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Howlett" , Vlastimil Babka , Mike Rapoport , Suren Baghdasaryan , Michal Hocko , David Rientjes , Shakeel Butt , Andrew Morton , Jann Horn , Pedro Falcato , "Matthew Wilcox (Oracle)" , Jan Kara , Nhat Pham , Johannes Weiner , Zi Yan , Matthew Brost , Joshua Hahn , Byungchul Park , Gregory Price , Ying Huang , Alistair Popple , Usama Arif , Kairui Song , =?utf-8?B?SsOpcsO0bWU=?= Glisse , Kiryl Shutsemau , Yu-cheng Yu , Dave Hansen , Dennis Zhou , Tejun Heo , Christoph Lameter , Peng Fan , Josef Bacik , Chris Mason , linux-mm@kvack.org, linux-kernel@vger.kernel.org, linux-fsdevel@vger.kernel.org, "Borislav Petkov (AMD)" , Mark Brown , "Dennis Zhou (Facebook)" , Rick Edgecombe , stable@vger.kernel.org Subject: Re: [PATCH 08/13] mm/migrate_device: fix ksmd oops on a migrated KSM page Message-ID: References: <20261111-mason-migrate-et-al-fixes-v1-0-3d2454362e8d@kernel.org> <20261111-mason-migrate-et-al-fixes-v1-8-3d2454362e8d@kernel.org> Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20261111-mason-migrate-et-al-fixes-v1-8-3d2454362e8d@kernel.org> X-ClientProxiedBy: MEVP282CA0024.AUSP282.PROD.OUTLOOK.COM (2603:10c6:220:200::7) To CH3PR12MB9730.namprd12.prod.outlook.com (2603:10b6:610:253::9) 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: CH3PR12MB9730:EE_|SN7PR12MB6929:EE_ X-MS-Office365-Filtering-Correlation-Id: 0ce8285c-e060-47ee-4cd9-08df404b67d7 X-MS-Exchange-SenderADCheck: 1 X-MS-Exchange-AntiSpam-Relay: 0 X-Microsoft-Antispam: BCL:0;ARA:13230040|376014|23010399003|7416014|366016|1800799024|18002099003|22082099003|4143699003|11063799006|261026121527099003|261009223027099003|56012099006|261021121427099003|261102123227099003|10067099003; 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X-MS-Exchange-AntiSpam-MessageData-ChunkCount: 1 X-MS-Exchange-AntiSpam-MessageData-0: =?us-ascii?Q?fJmrZxY+7v2cKX4TowLnux3V8SsYeO5SuXMrlWLQZpNWn1x+wyRSN212xuNg?= =?us-ascii?Q?KXi1deJTK1o8nZDLkCC8dkpQULTU5t44jVQc2RnB7EjoX4LORMcG/wjJK8R3?= =?us-ascii?Q?ksQW+iMJroQK7m2EVY1jSOnYL8MEco8SmwS7SJ36bPWFJi/l7pL07Vs1uG6n?= =?us-ascii?Q?ZcH3dsebjD2N71a5mgJy3VDnMLdvRGicWDRuYv4Bwcf0Y9uqM18vTpw/HkvW?= =?us-ascii?Q?EzFEDATs76FdbrCi/Z+DLogKMpllg5w0FVlpY1T7qNQ8FEPt8SdF7/dufC7z?= =?us-ascii?Q?dw3bs94nyA86+TqTL3wemB09jTAvBlhABQt1i1FKWGSXG8kH7iePBgfVXzQ4?= =?us-ascii?Q?U1rm160yKCPyk89eJsUP/CglMXMJ0+ZLbWqAF2j49g78bRRWSyYeznK/Co1V?= =?us-ascii?Q?/a5TZMdA1QX3Si8O0D/fmDFB069zkDm1Y98p4iJh+RqHuqrzxZrXFtY+o/GF?= =?us-ascii?Q?oQLutlsP21ih/oBq2jtNnSfNAGFmNuIFGCgec8uu0kPtJ2109YP1wIJy36TU?= =?us-ascii?Q?LaHVh8o1xISiDYfSTMeO8xylzP+wNKXMgXi34CfmkGrbDucBD4NS3tlAcyTs?= =?us-ascii?Q?uqxErufU+qOSnRzs+J11eT58Gj4rLQ+fc2LCu4GXvQ+6BlPjPwlncrIgMUoI?= =?us-ascii?Q?JmsLuRJJsTqjXPJOCnCB6gAnA+5CwBqMjIDWI+5MiqzksqJ6ItT/glQkHfLj?= =?us-ascii?Q?ixuk0sVWXC4X+i0veynT7w8fRZr8mz3aHmGKnQ99Mfw/9/sKx3iR9+gLQfvT?= =?us-ascii?Q?24w7MdfJ5NEnoY4ALgsNF0+zaCN1qqSXe/AadWKiDRsVJ1XdgXHHBUuQgQhD?= =?us-ascii?Q?1jN++T7HVmkf1pacjucvtFG9Cql6D34TmOYH9u/D1VPZOWPmAJaCAi3pzQDJ?= =?us-ascii?Q?QK6J8n86y1tDXy4ZhUtD4ToRMEwyeRuxSoSLNzBmsnKYu/m3GgFI+5S2ar8I?= =?us-ascii?Q?kQ0JiV0NHajveA1cn0NvP7vwKSM4wVW1l3ShBs4hGLG3q1iT62DxXk/umM+y?= =?us-ascii?Q?B49o3ollUm1zpGgR3Dx16r3cDpDCGmZX8D5xkq7AHBMRl9LS0wgOKA7EF8g0?= =?us-ascii?Q?G1W/2lk70mW88JaNNa58qLxEyq4I6RuqShP+MwxXSG7qr1MLRQ0faa9DhTgs?= =?us-ascii?Q?XXBzISVgI4/md/ZghXaR3AdQ1cXgml7EmwtdS4wtunvv93HWqAPwnWy4wnp6?= =?us-ascii?Q?DKenP5hm6oruJYLD6p3FIvpKN5/kUFlECmlyY3FcVIZchibOaDHmOC5kx55J?= =?us-ascii?Q?kufA+2i9RgVB7wDZS5+QbyYhJO32wlqR0Kl8f2Pxa+L1FUBOOMm1WNhFcKXj?= =?us-ascii?Q?k9G+VNDyGtWcyS//5KC+1d+N/7MZV2UAdqTzL/hpfxVSDEcQJISyO5PB+ro+?= =?us-ascii?Q?XeXpdPyCbTHWnpVHS0HwKlryXYeX3nCj7jPwo/HhxAoR4FRuD9NGGLvsDpP7?= =?us-ascii?Q?LzyPKAZbq/BZGU/aOG6Py+P6p9og0TubSpuwdRITtb2FGx65ZXWAF8J5kmLa?= =?us-ascii?Q?5ireYXkssNRjqmzyQATqTYsIgdoYgdt3s0WKO4UAS09Tru6nARJ0yJEF/rvS?= =?us-ascii?Q?WHLhK2TkeGp0x2HRKE97iyjP869xEY5AThduqq0AUwmHEU3a26GRpD4exUYn?= =?us-ascii?Q?0Xmgp1ErRg1PCqmlOAMbTjh61j2puC52aUZixYTSzGVbPNQBIW4kUwIetlKj?= =?us-ascii?Q?9Nvhyi9bzTeJCAKKItSXDgjben2rOntWYa7d0jnEmWW9CVTQMaE7KTCuBU7a?= =?us-ascii?Q?KBUTDDyF4w=3D=3D?= X-OriginatorOrg: Nvidia.com X-MS-Exchange-CrossTenant-Network-Message-Id: 0ce8285c-e060-47ee-4cd9-08df404b67d7 X-MS-Exchange-CrossTenant-AuthSource: CH3PR12MB9730.namprd12.prod.outlook.com X-MS-Exchange-CrossTenant-AuthAs: Internal X-MS-Exchange-CrossTenant-OriginalArrivalTime: 11 Nov 2026 23:27:52.1773 (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: nHN9sGAvqYLtpFd6rSrn12I4PWSPdDzDc9E81VTIH5cGmj4WPUCaBzVty0s2CrlLR24NtgVuwQUn0wLcDLFnUw== X-MS-Exchange-Transport-CrossTenantHeadersStamped: SN7PR12MB6929 On Wed, Nov 11, 2026 at 06:13:22PM +0000, Lorenzo Stoakes (ARM) wrote: > From: Chris Mason > > After a KSM page is migrated to device private memory, ksmd can oops, > and KSM then stops until reboot. A process that maps the page can also > loop in page faults when it next accesses the page. > > The problem arises because KSM doesn't know not to try to look at device > private memory that does not exist in the direct map. > > Disallow this from happening by explicitly testing for this scenario in > __migrate_device_pages(). > > Fixes: a5430dda8a3a ("mm/migrate: support un-addressable ZONE_DEVICE page in migration") > Cc: > Signed-off-by: Chris Mason > [ ljs: tweak commit message, comment ] > Signed-off-by: Lorenzo Stoakes (ARM) > --- > mm/migrate_device.c | 9 +++++++++ > 1 file changed, 9 insertions(+) > > diff --git a/mm/migrate_device.c b/mm/migrate_device.c > index 45e571dbfb4c..7ebd02ec303b 100644 > --- a/mm/migrate_device.c > +++ b/mm/migrate_device.c > @@ -1205,6 +1205,15 @@ static void __migrate_device_pages(unsigned long *src_pfns, > } > > > + /* > + * KSM doesn't know not to try to read device private pages, so > + * disallow the combination. > + */ > + if (folio_is_device_private(newfolio) && folio_test_ksm(folio)) { > + src_pfns[i] &= ~MIGRATE_PFN_MIGRATE; > + goto next; > + } > + > if (folio_is_device_private(newfolio) || > folio_is_device_coherent(newfolio)) { > if (mapping) { > Given that we don't move device private ksm folios, I guess the check in pin_anon_rmap() now applies only to device coherent folios. I agree with the comment earlier about detecting this condition earlier. Acked-by: Balbir Singh