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Live migration should be terminated if the vhost-user backend crashes before the migration completes. Specifically, since the vhost device will be stopped when VM is stopped before the end of the live migration, in current implementation if the backend crashes, vhost-user device set_status() won't return failure, live migration won't perceive the disconnection between QEMU and the backend. When the VM is migrated to the destination, the inflight IO will be resubmitted, and if the IO was completed out of order before, it will cause IO error. To fix this issue: 1. Add the return value to set_status() for VirtioDeviceClass. a. For the vhost-user device, return failure when the backend crashes. b. For other virtio devices, always return 0. 2. Return failure if vhost_dev_stop() failed for vhost-user device. If QEMU loses connection with the vhost-user backend, virtio set_status() can return failure to the upper layer, migration_completion() can handle the error, terminate the live migration, and restore the VM, so that inflight IO can be completed normally. Signed-off-by: Haoqian He <haoqian.he@smartx.com> Message-Id: <20250416024729.3289157-4-haoqian.he@smartx.com> Tested-by: Lei Yang <leiyang@redhat.com> Reviewed-by: Michael S. Tsirkin <mst@redhat.com> Signed-off-by: Michael S. Tsirkin <mst@redhat.com>