, lpae_t entry, unsigned int level) @@ -809,9 +841,16 @@ static void p2m_free_entry(struct p2m_domain *p2m, #endif p2m->stats.mappings[level]--; - /* Nothing to do if the entry is a super-page. */ - if ( level == 3 ) - p2m_put_l3_page(entry); + /* + * TODO: Currently we don't handle 1GB super-page, Xen is not + * preemptible and therefore some work is needed to handle such + * superpages, for which at some point Xen might end up freeing memory + * and therefore for such a big mapping it could end up in a very long + * operation. + */ + if ( level >= 2 ) + p2m_put_page(entry, level); + return; } @@ -1558,9 +1597,12 @@ int relinquish_p2m_mapping(struct domain *d) count++; /* - * Arbitrarily preempt every 512 iterations. + * Arbitrarily preempt every 512 iterations or when type is foreign + * mapping and the order is above 9 (2MB). */ - if ( !(count % 512) && hypercall_preempt_check() ) + if ( (!(count % 512) || + (p2m_is_foreign(t) && (order > XEN_PT_LEVEL_ORDER(2)))) && + hypercall_preempt_check() ) { rc = -ERESTART; break;