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b=mBbJ0AG85Go83iWFJVKJrU87L9CaAbCtMGm6NjiNKpqM7xtTKxKZvef54DAST8hdY +qge4H+e+pCaCp35Z1lQNebvY2P1qqK32vopKcRR0ex2koXo/Ox5iw650cODpaRjLs Dx4kTv+n0Xgy11j7vQIgkcBlXm0McLH6kDK8NYwc= Date: Thu, 24 Sep 2026 21:48:11 -0700 From: Andrew Morton To: Donggeun Yoo 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() Message-Id: <20260924214811.19ef8af417d37071ed8338c4@linux-foundation.org> In-Reply-To: <20260925042907.2330519-2-donggeunyoo.kernel@gmail.com> References: <20260925042907.2330519-1-donggeunyoo.kernel@gmail.com> <20260925042907.2330519-2-donggeunyoo.kernel@gmail.com> X-Mailer: Sylpheed 3.8.0beta1 (GTK+ 2.24.33; x86_64-pc-linux-gnu) Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit X-Rspam-User: X-Stat-Signature: nygu87yqbiy9rcko9bda399q3xntxi3d X-Rspamd-Server: rspam11 X-Rspamd-Queue-Id: 793341C0007 X-HE-Tag: 1790311693-472215 X-HE-Meta: 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 TJkyXSlR w0JXC/WgX1xUErFnXp3Pu4FscuQAz16RcWU+sjEIYuiMR/DWdC4XfHuITVcnM1Cf+d577ckaLjroLBgVKARaGPD7K4oLKCn7K2S7UIaFXKDqkOHtuK5MZDbh4PYWl3aJHQulWbX7WO2MPFW9piTZ9eJjXsUWk4DeAO6HLswN4nEXyCMTOkZm6oVsRHAZJHPQ0FbnTaGwJOFAr0IqKjJVKl+jKtjm5fi4K8H1S/D4240EDEMtmrUArrGNAMmocN8J8lcGHfyBB5YSrjG9Zp5cY8sinWUGbMPB3mBNPHZyR9AnS3FJlnXop9AWLJuHzndSSHz7Zk458Vqlo8iPeMTKZdBilNW/h+0DfXLxObbQDkA5w86NmkYM7cZNFbkMMxL9AMgNW+tnJQRsZ9WJp9cpWAuCm/dAfSD0KBT16 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On Fri, 25 Sep 2026 13:29:06 +0900 Donggeun Yoo 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: 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.