Commit 9d7bd0826f introduced a new 'use-disabled-flag' property
set to true by default.
To allow the migration, we set this property to false in the hw_compat,
but in the wrong place (hw_compat_4_1).
Since commit 9d7bd0826f was released with QEMU 5.0, we move
'use-disabled-flag' property to hw_compat_4_2, so 4.2 machine types
will have the pre-patch behavior and the migration can work.
The issue was discovered with vhost-vsock device and 4.2 machine
type without running any kernel in the VM:
$ qemu-4.2 -M pc-q35-4.2,accel=kvm \
-device vhost-vsock-pci,guest-cid=4 \
-monitor stdio -incoming tcp:0:3333
$ qemu-5.2 -M pc-q35-4.2,accel=kvm \
-device vhost-vsock-pci,guest-cid=3 \
-monitor stdio
(qemu) migrate -d tcp:0:3333
# qemu-4.2 output
qemu-system-x86_64: Failed to load virtio-vhost_vsock:virtio
qemu-system-x86_64: error while loading state for instance 0x0 of device '0000:00:03.0/virtio-vhost_vsock'
qemu-system-x86_64: load of migration failed: No such file or directory
Reported-by: Jing Zhao <jinzhao@redhat.com>
Buglink: https://bugzilla.redhat.com/show_bug.cgi?id=1907255
Fixes: 9d7bd0826f ("virtio-pci: disable vring processing when bus-mastering is disabled")
Cc: mdroth@linux.vnet.ibm.com
CC: qemu-stable@nongnu.org
Signed-off-by: Stefano Garzarella <sgarzare@redhat.com>
Message-Id: <20210108171252.209502-1-sgarzare@redhat.com>
Reviewed-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
c126b4c57e