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X-MS-Exchange-AntiSpam-MessageData-ChunkCount: 1 X-MS-Exchange-AntiSpam-MessageData-0: =?us-ascii?Q?Y13EuX5oa8fXN9Ib7w0E6WAnpo8Hh09NSupTeL8Wqc3pNut3qet6HqJ3VTpW?= =?us-ascii?Q?tC6qW4mwFBUqrZA5hGOlGAVgQ1vIWrfvAijN/tAK0vlJbOnxncuzYJC6pwoS?= =?us-ascii?Q?d186QtMqp5dZtFCB2uQWFHq+LS2Wkij9QgLWPXVjBlJKpin90obqbmSLww0m?= =?us-ascii?Q?eAon3YwBdpWO4ZaRrYYZr1GNYcIlc9PDV93VGBSllgiTupbd0A651JQLznvH?= =?us-ascii?Q?NY5v8n+kn2mJo1BLMDKjTVgAvIsziw1WStjq+E5TiP0GGQom5DUZpNNIahqP?= =?us-ascii?Q?EIpnnrKBDIlVe2ZkOJBtKzv56o+7vuwzrh12JJXWNoyoBfx6ddipLd+ulwIZ?= =?us-ascii?Q?/kQ+xdhytyvxJaTYBXQy+vE2sfPJBzY0spX4N4bGhzv0G0NwjUzmFbfQugJQ?= =?us-ascii?Q?XPlaOCRmwFr5XdXrA+JSSfjOfsJV8d/DEjYzuTBTyuM5Fg1kEAkK7W9BMpPP?= =?us-ascii?Q?vkvY2/corHliGAGP3gPw3WW0WYfOx550wJ0nsGUZWYlLCe6voNhG+2oN0kv2?= =?us-ascii?Q?8LNJAWi1Uu8XjFUyL+87jkjJn4wvcv35sev5lUBhFJUjmo6+Ss+jbMVicqSY?= =?us-ascii?Q?Bpgi4tB9bQcPqVuYjXbVwhvFMuTHVkxgJYM8cBj/AGVmbWzIqsWCRIrKI7uC?= =?us-ascii?Q?3umH4DSRNMwArGYheUSp7Cbt77zH3QA1AkfNplUA5vHxU2wQqqAwJtFz3yy3?= =?us-ascii?Q?KOf6E3WIPpEQqbdl1rZC0xuND8rvLsI9V7Q6ylykXLOAEMeObU5awa1Fffdx?= =?us-ascii?Q?QZv8qYkbszGPeelHC9ylBM1hCDofy7dTUnO7lIwndlXnaLQo1ESZwMh9JIum?= =?us-ascii?Q?8N+U4Vc0P4BdS41rF2y6gY9ag3XMeZ/hjLoHk1PGwa1xlCqoEIiHmEWb/8vu?= =?us-ascii?Q?4HPJQQcoMCVyFzWun9nwjykv92vZZfqwDsxwSsKjT0xLsPcJcbvT88DTlIkD?= =?us-ascii?Q?NJ0Q8cVgtkl+/4IHFcXTf8NSH/HOimo0lQmgHzAilqZXvQJzkp8qF7DY8Lxd?= =?us-ascii?Q?iekkMT9WsDl5+HennvLmU9Zgta4M6zDWu43N+juZZtJj/F25a82lFiSnqrRR?= =?us-ascii?Q?RkjaWY3P7b2XS+btyBamQ9648RW6MbHY2bjTtvZ4XFM1c2PBZNU7qKpohW9/?= =?us-ascii?Q?BxaWJfRd8dKwxSxZZvws2XO/ibi2deCewE1ZQYkzcZ+pzvlyRGdqPSK7vTwg?= =?us-ascii?Q?AmlEBka37a1niyoHYlYdvY9Vj7/xsFrDs8tcy3Eo98TRkuGZm9LTLa3Z/Qw0?= =?us-ascii?Q?386O+NduykwBTdqlNGZCAQrZVyN7Bb0EQclJwr8epIXyMVZWRnz3KRAncCl8?= =?us-ascii?Q?LzJKajSEi/RmxL7bDxswL1cQrB2dNkkFlgQmYQ2yB2CHe+iFvFAUxy88ZnRa?= =?us-ascii?Q?poyyW5CLDwSuLuFqelUNj6BrqyKoVaiqUEtTlFusAQe1IWdtnvm3H5ketlW3?= =?us-ascii?Q?AxS1uEpxEf1yHSNKcAkc9Qtuh/OR8VpNCRJYmZCqxrFnI7oyu2us2KDqOsZP?= =?us-ascii?Q?HB5gLKdHXSM0GLcKyBwrc8KANWTtOpFjyidLRTXWO8miiauv1H+xpSxapa0i?= =?us-ascii?Q?GF+3YLTGe2tzDR1M08TVoees9IaNbVmVczAXJmOvfYffE2amL+HCjmi89lAP?= =?us-ascii?Q?OBytQQTqiLpGU59i1cbc0hHrKLGjZ9TuQwuO3OYmw68ZSooqA+MnLZbswigz?= =?us-ascii?Q?joCsExHUbXUqpUV0aDiCZH1XuHz28p9b7/8SVhXlz3q9NUn1FbT+2u3Xb6BH?= =?us-ascii?Q?8Bi5M5pnMw=3D=3D?= X-OriginatorOrg: Nvidia.com X-MS-Exchange-CrossTenant-Network-Message-Id: bdb36210-6177-44ca-773b-08decc15b87d X-MS-Exchange-CrossTenant-AuthSource: CH2PR12MB5001.namprd12.prod.outlook.com X-MS-Exchange-CrossTenant-AuthAs: Internal X-MS-Exchange-CrossTenant-OriginalArrivalTime: 17 Jun 2026 02:11:20.5169 (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: pTcVI4/Sk6fBCRk+z3NH3HKcE7ESV94bc6CWT3DsTQEt5Ygpx7tD8EyD8q+p8OM9n5KjGHDHMzJBgqA8Hko8qw== X-MS-Exchange-Transport-CrossTenantHeadersStamped: MN6PR12MB8472 On Tue, Jun 16, 2026 at 03:07:53PM +0200, David Hildenbrand (Arm) wrote: > On 6/16/26 14:30, Lance Yang wrote: > > > > On Tue, Jun 16, 2026 at 06:34:36AM +0000, Wei Yang wrote: > > [...] > >> diff --git a/mm/page_vma_mapped.c b/mm/page_vma_mapped.c > >> index 2ccbabfb2cc1..21635fab209c 100644 > >> --- a/mm/page_vma_mapped.c > >> +++ b/mm/page_vma_mapped.c > >> @@ -243,40 +243,28 @@ bool page_vma_mapped_walk(struct page_vma_mapped_walk *pvmw) > >> */ > >> pmde = pmdp_get_lockless(pvmw->pmd); > >> > >> - if (pmd_trans_huge(pmde) || pmd_is_migration_entry(pmde)) { > >> - pvmw->ptl = pmd_lock(mm, pvmw->pmd); > >> - pmde = *pvmw->pmd; > >> - if (!pmd_present(pmde)) { > >> - softleaf_t entry; > >> - > >> - if (!thp_migration_supported() || > >> - !(pvmw->flags & PVMW_MIGRATION)) > >> - return not_found(pvmw); > >> - entry = softleaf_from_pmd(pmde); > >> - > >> - if (!softleaf_is_migration(entry) || > >> - !check_pmd(softleaf_to_pfn(entry), pvmw)) > >> - return not_found(pvmw); > >> - return true; > >> - } > >> - if (likely(pmd_trans_huge(pmde))) { > >> - if (pvmw->flags & PVMW_MIGRATION) > >> - return not_found(pvmw); > >> - if (!check_pmd(pmd_pfn(pmde), pvmw)) > >> - return not_found(pvmw); > >> - return true; > >> - } > >> - /* THP pmd was split under us: handle on pte level */ > >> - spin_unlock(pvmw->ptl); > >> - pvmw->ptl = NULL; > >> - } else if (!pmd_present(pmde)) { > >> - const softleaf_t entry = softleaf_from_pmd(pmde); > >> - > >> - if (softleaf_is_device_private(entry)) { > >> - pvmw->ptl = pmd_lock(mm, pvmw->pmd); > >> - return true; > >> - } > >> + if (pmd_present(pmde)) { > >> + if (!pmd_leaf(pmde)) > >> + goto pte_table; > >> + if (pvmw->flags & PVMW_MIGRATION) > >> + return not_found(pvmw); > >> + if (!check_pmd(pmd_pfn(pmde), pvmw)) > >> + return not_found(pvmw); > >> + } else if (pmd_is_migration_entry(pmde)) { > >> + softleaf_t entry = softleaf_from_pmd(pmde); > >> + > >> + if (!(pvmw->flags & PVMW_MIGRATION)) > >> + return not_found(pvmw); > > > > Looked at history a bit, and I wonder if this changed something old > > here ... > > > > Since 616b8371539a ("mm: thp: enable thp migration in generic path"), PMD > > migration handling took PTL before doing PVMW_MIGRATION/PFN checks, > > including not_found() cases. So lockless PMD read was just a filter ... > > > > With this fix, true case gets final pmd_same() check, but this > > not_found() case happens before taking PTL. > > > > So a !PVMW_MIGRATION walker could race with someone, e.g. > > remove_migration_pmd(): we make the not_found() decision from old PMD > > value that still says "migration", while real *pvmw->pmd may already be > > present again. We return without ever taking PTL :) > > > > Not sure about practical fallout, but should these PMD-level not_found() > > cases also take PTL and restart if PMD changed? > I was hoping that we could so something similar to the PTE case. > > In map_pte(), we check whether the PMD changed, which is slightly different. > > The actual check happens in check_pte() after grabbing the PTL. > > For the case you describe, map_pte() would find !pte_none(ptent) ... > !pte_present(ptent) and !is_migration, and effectively grab the lock and proceed > to check_pte(). > > In check_pte() we re-check under lock indeed. > Thinking of the practical fallout, not finding the PMD for a non migration worker should be OK. Is there a case where it's not OK to report the old state. Balbir