| Message ID | 20240125164256.4147-3-alexandru.elisei@arm.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | Add support for arm64 MTE dynamic tag storage reuse | expand |
On 1/25/24 22:12, Alexandru Elisei wrote: > The arm64 MTE code uses the PG_arch_2 page flag, which it renames to > PG_mte_tagged, to track if a page has been mapped with tagging enabled. > That flag is cleared by free_pages_prepare() by doing: > > page->flags &= ~PAGE_FLAGS_CHECK_AT_PREP; > > When tag storage management is added, tag storage will be reserved for a > page if and only if the page is mapped as tagged (the page flag > PG_mte_tagged is set). When a page is freed, likewise, the code will have > to look at the the page flags to determine if the page has tag storage > reserved, which should also be freed. > > For this purpose, add an arch_free_pages_prepare() hook that is called > before that page flags are cleared. The function arch_free_page() has also > been considered for this purpose, but it is called after the flags are > cleared. arch_free_pages_prepare() makes sense as a prologue to arch_free_page(). s/arch_free_pages_prepare/arch_free_page_prepare to match similar functions. > > Signed-off-by: Alexandru Elisei <alexandru.elisei@arm.com> > --- > > Changes since rfc v2: > > * Expanded commit message (David Hildenbrand). > > include/linux/pgtable.h | 4 ++++ > mm/page_alloc.c | 1 + > 2 files changed, 5 insertions(+) > > diff --git a/include/linux/pgtable.h b/include/linux/pgtable.h > index f6d0e3513948..6d98d5fdd697 100644 > --- a/include/linux/pgtable.h > +++ b/include/linux/pgtable.h > @@ -901,6 +901,10 @@ static inline void arch_do_swap_page(struct mm_struct *mm, > } > #endif > > +#ifndef __HAVE_ARCH_FREE_PAGES_PREPARE I guess new __HAVE_ARCH_ constructs are not being added lately. Instead something like '#ifndef arch_free_pages_prepare' might be better suited. > +static inline void arch_free_pages_prepare(struct page *page, int order) { } > +#endif > + > #ifndef __HAVE_ARCH_UNMAP_ONE > /* > * Some architectures support metadata associated with a page. When a > diff --git a/mm/page_alloc.c b/mm/page_alloc.c > index 2c140abe5ee6..27282a1c82fe 100644 > --- a/mm/page_alloc.c > +++ b/mm/page_alloc.c > @@ -1092,6 +1092,7 @@ static __always_inline bool free_pages_prepare(struct page *page, > > trace_mm_page_free(page, order); > kmsan_free_page(page, order); > + arch_free_pages_prepare(page, order); > > if (memcg_kmem_online() && PageMemcgKmem(page)) > __memcg_kmem_uncharge_page(page, order);
Hi, On Mon, Jan 29, 2024 at 01:49:44PM +0530, Anshuman Khandual wrote: > > > On 1/25/24 22:12, Alexandru Elisei wrote: > > The arm64 MTE code uses the PG_arch_2 page flag, which it renames to > > PG_mte_tagged, to track if a page has been mapped with tagging enabled. > > That flag is cleared by free_pages_prepare() by doing: > > > > page->flags &= ~PAGE_FLAGS_CHECK_AT_PREP; > > > > When tag storage management is added, tag storage will be reserved for a > > page if and only if the page is mapped as tagged (the page flag > > PG_mte_tagged is set). When a page is freed, likewise, the code will have > > to look at the the page flags to determine if the page has tag storage > > reserved, which should also be freed. > > > > For this purpose, add an arch_free_pages_prepare() hook that is called > > before that page flags are cleared. The function arch_free_page() has also > > been considered for this purpose, but it is called after the flags are > > cleared. > > arch_free_pages_prepare() makes sense as a prologue to arch_free_page(). Thanks! > > s/arch_free_pages_prepare/arch_free_page_prepare to match similar functions. The function free_pages_prepare() calls the function arch_free_pages_prepare(). I find that consistent, and it makes it easy to identify from where arch_free_pages_prepare() is called. Thanks, Alex > > > > > Signed-off-by: Alexandru Elisei <alexandru.elisei@arm.com> > > --- > > > > Changes since rfc v2: > > > > * Expanded commit message (David Hildenbrand). > > > > include/linux/pgtable.h | 4 ++++ > > mm/page_alloc.c | 1 + > > 2 files changed, 5 insertions(+) > > > > diff --git a/include/linux/pgtable.h b/include/linux/pgtable.h > > index f6d0e3513948..6d98d5fdd697 100644 > > --- a/include/linux/pgtable.h > > +++ b/include/linux/pgtable.h > > @@ -901,6 +901,10 @@ static inline void arch_do_swap_page(struct mm_struct *mm, > > } > > #endif > > > > +#ifndef __HAVE_ARCH_FREE_PAGES_PREPARE > > I guess new __HAVE_ARCH_ constructs are not being added lately. Instead > something like '#ifndef arch_free_pages_prepare' might be better suited. > > > +static inline void arch_free_pages_prepare(struct page *page, int order) { } > > +#endif > > + > > #ifndef __HAVE_ARCH_UNMAP_ONE > > /* > > * Some architectures support metadata associated with a page. When a > > diff --git a/mm/page_alloc.c b/mm/page_alloc.c > > index 2c140abe5ee6..27282a1c82fe 100644 > > --- a/mm/page_alloc.c > > +++ b/mm/page_alloc.c > > @@ -1092,6 +1092,7 @@ static __always_inline bool free_pages_prepare(struct page *page, > > > > trace_mm_page_free(page, order); > > kmsan_free_page(page, order); > > + arch_free_pages_prepare(page, order); > > > > if (memcg_kmem_online() && PageMemcgKmem(page)) > > __memcg_kmem_uncharge_page(page, order);
diff --git a/include/linux/pgtable.h b/include/linux/pgtable.h index f6d0e3513948..6d98d5fdd697 100644 --- a/include/linux/pgtable.h +++ b/include/linux/pgtable.h @@ -901,6 +901,10 @@ static inline void arch_do_swap_page(struct mm_struct *mm, } #endif +#ifndef __HAVE_ARCH_FREE_PAGES_PREPARE +static inline void arch_free_pages_prepare(struct page *page, int order) { } +#endif + #ifndef __HAVE_ARCH_UNMAP_ONE /* * Some architectures support metadata associated with a page. When a diff --git a/mm/page_alloc.c b/mm/page_alloc.c index 2c140abe5ee6..27282a1c82fe 100644 --- a/mm/page_alloc.c +++ b/mm/page_alloc.c @@ -1092,6 +1092,7 @@ static __always_inline bool free_pages_prepare(struct page *page, trace_mm_page_free(page, order); kmsan_free_page(page, order); + arch_free_pages_prepare(page, order); if (memcg_kmem_online() && PageMemcgKmem(page)) __memcg_kmem_uncharge_page(page, order);
The arm64 MTE code uses the PG_arch_2 page flag, which it renames to PG_mte_tagged, to track if a page has been mapped with tagging enabled. That flag is cleared by free_pages_prepare() by doing: page->flags &= ~PAGE_FLAGS_CHECK_AT_PREP; When tag storage management is added, tag storage will be reserved for a page if and only if the page is mapped as tagged (the page flag PG_mte_tagged is set). When a page is freed, likewise, the code will have to look at the the page flags to determine if the page has tag storage reserved, which should also be freed. For this purpose, add an arch_free_pages_prepare() hook that is called before that page flags are cleared. The function arch_free_page() has also been considered for this purpose, but it is called after the flags are cleared. Signed-off-by: Alexandru Elisei <alexandru.elisei@arm.com> --- Changes since rfc v2: * Expanded commit message (David Hildenbrand). include/linux/pgtable.h | 4 ++++ mm/page_alloc.c | 1 + 2 files changed, 5 insertions(+)