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

[Joerg Roedel <joro@8bytes.org>]

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 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?

Regards,

	Joerg