Ie54fca066f33 added logic to libvirt/designer.py for enabling iommu
for certain devices where virtio is used. This is required for AMD
SEV[0]. However it missed two cases.
Firstly, a SCSI controller can have the model as 'virtio-scsi', e.g.:
<controller type='scsi' index='0' model='virtio-scsi'>
As with other virtio devices, here a child element needs to be added
to the config when SEV is enabled:
<driver iommu="on" />
We do not need to cover the case of a controller with type
'virtio-serial' now, since even though it is supported by libvirt, it
is not currently used anywhere in Nova.
Secondly, a video device can be virtio, e.g. when vgpus are in use:
<video>
<model type='virtio'/>
</video>
Also take this opportunity to clarify the corresponding documentation
around disk bus options.
[0] http://specs.openstack.org/openstack/nova-specs/specs/train/approved/amd-sev-libvirt-support.html#proposed-change
Partial-Bug: #1845986
Change-Id: I626c35d1653e6a25125320032d0a4a0c67ab8bcf
1a88d35cb1