Re: [PATCH v2] mm/memblock: Correct totalram_pages accounting with KMSAN

[Mike Rapoport <rppt@kernel.org>]

On Wed, Sep 24, 2025 at 12:03:01PM +0200, Alexander Potapenko wrote:
> When KMSAN is enabled, `kmsan_memblock_free_pages()` can hold back pages
> for metadata instead of returning them to the early allocator. The callers,
> however, would unconditionally increment `totalram_pages`, assuming the
> pages were always freed. This resulted in an incorrect calculation of the
> total available RAM, causing the kernel to believe it had more memory than
> it actually did.
> 
> This patch refactors `memblock_free_pages()` to return the number of pages
> it successfully frees. If KMSAN stashes the pages, the function now
> returns 0; otherwise, it returns the number of pages in the block.
> 
> The callers in `memblock.c` have been updated to use this return value,
> ensuring that `totalram_pages` is incremented only by the number of pages
> actually returned to the allocator. This corrects the total RAM accounting
> when KMSAN is active.
> 
> Cc: Aleksandr Nogikh <nogikh@google.com>
> Fixes: 3c2065098260 ("init: kmsan: call KMSAN initialization routines")
> Signed-off-by: Alexander Potapenko <glider@google.com>
> Reviewed-by: David Hildenbrand <david@redhat.com>

Reviewed-by: Mike Rapoport (Microsoft) <rppt@kernel.org>

-- 
Sincerely yours,
Mike.