From: "David Hildenbrand (Arm)" <david@kernel.org>
To: Kyle Zeng <kylebot@openai.com>, linux-mm@kvack.org
Cc: Andrew Morton <akpm@linux-foundation.org>,
Lorenzo Stoakes <ljs@kernel.org>, Rik van Riel <riel@surriel.com>,
"Liam R. Howlett" <liam@infradead.org>,
Vlastimil Babka <vbabka@kernel.org>, Harry Yoo <harry@kernel.org>,
Jann Horn <jannh@google.com>, Lance Yang <lance.yang@linux.dev>,
linux-kernel@vger.kernel.org, stable@vger.kernel.org
Subject: Re: [PATCH] mm/page_vma_mapped: continue past nonmatching huge PMDs
Date: Fri, 16 Oct 2026 09:46:13 +0200 [thread overview]
Message-ID: <1d850e66-2c8b-4912-829c-ab620de833e5@kernel.org> (raw)
In-Reply-To: <20261016011549.61146-1-kylebot@openai.com>
On 10/16/26 03:15, Kyle Zeng wrote:
> A PTE-mapped large folio can straddle PMD boundaries after an unaligned
> mremap(). If the first part is discarded and replaced with an unrelated
> huge PMD, page_vma_mapped_walk() stops instead of looking for the rest
> of the folio in subsequent PMDs.
>
> This also affects migration entries. A walk that stops at an unrelated
> huge PMD can leave migration PTEs behind when migration or an anonymous
> folio split restores the mappings. Those entries do not hold mapping
> references and can outlive the source folio.
> > Skip the current PMD rather than ending the walk on a flag or PFN
> mismatch. Do the same if the PMD became nonpresent before the locked
> recheck. Release the PMD lock, clear the per-PMD state and advance with
> step_forward(), so the existing range limit controls termination.
> This covers present, migration and device-private huge PMDs while
> preserving the matching-PMD and split-to-PTE paths.
>
> Fixes: ace71a19cec5 ("mm: introduce page_vma_mapped_walk()")
THP migration was added in
616b8371539 ("mm: thp: enable thp migration in generic path")
which was a couple (3?) of release after ace71a19cec5. Doesn't really make a
difference for backporting, so we can just keep the Fixes as is (it's the
obvious right thing to do :) ).
> Cc: <stable@vger.kernel.org>
> Assisted-by: LLM
We can drop these now.
> Signed-off-by: Kyle Zeng <kylebot@openai.com>
> ---
Thanks!
Acked-by: David Hildenbrand (Arm) <david@kernel.org>
--
Cheers,
David
prev parent reply other threads:[~2026-10-16 7:46 UTC|newest]
Thread overview: 4+ messages / expand[flat|nested] mbox.gz Atom feed top
2026-10-16 1:15 [PATCH] mm/page_vma_mapped: continue past nonmatching huge PMDs Kyle Zeng
2026-10-16 2:20 ` Andrew Morton
2026-10-16 2:56 ` Kyle Zeng
2026-10-16 7:46 ` David Hildenbrand (Arm) [this message]
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