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

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Message-Id: <20250617163458.a414a62e49f029a41710c7ae@linux-foundation.org>
Date: Tue, 17 Jun 2025 16:34:58 -0700
From: Andrew Morton <akpm@...ux-foundation.org>
To: David Hildenbrand <david@...hat.com>
Cc: linux-kernel@...r.kernel.org, linux-fsdevel@...r.kernel.org, Muhammad
 Usama Anjum <usama.anjum@...labora.com>
Subject: Re: [PATCH v1] fs/proc/task_mmu: fix PAGE_IS_PFNZERO detection for
 the huge zero folio

On Tue, 17 Jun 2025 16:35:32 +0200 David Hildenbrand <david@...hat.com> 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@...ux-foundation.org>
> Cc: Muhammad Usama Anjum <usama.anjum@...labora.com>
> Signed-off-by: David Hildenbrand <david@...hat.com>
> ---
> 
> 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.