| Message ID | 20231119165721.9849-7-alexandru.elisei@arm.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | [RFC,v2,01/27] arm64: mte: Rework naming for tag manipulation functions | expand |
On 19.11.23 17:57, Alexandru Elisei wrote: > Add arch_free_pages_prepare() hook that is called before that page flags > are cleared. This will be used by arm64 when explicit management of tag > storage pages is enabled. Can you elaborate a bit what exactly will be done by that code with that information?
Hi, On Fri, Nov 24, 2023 at 08:36:52PM +0100, David Hildenbrand wrote: > On 19.11.23 17:57, Alexandru Elisei wrote: > > Add arch_free_pages_prepare() hook that is called before that page flags > > are cleared. This will be used by arm64 when explicit management of tag > > storage pages is enabled. > > Can you elaborate a bit what exactly will be done by that code with that > information? Of course. The MTE code that is in the kernel today 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() when it does: page->flags &= ~PAGE_FLAGS_CHECK_AT_PREP; When tag storage management is enabled, tag storage is reserved for a page if and only if the page is mapped as tagged. When a page is freed, the code looks at the PG_mte_tagged flag to determine if the page was mapped as tagged, and therefore has tag storage reserved, to determine if the corresponding tag storage should also be freed. I have considered using arch_free_page(), but free_pages_prepare() calls the function after the flags are cleared. Does that answer your question? Alex > > -- > Cheers, > > David / dhildenb >
On 27.11.23 14:03, Alexandru Elisei wrote: > Hi, > > On Fri, Nov 24, 2023 at 08:36:52PM +0100, David Hildenbrand wrote: >> On 19.11.23 17:57, Alexandru Elisei wrote: >>> Add arch_free_pages_prepare() hook that is called before that page flags >>> are cleared. This will be used by arm64 when explicit management of tag >>> storage pages is enabled. >> >> Can you elaborate a bit what exactly will be done by that code with that >> information? > > Of course. > > The MTE code that is in the kernel today 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() when it does: > > page->flags &= ~PAGE_FLAGS_CHECK_AT_PREP; > > When tag storage management is enabled, tag storage is reserved for a page if > and only if the page is mapped as tagged. When a page is freed, the code looks > at the PG_mte_tagged flag to determine if the page was mapped as tagged, and > therefore has tag storage reserved, to determine if the corresponding tag > storage should also be freed. > > I have considered using arch_free_page(), but free_pages_prepare() calls the > function after the flags are cleared. > > Does that answer your question? Yes, please add some of that to the patch description!
Hi, On Tue, Nov 28, 2023 at 05:58:55PM +0100, David Hildenbrand wrote: > On 27.11.23 14:03, Alexandru Elisei wrote: > > Hi, > > > > On Fri, Nov 24, 2023 at 08:36:52PM +0100, David Hildenbrand wrote: > > > On 19.11.23 17:57, Alexandru Elisei wrote: > > > > Add arch_free_pages_prepare() hook that is called before that page flags > > > > are cleared. This will be used by arm64 when explicit management of tag > > > > storage pages is enabled. > > > > > > Can you elaborate a bit what exactly will be done by that code with that > > > information? > > > > Of course. > > > > The MTE code that is in the kernel today 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() when it does: > > > > page->flags &= ~PAGE_FLAGS_CHECK_AT_PREP; > > > > When tag storage management is enabled, tag storage is reserved for a page if > > and only if the page is mapped as tagged. When a page is freed, the code looks > > at the PG_mte_tagged flag to determine if the page was mapped as tagged, and > > therefore has tag storage reserved, to determine if the corresponding tag > > storage should also be freed. > > > > I have considered using arch_free_page(), but free_pages_prepare() calls the > > function after the flags are cleared. > > > > Does that answer your question? > > Yes, please add some of that to the patch description! Will do! Thanks, Alex > > -- > Cheers, > > David / dhildenb >
diff --git a/include/linux/pgtable.h b/include/linux/pgtable.h index b31f53e9ab1d..3f34f00ced62 100644 --- a/include/linux/pgtable.h +++ b/include/linux/pgtable.h @@ -880,6 +880,10 @@ static inline int arch_prep_new_page(struct page *page, int order, gfp_t gfp) } #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 b2782b778e78..86e4b1dac538 100644 --- a/mm/page_alloc.c +++ b/mm/page_alloc.c @@ -1086,6 +1086,8 @@ 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 (unlikely(PageHWPoison(page)) && !order) { /* * Do not let hwpoison pages hit pcplists/buddy @@ -3171,7 +3173,7 @@ static inline unsigned int gfp_to_alloc_flags_cma(gfp_t gfp_mask, return alloc_flags; } -#ifdef HAVE_ARCH_ALLOC_PAGE +#ifdef HAVE_ARCH_PREP_NEW_PAGE static void return_page_to_buddy(struct page *page, int order) { int migratetype = get_pfnblock_migratetype(page, pfn);
Add arch_free_pages_prepare() hook that is called before that page flags are cleared. This will be used by arm64 when explicit management of tag storage pages is enabled. Signed-off-by: Alexandru Elisei <alexandru.elisei@arm.com> --- include/linux/pgtable.h | 4 ++++ mm/page_alloc.c | 4 +++- 2 files changed, 7 insertions(+), 1 deletion(-)