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X-MS-Exchange-AntiSpam-MessageData-ChunkCount: 1 X-MS-Exchange-AntiSpam-MessageData-0: omMO8JjKLnjpBJslYfDhbDJbuLeV5t6wD1iyMPeLF2Vqd63S3ikgt0E/uBu5zUhWZd5AKPy1bCygOwUjxqtWo2y4coI2u05JT31hgGfJWRn7TKI3UzDWDfDzAhKXdkohnoDu+aku6oaOAmyJc2kourRaLahMVZRK++FJ05i4mXmYtIG9QOBLc3QKaBt2GPv/5SiVF6YRPrIUZJyYH3adVkgET65JWmC1AX2R9Uw89OKlWzYxuR1csXFLFkQZJGD+QtPUDcaIf96mDHy6UxUnOPlrbiJ63G4TYtVmYvxu1mB69iYy0bVlgRohcq5wCjDFpLK1qjKdkD4SynOSRc9+5FOYJqVP5LMwXprC+DFw+bnUjt/b1/tLSkAAzRc6ZrsHx3bcOnLkbI83OqbSCwbFHHpzBGl4IMw0TtR8P4tKSe9Eza9CzVoqZU2UW0o39rJf X-ExternalRecipientOutboundConnectors: 0bc7f26d-0264-416e-a6fc-8352af79c58f X-OriginatorOrg: virtuozzo.com X-MS-Exchange-CrossTenant-OriginalArrivalTime: 02 Nov 2026 11:00:05.4706 (UTC) X-MS-Exchange-CrossTenant-Network-Message-Id: 446a4a33-2b0e-40c9-1b24-08df38d073b5 X-MS-Exchange-CrossTenant-Id: 0bc7f26d-0264-416e-a6fc-8352af79c58f X-MS-Exchange-CrossTenant-AuthSource: AMS1EPF00000097.eurprd02.prod.outlook.com X-MS-Exchange-CrossTenant-AuthAs: Anonymous X-MS-Exchange-CrossTenant-FromEntityHeader: Internet X-MS-Exchange-Transport-CrossTenantHeadersStamped: GV1PR08MB10908 > kvm_close() destroys the vCPUs, which unmaps their kvm_run areas, and the > coalesced MMIO ring lives in the kvm_run area of the first vCPU. Nothing > stops the RCU thread from flushing that ring at the same time: finalizing > a memory region of a freed flatview calls memory_region_transaction_begin= () > and thus kvm_flush_coalesced_mmio_buffer(). kvm_state is still set at > that point, so the flush reads the ring after it has been unmapped: >=20 > #0 kvm_flush_coalesced_mmio_buffer accel/kvm/kvm-all.c > #1 qemu_flush_coalesced_mmio_buffer > #2 memory_region_transaction_begin > #3 memory_region_finalize > ... > #10 flatview_destroy > #11 call_rcu_thread >=20 > while the main thread is in: >=20 > kvm_close -> cpu_remove_sync > vfio_kvm_device_close > vfio_cpr_kvm_close_notifier (MIG_EVENT_PRECOPY_DONE) >=20 > Seen as a SIGSEGV of the old QEMU during repeated cpr-exec of a VM with > a VFIO device. >=20 > Clear the ring pointer first, so that new flushes skip it, and wait for > the pending RCU callbacks before destroying the vCPUs. >=20 > Fixes: 7ed0919119b0 ("migration: close kvm after cpr") > Signed-off-by: Andrey Drobyshev Sashiko has reviewed this patch and found no issues. It looks great! --=20 Sashiko AI review =C2=B7 https://sashiko.vzint.dev/#/patchset/20261102-vfio= _v1-v6-0-9bc7cabc850d@virtuozzo.com?part=3D23