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Date: Tue, 19 Apr 2016 19:04:43 +0300
From: "Michael S. Tsirkin" <mst@redhat.com>
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Subject: Re: [Qemu-devel] [PATCH RFC] fixup! virtio: convert to use DMA api
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To: Andy Lutomirski <luto@amacapital.net>
Cc: Cornelia Huck <cornelia.huck@de.ibm.com>, Christian Borntraeger <borntraeger@de.ibm.com>, "qemu-devel@nongnu.org Developers" <qemu-devel@nongnu.org>, David Woodhouse <dwmw2@infradead.org>, Wei Liu <wei.liu2@citrix.com>, Alex Williamson <alex.williamson@redhat.com>, peterx@redhat.com, Stefan Hajnoczi <stefanha@redhat.com>, Linux Virtualization <virtualization@lists.linux-foundation.org>, qemu-block@nongnu.org, Kevin Wolf <kwolf@redhat.com>, Amit Shah <amit.shah@redhat.com>, "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>, Jason Wang <jasowang@redhat.com>, Paolo Bonzini <pbonzini@redhat.com>, kvm list <kvm@vger.kernel.org>

On Tue, Apr 19, 2016 at 09:00:27AM -0700, Andy Lutomirski wrote:
> On Apr 19, 2016 2:13 AM, "Michael S. Tsirkin" <mst@redhat.com> wrote:
> >
> >
> > I guess you are right in that we should split this part out.
> > What I wanted is really the combination
> > PASSTHROUGH && !PLATFORM so that we can say "ok we don't
> > need to guess, this device actually bypasses the IOMMU".
> 
> What happens when you use a device like this on Xen or with a similar
> software translation layer?

I think you don't use it on Xen since virtio doesn't bypass an IOMMU there.
If you do you have misconfigured your device.

-- 
MST