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Wed, 09 Sep 2026 19:20:50 +0800 (CST) From: Hui Su To: "David Hildenbrand (Arm)" Cc: Matthew Brost , Andrew Morton , Balbir Singh , Zhi Wang , Joshua Hahn , Rakie Kim , Byungchul Park , Gourry , Ying Huang , Alex Popple , linux-mm@kvack.org, linux-kernel@vger.kernel.org, stable@vger.kernel.org Subject: Re: [PATCH v2] mm/migrate_device: avoid out-of-bounds writes for compound folios Date: Wed, 9 Sep 2026 20:20:49 +0900 Message-ID: <20260909112049.3202956-1-sh_def@163.com> X-Mailer: git-send-email 2.55.0 In-Reply-To: <5ae7a11c-1db4-44cd-bf67-a98cfd5ca08b@kernel.org> References: <20260817120758.669807-3-sh_def@163.com> <4ead5df7-f000-4087-83e4-13aae036e0b7@kernel.org> <5ae7a11c-1db4-44cd-bf67-a98cfd5ca08b@kernel.org> MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-CM-TRANSID:QCgvCgCnESERQaFqJi3hQg--.17578S2 X-Coremail-Antispam: 1Uf129KBjvJXoW7CrWUGF1kWryUCrWDKF18AFb_yoW8Gw4Dpa 4SgrZIyFsxWFWYkFnF9F48Xw1rWrsxJa4Yq3Z5Gr90ka1rJryFya40g3yDur17W3yIvrW8 X3y2q34UCF15Aa7anT9S1TB71UUUUU7qnTZGkaVYY2UrUUUUjbIjqfuFe4nvWSU5nxnvy2 9KBjDUYxBIdaVFxhVjvjDU0xZFpf9x07U5KsbUUUUU= X-CM-SenderInfo: xvkbvvri6rljoofrz/xtbC6hJXtmqhQRJoxwAA3u X-Rspam-User: X-Rspamd-Server: rspam08 X-Rspamd-Queue-Id: 09F5510000C X-Stat-Signature: fax5kmo8mow5hwa677kgraj69qqiqw8c X-HE-Tag: 1788952872-448300 X-HE-Meta: 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 FY6nJROc IAdHF3dAZROAbjFC16Itz2hnQLF5p6+22NqlaJNzO3cQPUFVdZKm5tyR9s1zkUkiosQvd1cLQeBtG6U/QmXBvXodi2aAqMRGpJ12pq/Yhs+May61waPcWAcBODx6llhgWHoZWHINzCCtETepP5eEm1/jb2XEB4Y85AC9AGrkZ+TzkHPpPU1hmUeAojO6F2wNKynfQQcHCO59LHsfm3eTBckz9aqZKIiKYguLr7qzhMVx20hk2SCrhdRitF6R4cD5z6GV9weUEcczg+c7YymzjYKHmPCnEyEpDAe85trs2cVky4tmYS9Z8iuHMK4a9kCj2Ex42lOaZ2SP7+fWW08Q4D8BogaEpPQii7FrZdH8vh+BiTXw7mKSb7SoJ4cOQ3kvudS84HuWywmB65j2KuzZEwzHJOWKH/E3Psqc+ Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On Mon, Sep 07, 2026 at 02:23:33PM +0200, David Hildenbrand (Arm) wrote: > That's what I was thinking: because how should we partially migrate folios? > Doesn't make sense :) > > If this cannot be triggered today, neither Fixes: nor CC: stable is appropriate. > > Agreed that we should just warn. Hi David, Matthew, Sorry, I missed this earlier. This fix has already landed in mainline, but I agree that the API semantics should be clarified. Partially migrating a compound folio does not make sense. If the intended contract is that callers must not provide a range that cuts through a compound folio, then treating such input as caller misuse with an explicit WARN/error path sounds reasonable. The reason I added the Fixes tag and Cc'd stable was that I observed an actual KASAN out-of-bounds write with the HMM migrate_anon_huge_zero selftest. The path was: dmirror_fops_release() -> dmirror_device_evict_chunk() -> migrate_device_range() My intent was to prevent migrate_device_range() from writing past the caller-provided src_pfns array when such an input is observed. That said, silently stopping the collection is not necessarily the best API semantics if this should be treated as caller misuse. I will rerun the reproducer on current mainline and report back with the result. If the preferred direction is to make this an explicit WARN/error path instead, I can send a follow-up patch on top of mainline. Thanks, Hui