[PATCH v5 3/7] init_on_alloc: Unpessimize default-on builds

[Andrey Konovalov]

On Tue, Mar 9, 2021 at 10:43 PM Kees Cook <keescook at chromium.org> wrote:
>
> Right now, the state of CONFIG_INIT_ON_ALLOC_DEFAULT_ON (and
> ...ON_FREE...) did not change the assembly ordering of the static branch
> tests. Use the new jump_label macro to check CONFIG settings to default
> to the "expected" state, unpessimizes the resulting assembly code.
>
> Reviewed-by: Alexander Potapenko <glider at google.com>
> Link: https://lore.kernel.org/lkml/CAG_fn=X0DVwqLaHJTO6Jw7TGcMSm77GKHinrd0m_6y0SzWOrFA@mail.gmail.com/
> Signed-off-by: Kees Cook <keescook at chromium.org>
> ---
>  include/linux/mm.h | 6 ++++--
>  1 file changed, 4 insertions(+), 2 deletions(-)
>
> diff --git a/include/linux/mm.h b/include/linux/mm.h
> index bf341a9bfe46..2ccd856ac0d1 100644
> --- a/include/linux/mm.h
> +++ b/include/linux/mm.h
> @@ -2874,7 +2874,8 @@ static inline void kernel_unpoison_pages(struct page *page, int numpages) { }
>  DECLARE_STATIC_KEY_MAYBE(CONFIG_INIT_ON_ALLOC_DEFAULT_ON, init_on_alloc);
>  static inline bool want_init_on_alloc(gfp_t flags)
>  {
> -       if (static_branch_unlikely(&init_on_alloc))
> +       if (static_branch_maybe(CONFIG_INIT_ON_ALLOC_DEFAULT_ON,
> +                               &init_on_alloc))
>                 return true;
>         return flags & __GFP_ZERO;
>  }
> @@ -2882,7 +2883,8 @@ static inline bool want_init_on_alloc(gfp_t flags)
>  DECLARE_STATIC_KEY_MAYBE(CONFIG_INIT_ON_FREE_DEFAULT_ON, init_on_free);
>  static inline bool want_init_on_free(void)
>  {
> -       return static_branch_unlikely(&init_on_free);
> +       return static_branch_maybe(CONFIG_INIT_ON_FREE_DEFAULT_ON,
> +                                  &init_on_free);
>  }
>
>  extern bool _debug_pagealloc_enabled_early;

Should we also update slab_want_init_on_alloc() and slab_want_init_on_free()?