Re: [Qemu-devel] [PATCH RFC 00/11] qemu: towards virtio-1 host support

[Benjamin Herrenschmidt]

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.