Comment 17 for bug 1845986

Reviewed: https://review.opendev.org/685756
Committed: https://git.openstack.org/cgit/openstack/nova/commit/?id=0662697bbf982b60c595d363324b9b6e501f9ded
Submitter: Zuul
Branch: stable/train

commit 0662697bbf982b60c595d363324b9b6e501f9ded
Author: Boris Bobrov <email address hidden>
Date: Fri Nov 29 13:40:00 2019 +0100

    Also enable iommu for virtio controllers and video in libvirt

    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
    (cherry picked from commit 1a88d35cb161df34f11ce17fed3b62621f774672)