On Thu, Oct 23, 2014 at 07:34:16AM +1100, Benjamin Herrenschmidt wrote: > On Wed, 2014-10-22 at 16:17 +0200, Jan Kiszka wrote: > > I thought about this again, and I'm not sure anymore if we can use > > ACPI > > to "black-list" the incompatible virtio devices. Reason: hotplug. To > > my > > understanding, the ACPI DRHD tables won't change during runtime when a > > device shows up or disappears. We would have to isolate virtio devices > > from the rest of the system by using separate buses for it (and avoid > > listing those in any DRHD table) and enforce that they only get > > plugged > > into those buses. I suppose that is not desirable. > > > > Maybe it's better to fix virtio /wrt IOMMUs. > > I always go back to my initial proposal which is to define that current > virtio always bypass any iommu (which is what it does really) and have > it expose via a new capability if that isn't the case. That means fixing > that Xen thingy to allow qemu to know what to expose I assume but that > seems to be the less bad approach. > > Cheers, > Ben. >
OK so how does this work? If you want to run an existing guest, you use the old device. And presumably you blacklist virtio for nested virt then, unless a new capability is present? -- MST
