[PATCH v3 6/6] docs: add s390-pv documentation

[Erik Skultety]

...

> > +Example guest definition without launchSecurity
> > +===============================================
> > +
> > +Minimal domain XML for a protected virtualization guest using the
> > +``iommu='on'`` setting for each virtio device.
> 
> I don't know how s390-pv works but for example with AMD SEV it is
> required to use `iommu='on'` otherwise the device is not visible inside
> the VM so I would like to make sure there is no misunderstanding and
> it is correct.

Can you elaborate on how is the device not visible in the VM? IIRC 'iommu=on'
makes sure that the guest virtio driver is able to negotiate the
VIRTIO_F_IOMMU_PLATFORM feature which in connection with the correct IOMMU model
setting makes SEV work with virtio and IOMMU
(AFAIR OVMF has a dedicated SEV iommu driver).

Therefore, that flag should have nothing to do with device visibility, in fact
in x86_64's case it will be a PCI device, so you'll always be able to list
those.

Regards,
Erik