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    SubjectRe: [PATCH v9 10/44] kasan: define KASAN_GRANULE_PAGE
    On Tue, Nov 10, 2020 at 11:11 PM Andrey Konovalov <andreyknvl@google.com> 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@google.com>
    > Signed-off-by: Vincenzo Frascino <vincenzo.frascino@arm.com>
    > Reviewed-by: Marco Elver <elver@google.com>
    > ---
    > 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

    Google Germany GmbH
    Erika-Mann-Straße, 33
    80636 München

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