[libvirt] [PATCH v2 RESEND 00/12] PCI passthrough support on s390

[Andrea Bolognani]

On Thu, 2018-07-26 at 12:52 +0100, Daniel P. Berrangé wrote:
> On Thu, Jul 26, 2018 at 01:47:52PM +0200, Andrea Bolognani wrote:
> > On Thu, 2018-07-26 at 12:22 +0100, Daniel P. Berrangé wrote:
> > > From the libvirt side we must avoid any scenario where QEMU auto-adds
> > > devices behind our back. If adding a device requires adding a controller
> > > libvirt must do this explicitly and record it in the XML.
> > 
> > Definitely. My question was whether the corresponding zpci device
> > should be created as well...
> 
> I'm not sure I understand it fully, but it sounds like  zpci devices are
> providing info that is guest ABI sensitive, which would mean libvirt must
> control and record it. So from that POV we should create zpci devices

Making sure the guest-visible address is stable is taken care of
by the additional PCI address attributes uid and fid, which are
then used when creating the zpci device.

PCI controllers such as pci-bridge are, however, not visible to the
guest and as such it would be possible to skip the corresponding
zpci devices; it's been argued, though, that it's better to create
them regardless in order to maintain consistency.

-- 
Andrea Bolognani / Red Hat / Virtualization