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Received: from BL0PR12MB2370.namprd12.prod.outlook.com (2603:10b6:207:47::27) by LV2PR12MB5725.namprd12.prod.outlook.com (2603:10b6:408:14c::12) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id 15.21.223.18; Tue, 21 Jul 2026 10:00:34 +0000 Received: from BL0PR12MB2370.namprd12.prod.outlook.com ([fe80::86cf:c3ec:2cf5:74c8]) by BL0PR12MB2370.namprd12.prod.outlook.com ([fe80::86cf:c3ec:2cf5:74c8%5]) with mapi id 15.21.0223.017; Tue, 21 Jul 2026 10:00:34 +0000 From: Richard Cheng To: catalin.marinas@arm.com, will@kernel.org, jic23@kernel.org Cc: ryan.roberts@arm.com, ardb@kernel.org, kevin.brodsky@arm.com, anshuman.khandual@arm.com, yang@os.amperecomputing.com, chaitanyas.prakash@arm.com, linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org, linux-cxl@vger.kernel.org, newtonl@nvidia.com, kristinc@nvidia.com, mochs@nvidia.com, kaihengf@nvidia.com, kobak@nvidia.com, Richard Cheng Subject: [PATCH v2] arm64/mm: Check the requested PFN range during memory removal Date: Tue, 21 Jul 2026 18:00:26 +0800 Message-ID: <20260721100026.10408-1-icheng@nvidia.com> X-Mailer: git-send-email 2.50.1 Content-Transfer-Encoding: 8bit Content-Type: text/plain X-ClientProxiedBy: TPYP295CA0036.TWNP295.PROD.OUTLOOK.COM (2603:1096:7d0:7::8) To BL0PR12MB2370.namprd12.prod.outlook.com (2603:10b6:207:47::27) MIME-Version: 1.0 X-MS-PublicTrafficType: Email X-MS-TrafficTypeDiagnostic: BL0PR12MB2370:EE_|LV2PR12MB5725:EE_ X-MS-Office365-Filtering-Correlation-Id: 109380f2-b8bb-454c-c1db-08dee70ee7e2 X-MS-Exchange-SenderADCheck: 1 X-MS-Exchange-AntiSpam-Relay: 0 X-Microsoft-Antispam: BCL:0;ARA:13230040|1800799024|366016|23010399003|376014|7416014|18002099003|10067099003|56012099006|11063799006; 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When the loop completes, pfn is at or beyond end_pfn. Passing it to can_unmap_without_split() therefore checks a range after the one being offlined. Consequently, a valid request can be rejected based on the following range, while a request that would split a leaf mapping can be accepted if the shifted range can be unmapped without a split. This was observed with CXL DAX memory, where the final memory block was incorrectly allowed to be offlined. Pass arg->start_pfn into can_unmap_without_split() so it checks the requested range. Fixes: 95a58852b0e5 ("arm64/mm: Reject memory removal that splits a kernel leaf mapping") Signed-off-by: Richard Cheng Reviewed-by: Anshuman Khandual --- Changelog: V1->v2: - Fix the typo in the subject - Clarify how pfn advances and which range was incorrectly checked The bug occurred on a machine with CXL Type-3 device. Branch: cxl-next Before 95a58852b0e5: """ $ sudo echo offline > memory557056/state write error: Operation not permitted $ sudo dmesg ---[snip]--- [440008000000 440010000000] splits a leaf entry in linear map $ sudo echo offline > memory558079/state $ cat memory558079/state offline """ After: """ $ sudo echo offline > memory557056/state write error: Operation not permitted [440000000000 440008000000] splits a leaf entry in linear map $ sudo echo offline > memory558079/state write error: Operation not permitted [441ff8000000 442000000000] splits a leaf entry in linear map """ My fix corrects the checked range and prevents the false acceptance. Best regards, Richard Cheng. --- arch/arm64/mm/mmu.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/arch/arm64/mm/mmu.c b/arch/arm64/mm/mmu.c index a25d8beacc83..18a8b0d3714e 100644 --- a/arch/arm64/mm/mmu.c +++ b/arch/arm64/mm/mmu.c @@ -2194,7 +2194,7 @@ static int prevent_memory_remove_notifier(struct notifier_block *nb, } } - if (!can_unmap_without_split(pfn, arg->nr_pages)) + if (!can_unmap_without_split(arg->start_pfn, arg->nr_pages)) return NOTIFY_BAD; return NOTIFY_OK; base-commit: 5ca04f3ba91f1773bbd5da6d9c654ccc1ba7831d -- 2.43.0