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b=O4IFuFM1wBnG5IoIRjgNYn5M8R yzQ17YZVu+DTTQqp2TG3tqXwJHa9zOWkzLPh3kiTbeewYVLkWcaLQD9CuP5awSpvhywIBxQI6I5hK OdiA4fEHX49T8jROdHejMOhNVLnmwqP9X4nLNK8CySsZ2TpYW2y99Q5UOp+SjmO/4gisRzsg6yJj4 iAj50RyXvwHGwsB8JB8fIDq4HikVtu1//Hp9OwYv6DgUuLMsg/a1RuHzprfnwqJmCD2Mu012rT0IV JM7wFdfSrm1shFJgBTyXp9vHlxU0S0/rx69AwQ6wflsxB6LXcgUIaF11MQL1sCqqd7f11/ad6TbHe 2SktyLhw==; Received: from fangorn.home.surriel.com ([10.0.13.7]) by shelob.surriel.com with esmtpsa (TLS1.2) tls TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384 (Exim 4.97.1) (envelope-from ) id 1wgSD3-000000004CM-0Hzy; Sun, 05 Jul 2026 15:08:57 -0400 Message-ID: <06bc706b4f7ed59950915c6c5f6e9752b6e85216.camel@surriel.com> Subject: Re: [PATCH] userfaultfd: wait on source PMD during UFFDIO_MOVE From: Rik van Riel To: Usama Arif , Andrew Morton , baohua@kernel.org, baolin.wang@linux.alibaba.com, david@kernel.org, dev.jain@arm.com, lance.yang@linux.dev, liam@infradead.org, linux-kernel@vger.kernel.org, linux-mm@kvack.org, ljs@kernel.org, npache@redhat.com, ryan.roberts@arm.com, ziy@nvidia.com, aarcange@redhat.com, shakeel.butt@linux.dev, hannes@cmpxchg.org, kernel-team@meta.com Cc: sashiko-bot Date: Sun, 05 Jul 2026 15:08:56 -0400 In-Reply-To: <20260705131231.1499198-1-usama.arif@linux.dev> References: <20260705131231.1499198-1-usama.arif@linux.dev> Autocrypt: addr=riel@surriel.com; 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charset="UTF-8" Content-Transfer-Encoding: quoted-printable User-Agent: Evolution 3.56.2 (3.56.2-2.fc42) Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 On Sun, 2026-07-05 at 06:12 -0700, Usama Arif wrote: > move_pages_huge_pmd() snapshots src_pmdval under src_ptl, drops the > lock, > and, for migration entries, waits with pmd_migration_entry_wait(). >=20 > Passing &src_pmdval is wrong. pmd_migration_entry_wait() must lock > and > re-read the real page-table PMD; on split-PMD-lock kernels, a stack > address also resolves to the wrong lock. > softleaf_entry_wait_on_locked() > then waits without a folio reference, which is safe only while > serialized > against migration-entry removal by the real PT lock. >=20 > Pass src_pmd, matching __handle_mm_fault() and hmm_vma_walk_pmd(). >=20 > Reported-by: sashiko-bot > Link: > https://sashiko.dev/#/patchset/20260703173903.3789516-1-usama.arif%40linu= x.dev?part=3D8 > Fixes: adef440691ba ("userfaultfd: UFFDIO_MOVE uABI") > Signed-off-by: Usama Arif Reviewed-by: Rik van Riel --=20 All Rights Reversed.