On Wed, Oct 22, 2014 at 04:17:40PM +0200, Jan Kiszka wrote: > On 2014-10-22 10:44, Michael S. Tsirkin wrote: > > On Wed, Oct 08, 2014 at 11:04:28AM +0200, Cornelia Huck wrote: > >> On Tue, 07 Oct 2014 18:24:22 -0700 > >> Andy Lutomirski <l...@amacapital.net> wrote: > >> > >>> On 10/07/2014 07:39 AM, Cornelia Huck wrote: > >>>> This patchset aims to get us some way to implement virtio-1 compliant > >>>> and transitional devices in qemu. Branch available at > >>>> > >>>> git://github.com/cohuck/qemu virtio-1 > >>>> > >>>> I've mainly focused on: > >>>> - endianness handling > >>>> - extended feature bits > >>>> - virtio-ccw new/changed commands > >>> > >>> At the risk of some distraction, would it be worth thinking about a > >>> solution to the IOMMU bypassing mess as part of this? > >> > >> I think that is a whole different issue. virtio-1 is basically done - we > >> just need to implement it - while the IOMMU/DMA stuff certainly needs > >> more discussion. Therefore, I'd like to defer to the other discussion > >> thread here. > > > > I agree, let's do a separate thread for this. > > I also think it's up to the hypervisors at this point. > > People talked about using ACPI to report IOMMU bypass > > to guest. > > If that happens, we don't need a feature bit. > > 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.
That's reasonable I think. > Maybe it's better to fix virtio /wrt IOMMUs. > > Jan Yes but this seems unlikely for 2.2: The wish to run old guests with iommu remains. So we'll need to support iommu bypass on the host, and so as a minimum new guest needs to detect such bypass host and fail. Unrelated: we also need to teach vhost and dataplane virtio to get mappings from the iommu. > -- > Siemens AG, Corporate Technology, CT RTC ITP SES-DE > Corporate Competence Center Embedded Linux
