Re: [PATCH 03/31] kasan, page_alloc: merge kasan_free_pages into free_pages_prepare

[Alexander Potapenko <glider@google.com>]

On Tue, Nov 30, 2021 at 10:40 PM <andrey.konovalov@linux.dev> wrote:
>
> From: Andrey Konovalov <andreyknvl@google.com>
>
> Currently, the code responsible for initializing and poisoning memory
> in free_pages_prepare() is scattered across two locations:
> kasan_free_pages() for HW_TAGS KASAN and free_pages_prepare() itself.
> This is confusing.
>
> This and a few following patches combine the code from these two
> locations. Along the way, these patches also simplify the performed
> checks to make them easier to follow.
>
> This patch replaces the only caller of kasan_free_pages() with its
> implementation.
>
> As kasan_has_integrated_init() is only true when CONFIG_KASAN_HW_TAGS
> is enabled, moving the code does no functional changes.
>
> This patch is not useful by itself but makes the simplifications in
> the following patches easier to follow.
>
> Signed-off-by: Andrey Konovalov <andreyknvl@google.com>
Reviewed-by: Alexander Potapenko <glider@google.com>

> ---
>  include/linux/kasan.h |  8 --------
>  mm/kasan/common.c     |  2 +-
>  mm/kasan/hw_tags.c    | 11 -----------
>  mm/page_alloc.c       |  6 ++++--
>  4 files changed, 5 insertions(+), 22 deletions(-)
>
> diff --git a/include/linux/kasan.h b/include/linux/kasan.h
> index d8783b682669..89a43d8ae4fe 100644
> --- a/include/linux/kasan.h
> +++ b/include/linux/kasan.h
> @@ -95,7 +95,6 @@ static inline bool kasan_hw_tags_enabled(void)
>  }
>
>  void kasan_alloc_pages(struct page *page, unsigned int order, gfp_t flags);
> -void kasan_free_pages(struct page *page, unsigned int order);
>
>  #else /* CONFIG_KASAN_HW_TAGS */
>
> @@ -116,13 +115,6 @@ static __always_inline void kasan_alloc_pages(struct page *page,
>         BUILD_BUG();
>  }
>
> -static __always_inline void kasan_free_pages(struct page *page,
> -                                            unsigned int order)
> -{
> -       /* Only available for integrated init. */
> -       BUILD_BUG();
> -}
> -
>  #endif /* CONFIG_KASAN_HW_TAGS */
>
>  static inline bool kasan_has_integrated_init(void)
> diff --git a/mm/kasan/common.c b/mm/kasan/common.c
> index 8428da2aaf17..66078cc1b4f0 100644
> --- a/mm/kasan/common.c
> +++ b/mm/kasan/common.c
> @@ -387,7 +387,7 @@ static inline bool ____kasan_kfree_large(void *ptr, unsigned long ip)
>         }
>
>         /*
> -        * The object will be poisoned by kasan_free_pages() or
> +        * The object will be poisoned by kasan_poison_pages() or
>          * kasan_slab_free_mempool().
>          */
>
> diff --git a/mm/kasan/hw_tags.c b/mm/kasan/hw_tags.c
> index 7355cb534e4f..0b8225add2e4 100644
> --- a/mm/kasan/hw_tags.c
> +++ b/mm/kasan/hw_tags.c
> @@ -213,17 +213,6 @@ void kasan_alloc_pages(struct page *page, unsigned int order, gfp_t flags)
>         }
>  }
>
> -void kasan_free_pages(struct page *page, unsigned int order)
> -{
> -       /*
> -        * This condition should match the one in free_pages_prepare() in
> -        * page_alloc.c.
> -        */
> -       bool init = want_init_on_free();
> -
> -       kasan_poison_pages(page, order, init);
> -}
> -
>  #if IS_ENABLED(CONFIG_KASAN_KUNIT_TEST)
>
>  void kasan_enable_tagging_sync(void)
> diff --git a/mm/page_alloc.c b/mm/page_alloc.c
> index 3589333b5b77..3f3ea41f8c64 100644
> --- a/mm/page_alloc.c
> +++ b/mm/page_alloc.c
> @@ -1353,15 +1353,17 @@ static __always_inline bool free_pages_prepare(struct page *page,
>
>         /*
>          * As memory initialization might be integrated into KASAN,
> -        * kasan_free_pages and kernel_init_free_pages must be
> +        * KASAN poisoning and memory initialization code must be
>          * kept together to avoid discrepancies in behavior.
>          *
>          * With hardware tag-based KASAN, memory tags must be set before the
>          * page becomes unavailable via debug_pagealloc or arch_free_page.
>          */
>         if (kasan_has_integrated_init()) {
> +               bool init = want_init_on_free();
> +
>                 if (!skip_kasan_poison)
> -                       kasan_free_pages(page, order);
> +                       kasan_poison_pages(page, order, init);
>         } else {
>                 bool init = want_init_on_free();
>
> --
> 2.25.1
>
> --
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-- 
Alexander Potapenko
Software Engineer

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