Re: [PATCH 02/31] kasan, page_alloc: move tag_clear_highpage out of kernel_init_free_pages

[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, kernel_init_free_pages() serves two purposes: either only
Nit: "it either"

> zeroes memory or zeroes both memory and memory tags via a different
> code path. As this function has only two callers, each using only one
> code path, this behaviour is confusing.
>
> This patch pulls the code that zeroes both memory and tags out of
> kernel_init_free_pages().
>
> As a result of this change, the code in free_pages_prepare() starts to
> look complicated, but this is improved in the few following patches.
> Those improvements are not integrated into this patch to make diffs
> easier to read.
>
> This patch does no functional changes.
>
> Signed-off-by: Andrey Konovalov <andreyknvl@google.com>
Reviewed-by: Alexander Potapenko <glider@google.com>
> ---
>  mm/page_alloc.c | 24 +++++++++++++-----------
>  1 file changed, 13 insertions(+), 11 deletions(-)
>
> diff --git a/mm/page_alloc.c b/mm/page_alloc.c
> index c99566a3b67e..3589333b5b77 100644
> --- a/mm/page_alloc.c
> +++ b/mm/page_alloc.c
> @@ -1269,16 +1269,10 @@ static inline bool should_skip_kasan_poison(struct page *page, fpi_t fpi_flags)
>                PageSkipKASanPoison(page);
>  }
>
> -static void kernel_init_free_pages(struct page *page, int numpages, bool zero_tags)
> +static void kernel_init_free_pages(struct page *page, int numpages)
>  {
>         int i;
>
> -       if (zero_tags) {
> -               for (i = 0; i < numpages; i++)
> -                       tag_clear_highpage(page + i);
> -               return;
> -       }
> -
>         /* s390's use of memset() could override KASAN redzones. */
>         kasan_disable_current();
>         for (i = 0; i < numpages; i++) {
> @@ -1372,7 +1366,7 @@ static __always_inline bool free_pages_prepare(struct page *page,
>                 bool init = want_init_on_free();
>
>                 if (init)
> -                       kernel_init_free_pages(page, 1 << order, false);
> +                       kernel_init_free_pages(page, 1 << order);
>                 if (!skip_kasan_poison)
>                         kasan_poison_pages(page, order, init);
>         }
> @@ -2415,9 +2409,17 @@ inline void post_alloc_hook(struct page *page, unsigned int order,
>                 bool init = !want_init_on_free() && want_init_on_alloc(gfp_flags);
>
>                 kasan_unpoison_pages(page, order, init);
> -               if (init)
> -                       kernel_init_free_pages(page, 1 << order,
> -                                              gfp_flags & __GFP_ZEROTAGS);
> +
> +               if (init) {
> +                       if (gfp_flags & __GFP_ZEROTAGS) {
> +                               int i;
> +
> +                               for (i = 0; i < 1 << order; i++)
> +                                       tag_clear_highpage(page + i);
> +                       } else {
> +                               kernel_init_free_pages(page, 1 << order);
> +                       }
> +               }
>         }
>
>         set_page_owner(page, order, gfp_flags);
> --
> 2.25.1
>
> --
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-- 
Alexander Potapenko
Software Engineer

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