Re: [PATCH v1] fs/proc/task_mmu: fix PAGE_IS_PFNZERO detection for the huge zero folio

[David Hildenbrand]

On 18.06.25 01:34, Andrew Morton wrote:
> On Tue, 17 Jun 2025 16:35:32 +0200 David Hildenbrand <david@xxxxxxxxxx> wrote:
>
> > is_zero_pfn() does not work for the huge zero folio. Fix it by using
> > is_huge_zero_pmd().
> >
> > Found by code inspection.
> >
> > Fixes: 52526ca7fdb9 ("fs/proc/task_mmu: implement IOCTL to get and optionally clear info about PTEs")
> > Cc: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
> > Cc: Muhammad Usama Anjum <usama.anjum@xxxxxxxxxxxxx>
> > Signed-off-by: David Hildenbrand <david@xxxxxxxxxx>
> > ---
> >
> > Probably we should Cc stable, thoughts?
>
> Depends on the userspace effects.  I'm thinking these are "This can
> cause the PAGEMAP_SCAN ioctl against /proc/pid/pagemap to omit pages"
> so yup, cc:stable.

I think it will be included as PAGE_IS_PRESENT, but not as 
PAGE_IS_PFNZERO. That makes it a bit harder to judge the impact.

In any case, it's a simple patch and backporting should not really be 
hard (automatic).

--
Cheers,

David / dhildenb