Re: [PATCH RFC v2 09/21] kasan: inline kasan_reset_tag for tag-based modes

[Dmitry Vyukov]

On Thu, Oct 22, 2020 at 3:19 PM Andrey Konovalov <andreyknvl@xxxxxxxxxx> wrote:
>
> Using kasan_reset_tag() currently results in a function call. As it's
> called quite often from the allocator code this leads to a noticeable
> slowdown. Move it to include/linux/kasan.h and turn it into a static
> inline function.
>
> Signed-off-by: Andrey Konovalov <andreyknvl@xxxxxxxxxx>
> Link: https://linux-review.googlesource.com/id/I4d2061acfe91d480a75df00b07c22d8494ef14b5
> ---
>  include/linux/kasan.h | 5 ++++-
>  mm/kasan/hw_tags.c    | 5 -----
>  mm/kasan/kasan.h      | 6 ++----
>  mm/kasan/sw_tags.c    | 5 -----
>  4 files changed, 6 insertions(+), 15 deletions(-)
>
> diff --git a/include/linux/kasan.h b/include/linux/kasan.h
> index 93d9834b7122..6377d7d3a951 100644
> --- a/include/linux/kasan.h
> +++ b/include/linux/kasan.h
> @@ -187,7 +187,10 @@ static inline void kasan_record_aux_stack(void *ptr) {}
>
>  void __init kasan_init_tags(void);
>
> -void *kasan_reset_tag(const void *addr);
> +static inline void *kasan_reset_tag(const void *addr)
> +{
> +       return (void *)arch_kasan_reset_tag(addr);

It seems that all implementations already return (void *), so the cast
is not needed.

> +}
>
>  bool kasan_report(unsigned long addr, size_t size,
>                 bool is_write, unsigned long ip);
> diff --git a/mm/kasan/hw_tags.c b/mm/kasan/hw_tags.c
> index b372421258c8..c3a0e83b5e7a 100644
> --- a/mm/kasan/hw_tags.c
> +++ b/mm/kasan/hw_tags.c
> @@ -24,11 +24,6 @@ void __init kasan_init_tags(void)
>         pr_info("KernelAddressSanitizer initialized\n");
>  }
>
> -void *kasan_reset_tag(const void *addr)
> -{
> -       return reset_tag(addr);
> -}
> -
>  void kasan_poison_memory(const void *address, size_t size, u8 value)
>  {
>         set_mem_tag_range(reset_tag(address),
> diff --git a/mm/kasan/kasan.h b/mm/kasan/kasan.h
> index 456b264e5124..0ccbb3c4c519 100644
> --- a/mm/kasan/kasan.h
> +++ b/mm/kasan/kasan.h
> @@ -246,15 +246,13 @@ static inline const void *arch_kasan_set_tag(const void *addr, u8 tag)
>         return addr;
>  }
>  #endif
> -#ifndef arch_kasan_reset_tag
> -#define arch_kasan_reset_tag(addr)     ((void *)(addr))
> -#endif
>  #ifndef arch_kasan_get_tag
>  #define arch_kasan_get_tag(addr)       0
>  #endif
>
> +/* kasan_reset_tag() defined in include/linux/kasan.h. */
> +#define reset_tag(addr)                ((void *)kasan_reset_tag(addr))

The cast is not needed.

I would also now remove reset_tag entirely by replacing it with
kasan_reset_tag. Having 2 names for the same thing does not add
clarity.


>  #define set_tag(addr, tag)     ((void *)arch_kasan_set_tag((addr), (tag)))
> -#define reset_tag(addr)                ((void *)arch_kasan_reset_tag(addr))
>  #define get_tag(addr)          arch_kasan_get_tag(addr)
>
>  #ifndef arch_init_tags
> diff --git a/mm/kasan/sw_tags.c b/mm/kasan/sw_tags.c
> index 099af6dc8f7e..4db41f274702 100644
> --- a/mm/kasan/sw_tags.c
> +++ b/mm/kasan/sw_tags.c
> @@ -67,11 +67,6 @@ u8 random_tag(void)
>         return (u8)(state % (KASAN_TAG_MAX + 1));
>  }
>
> -void *kasan_reset_tag(const void *addr)
> -{
> -       return reset_tag(addr);
> -}
> -
>  bool check_memory_region(unsigned long addr, size_t size, bool write,
>                                 unsigned long ret_ip)
>  {
> --
> 2.29.0.rc1.297.gfa9743e501-goog
>