this step is not strictly necessary anymore. by using nodedev-define, the  element can be omitted and a uuid is auto-generated, this does also apply to the section about vfio_ap crypto domain attachment. in those cases, in order to define the hostdev, the generated uuid can be retrieved via virsh nodedev-dumpxml :

# virsh nodedev-dumpxml mdev_8f9c4a73_1411_48d2_895d_34db9ac18f85_matrix
<device>
  <name>mdev_8f9c4a73_1411_48d2_895d_34db9ac18f85_matrix</name>
  <parent>ap_matrix</parent>
  <capability type='mdev'>
    <type id='vfio_ap-passthrough'/>
    <uuid>8f9c4a73-1411-48d2-895d-34db9ac18f85</uuid>
    <iommuGroup number='0'/>
    <attr name='assign_adapter' value='0x02'/>
    <attr name='assign_domain' value='0x002b'/>
  </capability>
</device>







Reported by: smitterl

https://access.redhat.com/documentation/en-us/red_hat_enterprise_linux/8/html/configuring_and_managing_virtualization/managing-virtual-devices_configuring-and-managing-virtualization#annotations:f9895e90-b121-44b0-9bd8-6160aecf94ea