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charset=UTF-8 Date: Tue, 07 Jul 2026 16:41:25 -0400 Message-Id: Cc: "sashiko-bot" To: "Usama Arif" , "Andrew Morton" , , , , , , , , , , , , , , , , , , , , , , From: "Zi Yan" Subject: Re: [PATCH 2/3] mm/madvise: skip device-private PMDs in cold and pageout walks X-Mailer: aerc 0.21.0 References: <20260707135255.292870-1-usama.arif@linux.dev> <20260707135255.292870-3-usama.arif@linux.dev> In-Reply-To: <20260707135255.292870-3-usama.arif@linux.dev> X-ClientProxiedBy: YQBPR0101CA0348.CANPRD01.PROD.OUTLOOK.COM (2603:10b6:c01:6b::25) To IA0PR12MB8374.namprd12.prod.outlook.com (2603:10b6:208:40e::7) Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 X-MS-PublicTrafficType: Email X-MS-TrafficTypeDiagnostic: IA0PR12MB8374:EE_|MN2PR12MB4471:EE_ X-MS-Office365-Filtering-Correlation-Id: e6a07c7f-2843-4c19-7821-08dedc6833fc X-MS-Exchange-SenderADCheck: 1 X-MS-Exchange-AntiSpam-Relay: 0 X-Microsoft-Antispam: BCL:0;ARA:13230040|1800799024|23010399003|7416014|376014|366016|4143699003|6133799003|22082099003|18002099003|11063799006|56012099006|921020; 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The subsequent > !pmd_present() branch has a VM_BUG_ON() asserting migration is the only > allowed non-present case; a device-private PMD trips it. > > Potential trigger: an HMM-based GPU driver races with > madvise(MADV_COLD)/MADV_PAGEOUT: pmd_trans_huge(*pmd) reads true, then > migrate_vma_pages() flips the PMD to a device-private entry before the > PMD lock is acquired. > > Skip device-private PMDs after taking the lock, before the !pmd_present() > check. > > Reported-by: sashiko-bot > Link: https://sashiko.dev/#/patchset/20260703173903.3789516-1-usama.arif%= 40linux.dev?part=3D6 > Fixes: 368076f52ebe ("mm/huge_memory: add device-private THP support to P= MD operations") > Signed-off-by: Usama Arif > --- > mm/madvise.c | 3 +++ > 1 file changed, 3 insertions(+) > LGTM. Reviewed-by: Zi Yan Since it could trigger VM_BUG_ON(), probably cc stable? --=20 Best Regards, Yan, Zi