Re: [PATCH v9 10/44] kasan: define KASAN_GRANULE_PAGE

[Alexander Potapenko]

On Tue, Nov 10, 2020 at 11:11 PM Andrey Konovalov <andreyknvl@xxxxxxxxxx> wrote:
>
> Define KASAN_GRANULE_PAGE as (KASAN_GRANULE_SIZE << PAGE_SHIFT), which is
> the same as (KASAN_GRANULE_SIZE * PAGE_SIZE), and use it across KASAN code
> to simplify it.

What's the physical sense behind KASAN_GRANULE_PAGE? Is it something
more than just a product of two constants?
The name suggests it might be something page-sized, but in reality it is not.

>
> Signed-off-by: Andrey Konovalov <andreyknvl@xxxxxxxxxx>
> Signed-off-by: Vincenzo Frascino <vincenzo.frascino@xxxxxxx>
> Reviewed-by: Marco Elver <elver@xxxxxxxxxx>
> ---
> Change-Id: I0b627b24187d06c8b9bb2f1d04d94b3d06945e73
> ---
>  mm/kasan/init.c   | 10 ++++------
>  mm/kasan/kasan.h  |  1 +
>  mm/kasan/shadow.c | 16 +++++++---------
>  3 files changed, 12 insertions(+), 15 deletions(-)
>
> diff --git a/mm/kasan/init.c b/mm/kasan/init.c
> index 1a71eaa8c5f9..26b2663b3a42 100644
> --- a/mm/kasan/init.c
> +++ b/mm/kasan/init.c
> @@ -441,9 +441,8 @@ void kasan_remove_zero_shadow(void *start, unsigned long size)
>         addr = (unsigned long)kasan_mem_to_shadow(start);
>         end = addr + (size >> KASAN_SHADOW_SCALE_SHIFT);
>
> -       if (WARN_ON((unsigned long)start %
> -                       (KASAN_GRANULE_SIZE * PAGE_SIZE)) ||
> -           WARN_ON(size % (KASAN_GRANULE_SIZE * PAGE_SIZE)))
> +       if (WARN_ON((unsigned long)start % KASAN_GRANULE_PAGE) ||
> +           WARN_ON(size % KASAN_GRANULE_PAGE))
>                 return;
>
>         for (; addr < end; addr = next) {
> @@ -476,9 +475,8 @@ int kasan_add_zero_shadow(void *start, unsigned long size)
>         shadow_start = kasan_mem_to_shadow(start);
>         shadow_end = shadow_start + (size >> KASAN_SHADOW_SCALE_SHIFT);
>
> -       if (WARN_ON((unsigned long)start %
> -                       (KASAN_GRANULE_SIZE * PAGE_SIZE)) ||
> -           WARN_ON(size % (KASAN_GRANULE_SIZE * PAGE_SIZE)))
> +       if (WARN_ON((unsigned long)start % KASAN_GRANULE_PAGE) ||
> +           WARN_ON(size % KASAN_GRANULE_PAGE))
>                 return -EINVAL;
>
>         ret = kasan_populate_early_shadow(shadow_start, shadow_end);
> diff --git a/mm/kasan/kasan.h b/mm/kasan/kasan.h
> index c31e2c739301..1865bb92d47a 100644
> --- a/mm/kasan/kasan.h
> +++ b/mm/kasan/kasan.h
> @@ -7,6 +7,7 @@
>
>  #define KASAN_GRANULE_SIZE     (1UL << KASAN_SHADOW_SCALE_SHIFT)
>  #define KASAN_GRANULE_MASK     (KASAN_GRANULE_SIZE - 1)
> +#define KASAN_GRANULE_PAGE     (KASAN_GRANULE_SIZE << PAGE_SHIFT)
>
>  #define KASAN_TAG_KERNEL       0xFF /* native kernel pointers tag */
>  #define KASAN_TAG_INVALID      0xFE /* inaccessible memory tag */
> diff --git a/mm/kasan/shadow.c b/mm/kasan/shadow.c
> index ca0cc4c31454..1fadd4930d54 100644
> --- a/mm/kasan/shadow.c
> +++ b/mm/kasan/shadow.c
> @@ -161,7 +161,7 @@ static int __meminit kasan_mem_notifier(struct notifier_block *nb,
>         shadow_end = shadow_start + shadow_size;
>
>         if (WARN_ON(mem_data->nr_pages % KASAN_GRANULE_SIZE) ||
> -               WARN_ON(start_kaddr % (KASAN_GRANULE_SIZE << PAGE_SHIFT)))
> +               WARN_ON(start_kaddr % KASAN_GRANULE_PAGE))
>                 return NOTIFY_BAD;
>
>         switch (action) {
> @@ -432,22 +432,20 @@ void kasan_release_vmalloc(unsigned long start, unsigned long end,
>         unsigned long region_start, region_end;
>         unsigned long size;
>
> -       region_start = ALIGN(start, PAGE_SIZE * KASAN_GRANULE_SIZE);
> -       region_end = ALIGN_DOWN(end, PAGE_SIZE * KASAN_GRANULE_SIZE);
> +       region_start = ALIGN(start, KASAN_GRANULE_PAGE);
> +       region_end = ALIGN_DOWN(end, KASAN_GRANULE_PAGE);
>
> -       free_region_start = ALIGN(free_region_start,
> -                                 PAGE_SIZE * KASAN_GRANULE_SIZE);
> +       free_region_start = ALIGN(free_region_start, KASAN_GRANULE_PAGE);
>
>         if (start != region_start &&
>             free_region_start < region_start)
> -               region_start -= PAGE_SIZE * KASAN_GRANULE_SIZE;
> +               region_start -= KASAN_GRANULE_PAGE;
>
> -       free_region_end = ALIGN_DOWN(free_region_end,
> -                                    PAGE_SIZE * KASAN_GRANULE_SIZE);
> +       free_region_end = ALIGN_DOWN(free_region_end, KASAN_GRANULE_PAGE);
>
>         if (end != region_end &&
>             free_region_end > region_end)
> -               region_end += PAGE_SIZE * KASAN_GRANULE_SIZE;
> +               region_end += KASAN_GRANULE_PAGE;
>
>         shadow_start = kasan_mem_to_shadow((void *)region_start);
>         shadow_end = kasan_mem_to_shadow((void *)region_end);
> --
> 2.29.2.222.g5d2a92d10f8-goog
>


-- 
Alexander Potapenko
Software Engineer

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