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charset=UTF-8 Date: Sat, 12 Sep 2026 09:50:30 -0400 Message-Id: From: "Zi Yan" Subject: Re: [PATCH v2 1/2] mm/mempolicy: use vm_normal_folio_pmd() in queue_folios_pmd() Cc: , , , , , , , , , , , , , , , , "sashiko-bot" , To: "Gregory Price" , X-Mailer: aerc 0.22.0 References: <20260912034833.2952750-1-gourry@gourry.net> <20260912034833.2952750-2-gourry@gourry.net> In-Reply-To: <20260912034833.2952750-2-gourry@gourry.net> X-ClientProxiedBy: BL1PR13CA0241.namprd13.prod.outlook.com (2603:10b6:208:2ba::6) 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_|IA0PPF12042BF6F:EE_ X-MS-Office365-Filtering-Correlation-Id: d2dbdff5-0719-4903-f666-08df10d4cfae X-MS-Exchange-SenderADCheck: 1 X-MS-Exchange-AntiSpam-Relay: 0 X-Microsoft-Antispam: BCL:0;ARA:13230040|376014|7416014|1800799024|366016|23010399003|18002099003|22082099003|56012099006|11063799006|4143699003|10067099003; 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> > With a stand-in module for the driver: > > BUG: unable to handle page fault for address: fffff96dc0000008 > RIP: 0010:queue_folios_pte_range+0xaf/0x440 > walk_pgd_range+0x52b/0xaf0 > __walk_page_range+0x6a/0x1d0 > walk_page_range_mm_unsafe+0x193/0x230 > queue_pages_range+0x64/0xa0 > do_mbind+0x25e/0x640 > > queue_folios_pmd(), inlined above, calls pmd_folio() on that PMD. The pf= n > is raw MMIO with no memmap entry, so the folio lands in unpopulated > vmemmap. Neither guard stops the walk: > > walk_page_test() skips VM_PFNMAP, but queue_pages_walk_ops > supplies ->test_walk, so it never runs > queue_pages_test_walk() honours vma_migratable(), but only while > MPOL_MF_STRICT is clear > > A VM_MIXEDMAP vma needs neither flag, being vma_migratable(), so plain > mbind(MPOL_MF_MOVE) reaches this too - and there the bad folio carries on > into migrate_folio_add() and folio_isolate_lru(). mshv_vtl_low is such a > mapping. > > Use vm_normal_folio_pmd() and skip on NULL, as the PTE loop in > queue_folios_pte_range() already does with vm_normal_folio(). On the NUL= L > path, retain ACTION_CONTINUE handling for the huge zero PMD. > > mbind(MPOL_MF_STRICT) over a PMD mapped VM_PFNMAP region now returns 0 > rather than -EIO. The PTE loop already returned 0 there. > > Fixes: 3c8e44c9b369 ("mm: mark special bits for huge pfn mappings when in= ject") > Reported-by: sashiko-bot > Closes: https://sashiko.dev/#/patchset/20260817220810.1175596-1-gourry%40= gourry.net > Cc: stable@vger.kernel.org > Assisted-by: LLM > Signed-off-by: Gregory Price (Meta) > Acked-by: David Hildenbrand (Arm) > --- > mm/mempolicy.c | 16 +++++++++------- > 1 file changed, 9 insertions(+), 7 deletions(-) > LGTM. Reviewed-by: Zi Yan --=20 Best Regards, Yan, Zi