[libvirt] Libvirt error in Openstack Tempest attaching disk on arm64 system

I am running Openstack Tempest on an arm64 platform and am seeing some test failures related to attaching volumes to an instance. This is an example of the disk XML generated by one of the tests: <disk type="block" device="disk"><driver name="qemu" type="raw" cache="none"/<source dev="/dev/disk/by-path/ip-10.7.1.2:3260-iscsi-iqn.2010-10.org.openstack:volume-5a204339-80cb-4d06-aecf-2a8a2c970b0e-lun-1"/><target bus="virtio" dev="vdb"/><serial>5a204339-80cb-4d06-aecf-2a8a2c970b0e</serial></disk> The test is failing with the error "XML error: No PCI buses available". I am trying to find the relevent source locations for this functionality in either in the nova libvirt driver or in the libvirt source itself. I am not sure why I am getting an error about no PCI buses when the bus specified in the XML is "virtio". I would appreciate any pointers / help. Thank you, Clark L