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Message-ID: <20160427180610-mutt-send-email-mst@redhat.com>
Date: Wed, 27 Apr 2016 18:09:31 +0300
From: "Michael S. Tsirkin" <mst@...hat.com>
To: Joerg Roedel <joro@...tes.org>
Cc: Andy Lutomirski <luto@...capital.net>,
David Woodhouse <dwmw2@...radead.org>,
Kevin Wolf <kwolf@...hat.com>, Wei Liu <wei.liu2@...rix.com>,
Andy Lutomirski <luto@...nel.org>, qemu-block@...gnu.org,
Christian Borntraeger <borntraeger@...ibm.com>,
Jason Wang <jasowang@...hat.com>,
Stefano Stabellini <stefano.stabellini@...citrix.com>,
"qemu-devel@...gnu.org Developers" <qemu-devel@...gnu.org>,
peterx@...hat.com,
"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
Amit Shah <amit.shah@...hat.com>,
iommu@...ts.linux-foundation.org,
Stefan Hajnoczi <stefanha@...hat.com>,
kvm list <kvm@...r.kernel.org>,
Cornelia Huck <cornelia.huck@...ibm.com>,
Paolo Bonzini <pbonzini@...hat.com>,
Linux Virtualization <virtualization@...ts.linux-foundation.org>,
Anthony PERARD <anthony.perard@...rix.com>
Subject: Re: [PATCH V2 RFC] fixup! virtio: convert to use DMA api
On Wed, Apr 27, 2016 at 04:58:51PM +0200, Joerg Roedel wrote:
> On Wed, Apr 27, 2016 at 05:54:57PM +0300, Michael S. Tsirkin wrote:
> > Point is, QEMU is not the only virtio implementation out there.
> > So we can't know no virtio implementations have an IOMMU as long as
> > linux supports this IOMMU.
> > virtio always used physical addresses since it was born and if it
> > changes that it must do this in a way that does not break existing
> > users.
>
> FWIW, virtio in qemu can continue to just use physical addresses. But
> qemu needs to advertise that fact correctly to the OS in the DMAR table.
> This way old kernels (where virtio does not use DMA-API) will also
> continue to work on the fixed qemu.
>
>
>
> Joerg
It's not clear it can do this since DMAR tables seem to assume
a given slot is either bypassing IOMMU or going through it.
QEMU allows reusing same slot for virtio and non-virtio devices.
Besides, this patch is not about it, it's a flag for QEMU to
tell guest that it can trust DMAR tables.
--
MST
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