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Date: Tue, 30 Jan 2024 11:38:02 +0000
From: Alexandru Elisei <alexandru.elisei@arm.com>
To: Peter Collingbourne <pcc@google.com>
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Subject: Re: [PATCH RFC v3 23/35] arm64: mte: Try to reserve tag storage in
 arch_alloc_page()
Message-ID: <ZbjfmqpYex4C8Uhm@raptor>
References: <20240125164256.4147-1-alexandru.elisei@arm.com>
 <20240125164256.4147-24-alexandru.elisei@arm.com>
 <CAMn1gO5pGVRCErVF+Ca-4JgHRKEcq9sDGyEe--gEjj5ZLrB8sA@mail.gmail.com>
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Hi Peter,

On Mon, Jan 29, 2024 at 04:04:18PM -0800, Peter Collingbourne wrote:
> On Thu, Jan 25, 2024 at 8:45 AM Alexandru Elisei
> <alexandru.elisei@arm.com> wrote:
> >
> > Reserve tag storage for a page that is being allocated as tagged. This
> > is a best effort approach, and failing to reserve tag storage is
> > allowed.
> >
> > When all the associated tagged pages have been freed, return the tag
> > storage pages back to the page allocator, where they can be used again for
> > data allocations.
> >
> > Signed-off-by: Alexandru Elisei <alexandru.elisei@arm.com>
> > ---
> >
> > Changes since rfc v2:
> >
> > * Based on rfc v2 patch #16 ("arm64: mte: Manage tag storage on page
> > allocation").
> > * Fixed calculation of the number of associated tag storage blocks (Hyesoo
> > Yu).
> > * Tag storage is reserved in arch_alloc_page() instead of
> > arch_prep_new_page().
> >
> >  arch/arm64/include/asm/mte.h             |  16 +-
> >  arch/arm64/include/asm/mte_tag_storage.h |  31 +++
> >  arch/arm64/include/asm/page.h            |   5 +
> >  arch/arm64/include/asm/pgtable.h         |  19 ++
> >  arch/arm64/kernel/mte_tag_storage.c      | 234 +++++++++++++++++++++++
> >  arch/arm64/mm/fault.c                    |   7 +
> >  fs/proc/page.c                           |   1 +
> >  include/linux/kernel-page-flags.h        |   1 +
> >  include/linux/page-flags.h               |   1 +
> >  include/trace/events/mmflags.h           |   3 +-
> >  mm/huge_memory.c                         |   1 +
> >  11 files changed, 316 insertions(+), 3 deletions(-)
> >
> > diff --git a/arch/arm64/include/asm/mte.h b/arch/arm64/include/asm/mte.h
> > index 8034695b3dd7..6457b7899207 100644
> > --- a/arch/arm64/include/asm/mte.h
> > +++ b/arch/arm64/include/asm/mte.h
> > @@ -40,12 +40,24 @@ void mte_free_tag_buf(void *buf);
> >  #ifdef CONFIG_ARM64_MTE
> >
> >  /* track which pages have valid allocation tags */
> > -#define PG_mte_tagged  PG_arch_2
> > +#define PG_mte_tagged          PG_arch_2
> >  /* simple lock to avoid multiple threads tagging the same page */
> > -#define PG_mte_lock    PG_arch_3
> > +#define PG_mte_lock            PG_arch_3
> > +/* Track if a tagged page has tag storage reserved */
> > +#define PG_tag_storage_reserved        PG_arch_4
> > +
> > +#ifdef CONFIG_ARM64_MTE_TAG_STORAGE
> > +DECLARE_STATIC_KEY_FALSE(tag_storage_enabled_key);
> > +extern bool page_tag_storage_reserved(struct page *page);
> > +#endif
> >
> >  static inline void set_page_mte_tagged(struct page *page)
> >  {
> > +#ifdef CONFIG_ARM64_MTE_TAG_STORAGE
> > +       /* Open code mte_tag_storage_enabled() */
> > +       WARN_ON_ONCE(static_branch_likely(&tag_storage_enabled_key) &&
> > +                    !page_tag_storage_reserved(page));
> > +#endif
> >         /*
> >          * Ensure that the tags written prior to this function are visible
> >          * before the page flags update.
> > diff --git a/arch/arm64/include/asm/mte_tag_storage.h b/arch/arm64/include/asm/mte_tag_storage.h
> > index 7b3f6bff8e6f..09f1318d924e 100644
> > --- a/arch/arm64/include/asm/mte_tag_storage.h
> > +++ b/arch/arm64/include/asm/mte_tag_storage.h
> > @@ -5,6 +5,12 @@
> >  #ifndef __ASM_MTE_TAG_STORAGE_H
> >  #define __ASM_MTE_TAG_STORAGE_H
> >
> > +#ifndef __ASSEMBLY__
> > +
> > +#include <linux/mm_types.h>
> > +
> > +#include <asm/mte.h>
> > +
> >  #ifdef CONFIG_ARM64_MTE_TAG_STORAGE
> >
> >  DECLARE_STATIC_KEY_FALSE(tag_storage_enabled_key);
> > @@ -15,6 +21,15 @@ static inline bool tag_storage_enabled(void)
> >  }
> >
> >  void mte_init_tag_storage(void);
> > +
> > +static inline bool alloc_requires_tag_storage(gfp_t gfp)
> > +{
> > +       return gfp & __GFP_TAGGED;
> > +}
> > +int reserve_tag_storage(struct page *page, int order, gfp_t gfp);
> > +void free_tag_storage(struct page *page, int order);
> > +
> > +bool page_tag_storage_reserved(struct page *page);
> >  #else
> >  static inline bool tag_storage_enabled(void)
> >  {
> > @@ -23,6 +38,22 @@ static inline bool tag_storage_enabled(void)
> >  static inline void mte_init_tag_storage(void)
> >  {
> >  }
> > +static inline bool alloc_requires_tag_storage(struct page *page)
> 
> This function should take a gfp_t to match the
> CONFIG_ARM64_MTE_TAG_STORAGE case.

Ah, yes, it should, nice catch, the compiler didn't throw an error. Will
fix, thanks!

Alex