Re: [PATCH v4 14/35] kmsan: Do not round up pg_data_t size

[Alexander Potapenko]

On Thu, Jun 13, 2024 at 5:39 PM Ilya Leoshkevich <iii@xxxxxxxxxxxxx> wrote:
>
> x86's alloc_node_data() rounds up node data size to PAGE_SIZE. It's not
> explained why it's needed, but it's most likely for performance
> reasons, since the padding bytes are not used anywhere. Some other
> architectures do it as well, e.g., mips rounds it up to the cache line
> size.
>
> kmsan_init_shadow() initializes metadata for each node data and assumes
> the x86 rounding, which does not match other architectures. This may
> cause the range end to overshoot the end of available memory, in turn
> causing virt_to_page_or_null() in kmsan_init_alloc_meta_for_range() to
> return NULL, which leads to kernel panic shortly after.
>
> Since the padding bytes are not used, drop the rounding.

Nice catch, thanks!

> Signed-off-by: Ilya Leoshkevich <iii@xxxxxxxxxxxxx>
Reviewed-by: Alexander Potapenko <glider@xxxxxxxxxx>