$> virsh qemu-monitor-command cvm5 --hmp info qom-tree |& head -3
/machine (pc-i440fx-2.10-machine)
  /unattached (container)
    /device[0] (Haswell-noTSX-x86_64-cpu)

$> virsh qemu-monitor-command cvm5 --pretty '{ "execute": "qom-get", "arguments": { "path": "/machine/unattached/device[0]", "property": "pcid" } }'
{
  "return": true,
  "id": "libvirt-18"
}