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Peter Anvin" , Jonathan Corbet , "Shuah Khan" , Peter Shier , "Jim Mattson" , Ricardo Koller , "Ira Weiny" , Fuad Tabba CC: , , , , , , , Shivank Garg , Sashiko X-Mailer: b4 0.15-dev-47d62 X-Developer-Signature: v=1; a=ed25519-sha256; t=1785912059; l=3935; i=shivankg@amd.com; s=20260518; h=from:subject:message-id; bh=Hx9UYtC7m81cRsUZoyk/6NCu3lSkUrBZZZ2qPIwWefg=; b=Fk56lSaOnFisB+qDkjH/DtKWve4VGfa7qvMwXYHElvxiK+c3yEFe/lnluiAQ3BI/O9OE4xshE BylNPbHkQvdDYvJyQFLjP7CrBuVu71gnlAYfPfBdXEvUbBu8oCF9NGb X-Developer-Key: i=shivankg@amd.com; a=ed25519; pk=2l2QGTeXuGkZTtfmx0nPQU8iFZfjYmX/ymMojitevx4= X-ClientProxiedBy: satlexmb08.amd.com (10.181.42.217) To satlexmb07.amd.com (10.181.42.216) X-EOPAttributedMessage: 0 X-MS-PublicTrafficType: Email X-MS-TrafficTypeDiagnostic: MWH0EPF000C6189:EE_|DS7PR12MB5744:EE_ X-MS-Office365-Filtering-Correlation-Id: 949bbe7b-f0ba-466b-244f-08def2bc9879 X-MS-Exchange-SenderADCheck: 1 X-MS-Exchange-AntiSpam-Relay: 0 X-Microsoft-Antispam: BCL:0;ARA:13230040|82310400026|36860700016|376014|1800799024|7416014|23010399003|56012099006|5023799004|11063799006|22082099003|18002099003|10067099003|13003099007|921020; X-Microsoft-Antispam-Message-Info: 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 X-Forefront-Antispam-Report: CIP:165.204.84.17;CTRY:US;LANG:en;SCL:1;SRV:;IPV:NLI;SFV:NSPM;H:satlexmb07.amd.com;PTR:InfoDomainNonexistent;CAT:NONE;SFS:(13230040)(82310400026)(36860700016)(376014)(1800799024)(7416014)(23010399003)(56012099006)(5023799004)(11063799006)(22082099003)(18002099003)(10067099003)(13003099007)(921020);DIR:OUT;SFP:1101; X-MS-Exchange-AntiSpam-MessageData-ChunkCount: 1 X-MS-Exchange-AntiSpam-MessageData-0: datV/Epw51BdEE8tvFA3DYlsVLX1Hsu/dYeilTst+ZuO6wTU6ugGH/lvMp5Qd8ddWVf1i6Xtf3ac0CdJ+ARRrMKm50o3J/t5e0KL2QcvoJ47j5fA1mvM9wMvdE1gG6wINEXyYtVScBposg095kIjtP/kavd+ugfDKdnPEach7Qb6pCr6ITgot78eCUaK/aQhfJsxq+73C+qMeEv8dt9eHpA1+9L97OTZI/glAQ5oCYE7B82Sk3pikeM+KDFGnMQqLPYhziUf6dJarTyyfpbzUS+398QMCm7CdMnFvnPTGdkhAksR0kkwDS7bsRQyDYUhHxeLpuIi09EFvK2lo027WA60uccmxJvtE22SfJD48M5mMxaQjB1IMFU/uNF7gnvKzHjebxymjve1zIUWIfYkfMA36tUlSmJWxJw4JGlzvpAEpUTwlDX3rMf3+uFSINn7 X-OriginatorOrg: amd.com X-MS-Exchange-CrossTenant-OriginalArrivalTime: 05 Aug 2026 06:41:35.7700 (UTC) X-MS-Exchange-CrossTenant-Network-Message-Id: 949bbe7b-f0ba-466b-244f-08def2bc9879 X-MS-Exchange-CrossTenant-Id: 3dd8961f-e488-4e60-8e11-a82d994e183d X-MS-Exchange-CrossTenant-OriginalAttributedTenantConnectingIp: TenantId=3dd8961f-e488-4e60-8e11-a82d994e183d;Ip=[165.204.84.17];Helo=[satlexmb07.amd.com] X-MS-Exchange-CrossTenant-AuthSource: MWH0EPF000C6189.namprd02.prod.outlook.com X-MS-Exchange-CrossTenant-AuthAs: Anonymous X-MS-Exchange-CrossTenant-FromEntityHeader: HybridOnPrem X-MS-Exchange-Transport-CrossTenantHeadersStamped: DS7PR12MB5744 kvm_gmem_unbind() skips mapping->invalidate_lock when the guest_memfd file is already dying. All other paths that modify f->bindings hold that lock. kvm_gmem_invalidate_{start,end}() checks f->bindings independently to decide whether to begin or end KVM MMU invalidations. So, the bindings must remain stable between the two calls. If a binding is removed in that window, start increments mmu_invalidate_in_progress but end does not decrement it. Example, unbind race with memory failure: CPU 0: memory failure CPU 1: memslot delete ---------------------------------- --------------------------- (guest_memfd file is dying) kvm_gmem_error_folio() kvm_gmem_invalidate_start() finds binding mmu_invalidate_in_progress++ kvm_gmem_unbind() get_file_active() fails store NULL in bindings kvm_gmem_invalidate_end() no binding found counter stays elevated mmu_invalidate_retry() then returns 1 forever, so guest page faults retry without ever installing a mapping and the guest hangs. Take the invalidate lock in the dying-file path too. This prevents unbind from removing a binding and leaking mmu_invalidate_in_progress. This is safe because any caller that reaches this path holds slots_lock, so kvm_gmem_release() cannot nullify the slots->gmem.file, until kvm_gmem_unbind() finishes. Reported-by: Sashiko Closes: https://lore.kernel.org/all/20260728092027.225CF1F000E9@smtp.kernel.org Fixes: ae431059e75d ("KVM: guest_memfd: Remove bindings on memslot deletion when gmem is dying") Signed-off-by: Shivank Garg --- virt/kvm/guest_memfd.c | 23 ++++++++++++++--------- 1 file changed, 14 insertions(+), 9 deletions(-) diff --git a/virt/kvm/guest_memfd.c b/virt/kvm/guest_memfd.c index db57c5766ab6..45cbdf4801ec 100644 --- a/virt/kvm/guest_memfd.c +++ b/virt/kvm/guest_memfd.c @@ -721,6 +721,8 @@ static void __kvm_gmem_unbind(struct kvm_memory_slot *slot, struct gmem_file *f) void kvm_gmem_unbind(struct kvm_memory_slot *slot) { + struct file *gmem_file; + /* * Nothing to do if the underlying file was _already_ closed, as * kvm_gmem_release() invalidates and nullifies all bindings. @@ -733,21 +735,24 @@ void kvm_gmem_unbind(struct kvm_memory_slot *slot) /* * However, if the file is _being_ closed, then the bindings need to be * removed as kvm_gmem_release() might not run until after the memslot - * is freed. Note, modifying the bindings is safe even though the file - * is dying as kvm_gmem_release() nullifies slot->gmem.file under + * is freed. Note, dereferencing the dying file is safe as + * kvm_gmem_release() nullifies slot->gmem.file under * slots_lock, and only puts its reference to KVM after destroying all * bindings. I.e. reaching this point means kvm_gmem_release() hasn't * yet destroyed the bindings or freed the gmem_file, and can't do so * until the caller drops slots_lock. */ - if (!file) { - __kvm_gmem_unbind(slot, slot->gmem.file->private_data); - return; - } + gmem_file = file ?: slot->gmem.file; - filemap_invalidate_lock(file->f_mapping); - __kvm_gmem_unbind(slot, file->private_data); - filemap_invalidate_unlock(file->f_mapping); + /* + * Take the invalidate lock even for a dying file. Otherwise, + * kvm_gmem_invalidate_start() can find the binding and increment + * mmu_invalidate_in_progress while kvm_gmem_invalidate_end() misses + * the removed binding and skips decrement. + */ + filemap_invalidate_lock(gmem_file->f_mapping); + __kvm_gmem_unbind(slot, gmem_file->private_data); + filemap_invalidate_unlock(gmem_file->f_mapping); } /* Returns a locked folio on success. */ -- 2.43.0