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dkim=none (message not signed) header.d=none;dmarc=none action=none header.from=nvidia.com; Received: from IA0PR12MB8374.namprd12.prod.outlook.com (2603:10b6:208:40e::7) by PH0PR12MB7470.namprd12.prod.outlook.com (2603:10b6:510:1e9::20) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id 15.21.615.10; Thu, 12 Nov 2026 15:44:35 +0000 Received: from IA0PR12MB8374.namprd12.prod.outlook.com ([fe80::d85f:4c87:ae84:3f16]) by IA0PR12MB8374.namprd12.prod.outlook.com ([fe80::d85f:4c87:ae84:3f16%6]) with mapi id 15.21.0615.007; Thu, 12 Nov 2026 15:44:35 +0000 From: Zi Yan To: Usama Arif Cc: Andrew Morton , apopple@nvidia.com, byungchul@sk.com, david@kernel.org, gourry@gourry.net, jannh@google.com, joshua.hahnjy@gmail.com, liam@infradead.org, linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org, linux-mm@kvack.org, ljs@kernel.org, matthew.brost@intel.com, mhocko@suse.com, pfalcato@suse.de, rppt@kernel.org, surenb@google.com, vbabka@kernel.org, ying.huang@linux.alibaba.com, kas@kernel.org, hannes@cmpxchg.org, riel@surriel.com, shakeel.butt@linux.dev, kernel-team@meta.com, baolin.wang@linux.alibaba.com, Nico Pache , ryan.roberts@arm.com, dev.jain@arm.com, baohua@kernel.org, lance.yang@linux.dev, stable@vger.kernel.org Subject: Re: [PATCH 2/3] fs/proc/task_mmu: don't read young/dirty from a non-present PMD in smaps Date: Thu, 12 Nov 2026 10:44:31 -0500 X-Mailer: MailMate (3.0r7038) Message-ID: <7A78EF9B-1D4A-407A-9948-7AF4DBDDB732@nvidia.com> In-Reply-To: <20261111113904.650722-3-usama.arif@linux.dev> References: <20261111113904.650722-1-usama.arif@linux.dev> <20261111113904.650722-3-usama.arif@linux.dev> Content-Type: text/plain X-MS-Reactions: disallow X-ClientProxiedBy: YT4P288CA0085.CANP288.PROD.OUTLOOK.COM (2603:10b6:b01:d0::16) To IA0PR12MB8374.namprd12.prod.outlook.com (2603:10b6:208:40e::7) X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Post: List-Help: List-Subscribe: List-Unsubscribe: List-Owner: Precedence: list MIME-Version: 1.0 X-MS-PublicTrafficType: Email X-MS-TrafficTypeDiagnostic: IA0PR12MB8374:EE_|PH0PR12MB7470:EE_ X-MS-Office365-Filtering-Correlation-Id: 6452bca4-f030-4926-ff1f-08df40d3da03 X-MS-Exchange-SenderADCheck: 1 X-MS-Exchange-AntiSpam-Relay: 0 X-Microsoft-Antispam: BCL:0;ARA:13230040|23010399003|1800799024|376014|7416014|366016|18002099003|22082099003|4143699003|11063799006|56012099006|10067099003|261102123227099003|261021123027099003|261021121427099003; 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X-MS-Exchange-AntiSpam-MessageData-ChunkCount: 1 X-MS-Exchange-AntiSpam-MessageData-0: =?us-ascii?Q?hIuE31khTkbCLWouxHi9o5PvDnESdvlhbfpfjH5fj95dGDCquSIARrWBsnnF?= =?us-ascii?Q?VX/DZ/KKVKtDxed9y28CKdWVE8+sBU/txIBxusgGYoHLy0op9DP8npqLILWk?= =?us-ascii?Q?6YnvuoQ3uAeSEcNnJwHYgy+bXD8bZOxRA6PIjxi8lIFptBvFptevVsFBPYxc?= =?us-ascii?Q?Rf1+Ph9S2eiD7RQpVn4eoCTEwYblw1MrwVTs7L9JTjQF+PP3jKtL/KSQzQXI?= =?us-ascii?Q?kKgM+a23GJUuWTX2BEvc9ri4lF8BP1CpwnEkpiuQShBIGK6VD7TPoVOTSUBV?= =?us-ascii?Q?uEBB3KNWr8mOFFdvVuXw1WXqqZ4TUDUSxaARb4dEuxfh8ruyHFE/CwwZDVEx?= =?us-ascii?Q?wrRUWE+PANi6zvqRHTJJNf2FnLczxscHFXGXg+4rC2dEiR+yEihur5lBrzvw?= =?us-ascii?Q?/+MV1RVD8co+RsBi7kfUoegJAjuMfuCue90Ws65un/1ul3ZUlgrAVJgzqNXZ?= =?us-ascii?Q?qnsaZ68bEq1o9+3pJbrexxGq405hjD/bSqQsrtAakuuRGBsdt2NVyh0UZlR3?= =?us-ascii?Q?8PqUX2rrp+j9lzsSxfeQbUrP+aIi4LyQQjLVFL7c5+FzqlI8VCK/tB7jJW+o?= =?us-ascii?Q?Cd+dIYhTt/FtDiRxqyHbyIF25zMF7G8wRjIE2C/dubZfFxspcb00zN5dP63m?= =?us-ascii?Q?bHdIFJj9tYO/sIgATg+qe+U+As/e/jwMKzdBkBeaHV24/XRFnug3DRw4JORs?= =?us-ascii?Q?urO0yXFhn3iG1D3ONnB84s8+dP0urwQxhtVi3zax7t535PwMDO+3kXMUKQpv?= =?us-ascii?Q?XWL+2qQSz+k0fpuzsLe0TcKR11YU5EJXHzGlPGE/Kf5zP1aXWS353CyKiDeB?= =?us-ascii?Q?JhvXsad6Em57AQLxsVrI79lqZWISYSTghb0Yei8QZWt+oHT2evIvVXn2DePA?= =?us-ascii?Q?J85+en5DVvrNchN8uikavLugJfUz54kUhUTdE/w0Brwy7W+CubkV08D9fk+i?= =?us-ascii?Q?ZzhwlGO8HZd9NNdggAgwgBzPyjwmCiWAwHffVyvGcEpQWugcPll0uhjACIXF?= =?us-ascii?Q?61Q07uM2XYt/h6zxhayUq9ZfTEvpauDtPkjXOxd8rp1mQ3bJy26VIaRa5hMf?= =?us-ascii?Q?R9uc0V5Jc5Ww9mDkYKc0oNzmXdY3fviqjOG4cv8O1hGXC28leL2Pjr/ICkle?= =?us-ascii?Q?7DUxXBizbohnodVe1icMl/ngQAIudVezGhdFhv4GV3XDSS9Htjy/ZsOeTzZF?= =?us-ascii?Q?phFRO9W/qPKYjjtdz08B/LOQpFnTBtfJg3Q8s8GsowzyUGWOc+1xQE0rps+9?= =?us-ascii?Q?bZAS1+Xtohmxb7LUc8mLkA42v6lb176KmIfaa7A0r3b86PRoOkynP3/3O2+d?= =?us-ascii?Q?HUZ7MMbbgGcm0uRP9WvF/RMpqfoFb6wYAL1qJWQD9yJ4zkgMWXvKEDI7kX76?= =?us-ascii?Q?LOUT0CmNE8685de7Bi6ujBAvJ6rfVX/tQkF+UftO6iA5ei80EHeA9e5xjsWF?= =?us-ascii?Q?IJSXdgVJP8+/A//Tl9tSQdPvkxmq3fPaLTHAohNT1jgvO5fvcSDpNnT4XaNg?= =?us-ascii?Q?tRJEnntCBGosQvaYw+Xl8SMnJcB/4TdkIVsljhIgYZfl33mMmxi09cDAM7Ye?= =?us-ascii?Q?rxYZSFj7XdJYZNDChgfoUm4mweu3c1ISyr2VbpsWVqb7wpBX7szt5Ajv3bi0?= =?us-ascii?Q?0CcfbQV+vO4+949SxuOpFmJBHUOkLB5gmuxflKC4CTaR9mmGjppcsxCYT4l4?= =?us-ascii?Q?6jHBOXbVv4srLq4WKIa//WSa6gyfgr7iUkGp4hITnJMHfAGh?= X-OriginatorOrg: Nvidia.com X-MS-Exchange-CrossTenant-Network-Message-Id: 6452bca4-f030-4926-ff1f-08df40d3da03 X-MS-Exchange-CrossTenant-AuthSource: IA0PR12MB8374.namprd12.prod.outlook.com X-MS-Exchange-CrossTenant-AuthAs: Internal X-MS-Exchange-CrossTenant-OriginalArrivalTime: 12 Nov 2026 15:44:35.1551 (UTC) X-MS-Exchange-CrossTenant-FromEntityHeader: Hosted X-MS-Exchange-CrossTenant-Id: 43083d15-7273-40c1-b7db-39efd9ccc17a X-MS-Exchange-CrossTenant-MailboxType: HOSTED X-MS-Exchange-CrossTenant-UserPrincipalName: eEiO96KhMn3dJ6JefROsDGws07brrwvWZ9g5p/vOjqselb25nR0dhrRhZ2pX4iMu X-MS-Exchange-Transport-CrossTenantHeadersStamped: PH0PR12MB7470 On 11 Nov 2026, at 6:38, Usama Arif wrote: > smaps_pmd_entry() passes pmd_young(*pmd) and pmd_dirty(*pmd) to > smaps_account() for every PMD, including migration and device-private > entries, where those bits hold part of the swap offset rather than > accessed/dirty state. smaps_pte_entry() only reads them when the entry > is present. > > On x86_64 the offset is stored inverted across bits 9-58, which overlap > _PAGE_SAVED_DIRTY, so pmd_dirty() returns garbage: a clean 2MB > device-private mapping is accounted as 2048 kB dirty, and lazyfree > accounting is suppressed. pgtable_64.h also warns that the hardware can > set the accessed and dirty bits on non-present entries by mistake. > > Only read the bits when the PMD is present. > > Fixes: c94b6923fa0a ("/proc/PID/smaps: Add PMD migration entry parsing") > Cc: stable@vger.kernel.org > Signed-off-by: Usama Arif > --- > fs/proc/task_mmu.c | 7 ++++--- > 1 file changed, 4 insertions(+), 3 deletions(-) > Makes sense. Reviewed-by: Zi Yan Best Regards, Yan, Zi