From: Andrew Morton <akpm@linux-foundation.org>
To: Donggeun Yoo <donggeunyoo.kernel@gmail.com>
Cc: rppt@kernel.org, peterx@redhat.com, surenb@google.com,
aarcange@redhat.com, david@kernel.org, ljs@kernel.org,
liam@infradead.org, vbabka@kernel.org, mhocko@suse.com,
shuah@kernel.org, kirill@shutemov.name, linux-mm@kvack.org,
linux-kselftest@vger.kernel.org, linux-kernel@vger.kernel.org,
stable@vger.kernel.org
Subject: Re: [PATCH v2 1/2] userfaultfd: clear the inherited uffd bit in move_swap_pte()
Date: Thu, 24 Sep 2026 21:48:11 -0700 [thread overview]
Message-ID: <20260924214811.19ef8af417d37071ed8338c4@linux-foundation.org> (raw)
In-Reply-To: <20260925042907.2330519-2-donggeunyoo.kernel@gmail.com>
On Fri, 25 Sep 2026 13:29:06 +0900 Donggeun Yoo <donggeunyoo.kernel@gmail.com> wrote:
> UFFDIO_MOVE on a swapped-out page installs the source PTE at the
> destination unchanged, so a uffd bit set on the source lands in a
> destination VMA that was never registered for write protection. It
> can't be unset there, and THP collapse can't happen either, because a
> swap entry with the uffd bit set makes the scan bail.
>
> I don't think it's intentional because for an unswapped page the bit
> doesn't come along, and I don't see why being swapped out should change
> that.
>
> Clear the uffd bit on the moved swap entry unless the destination is
> RWP-registered.
Thanks, but...
When fixing a bug, please always fully describe the userspace-visible
effects of that bug.
> Fixes: adef440691ba ("userfaultfd: UFFDIO_MOVE uABI")
> Cc: <stable@vger.kernel.org>
Especially when proposing a backport.
Please review the first half-page of
Documentation/process/stable-kernel-rules.rst
I don't mean "be reluctant to backport". I mean "when proposing a
backport, explain *why*".
> Assisted-by: LLM
Great! Please add a prompt to LLM's .md ensuring that future
changelogs always provide this information. Please also share that
update with the rest of your organization.
next prev parent reply other threads:[~2026-09-25 4:48 UTC|newest]
Thread overview: 6+ messages / expand[flat|nested] mbox.gz Atom feed top
2026-09-25 4:29 [PATCH v2 0/2] " Donggeun Yoo
2026-09-25 4:29 ` [PATCH v2 1/2] " Donggeun Yoo
2026-09-25 4:48 ` Andrew Morton [this message]
2026-09-25 7:36 ` David Hildenbrand (Arm)
2026-09-25 4:29 ` [PATCH v2 2/2] selftests/mm: add a test for UFFDIO_MOVE of a write-protected swap entry Donggeun Yoo
2026-09-25 7:41 ` David Hildenbrand (Arm)
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