Failed to start libvirt guest: libvirtError: unsupported configuration: Unknown PCI device <driver name='vhost'/> has been specified

Issue

• When trying to create a heat stack constituted of VMs using SR-IOV ports, the VMs are failing to start with the following error message:

Failed to start libvirt guest: libvirtError: unsupported configuration: Unknown PCI device <driver name='vhost'/> has been specified

• The HOT template does feature the configuration "binding_type: direct" to specify SR-IOV interfaces.

• The samething happens if we try to create the VM manually without using heat.

• The instance in question should be using SR-IOV ports, but if we look at the generated XML, we can see the following:

    <interface type="hostdev" managed="yes">
      <mac address="fa:16:3e:91:82:82"/>
      <driver name="vhost" rx_queue_size="512"/>
      <source>
        <address type="pci" domain="0x0000" bus="0x37" slot="0x03" function="0x4"/>
      </source>
      <vlan>
        <tag id="1070"/>
      </vlan>
    </interface>
    <interface type="hostdev" managed="yes">
      <mac address="fa:16:3e:02:59:a8"/>
      <driver name="vhost" rx_queue_size="512"/>
      <source>
        <address type="pci" domain="0x0000" bus="0x37" slot="0x0b" function="0x5"/>
      </source>
      <vlan>
        <tag id="1070"/>
      </vlan>
    </interface>

instead of:

    <interface type="hostdev" managed="yes">
      <mac address="fa:16:3e:91:82:82"/>
      <driver name="vfio"/>
      <source>
        <address type="pci" domain="0x0000" bus="0x37" slot="0x03" function="0x4"/>
      </source>
      <vlan>
        <tag id="1070"/>
      </vlan>
    </interface>
    <interface type="hostdev" managed="yes">
      <mac address="fa:16:3e:02:59:a8"/>
      <driver name="vfio"/>
      <source>
        <address type="pci" domain="0x0000" bus="0x37" slot="0x0b" function="0x5"/>
      </source>
      <vlan>
        <tag id="1070"/>
      </vlan>
    </interface>