Re: [PATCH v6 0/7] Add virtio-iommu driver

["Michael S. Tsirkin" <mst@redhat.com>]

On Wed, Dec 12, 2018 at 11:35:45AM +0100, Joerg Roedel wrote:
> Hi,
> 
> to make progress on this, we should first agree on the protocol used
> between guest and host. I have a few points to discuss on the protocol
> first.
> 
> On Tue, Dec 11, 2018 at 06:20:57PM +0000, Jean-Philippe Brucker wrote:
> > [1] Virtio-iommu specification v0.9, sources and pdf
> >     git://linux-arm.org/virtio-iommu.git virtio-iommu/v0.9
> >     http://jpbrucker.net/virtio-iommu/spec/v0.9/virtio-iommu-v0.9.pdf
> 
> Looking at this I wonder why it doesn't make the IOTLB visible to the
> guest. the UNMAP requests seem to require that the TLB is already
> flushed to make the unmap visible.
> 
> I think that will cost significant performance for both, vfio and
> dma-iommu use-cases which both do (vfio at least to some degree),
> deferred flushing.
> 
> I also wonder whether the protocol should implement a
> protocol version handshake

virtio has a builtin version handshake so devices don't need to.

> and iommu-feature set queries.
> 
> > [3] git://linux-arm.org/linux-jpb.git virtio-iommu/v0.9.1
> >     git://linux-arm.org/kvmtool-jpb.git virtio-iommu/v0.9
> 
> Unfortunatly gitweb seems to be broken on linux-arm.org. What is missing
> in this patch-set to make this work on x86?

And I wonder about pcc too.

> Regards,
> 
> 	Joerg