Check if virtio-blk-data-plane is being used by the KVM guest virtual file-backed raw format image disks.
gstanden@vmem1:~$ sudo virsh qemu-monitor-command --hmp oracle631 'info qtree' | grep x-data
x-data-plane = true
x-data-plane = true
gstanden@vmem1:~$ sudo virsh qemu-monitor-command --hmp oracle632 'info qtree' | grep x-data
x-data-plane = true
x-data-plane = true
gstanden@vmem1:~$ sudo virsh qemu-monitor-command --hmp oracle651 'info qtree' | grep x-data
x-data-plane = true
x-data-plane = true
x-data-plane = true
gstanden@vmem1:~$
Additional notes are available here at Stefan Hajnoczi blog.