Re: [Xen-devel] [Intel-gfx] [Announcement] 2015-Q3 release of XenGT - a Mediated Graphics Passthrough Solution from Intel

[Stefano Stabellini <stefano.stabellini@xxxxxxxxxxxxx>]

On Thu, 19 Nov 2015, Paolo Bonzini wrote:
> On 19/11/2015 16:32, Stefano Stabellini wrote:
> > > In addition to Kevin's replies, I have a high-level question: can VFIO
> > > be used by QEMU for both KVM and Xen?
> > 
> > No. VFIO cannot be used with Xen today. When running on Xen, the IOMMU
> > is owned by Xen.
> 
> I don't think QEMU command line compatibility between KVM and Xen should
> be a design goal for GVT-g.

Right, I agree.

In fact I don't want my comment to be taken as "VFIO should not be used
at all". I only meant to reply to the question. I think it is unlikely
to be the best path for Xen, but it could very well be the right answer
for KVM.


> Nevertheless, it shouldn't be a problem to use a "virtual" VFIO (which
> doesn't need the IOMMU, because it uses the MMU in the physical GPU)
> even under Xen.

That could be true, but I would expect some extra work to be needed to
make use of VFIO on Xen. Also it might cause some duplication of
functionalities with the current Xen passthrough code base.

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