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

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Date:	Thu, 19 Nov 2015 16:12:06 +0000
From:	Stefano Stabellini <stefano.stabellini@...citrix.com>
To:	Paolo Bonzini <pbonzini@...hat.com>
CC:	Stefano Stabellini <stefano.stabellini@...citrix.com>,
	Jike Song <jike.song@...el.com>,
	Alex Williamson <alex.williamson@...hat.com>,
	"Tian, Kevin" <kevin.tian@...el.com>,
	"xen-devel@...ts.xen.org" <xen-devel@...ts.xen.org>,
	"igvt-g@...1.01.org" <igvt-g@...1.01.org>,
	"intel-gfx@...ts.freedesktop.org" <intel-gfx@...ts.freedesktop.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"White, Michael L" <michael.l.white@...el.com>,
	"Dong, Eddie" <eddie.dong@...el.com>,
	"Li, Susie" <susie.li@...el.com>,
	"Cowperthwaite, David J" <david.j.cowperthwaite@...el.com>,
	"Reddy, Raghuveer" <raghuveer.reddy@...el.com>,
	"Zhu, Libo" <libo.zhu@...el.com>,
	"Zhou, Chao" <chao.zhou@...el.com>,
	"Wang, Hongbo" <hongbo.wang@...el.com>,
	"Lv, Zhiyuan" <zhiyuan.lv@...el.com>,
	qemu-devel <qemu-devel@...gnu.org>,
	Gerd Hoffmann <kraxel@...hat.com>
Subject: Re: [Intel-gfx] [Announcement] 2015-Q3 release of XenGT - a Mediated
 Graphics Passthrough Solution from Intel

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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