Re: [PATCH v16 00/10] VIRTIO-IOMMU device

[Zhangfei Gao]

Hi Eric

On Thu, Feb 27, 2020 at 9:50 PM Auger Eric <address@hidden> wrote:
>
> Hi Daniel,
>
> On 2/27/20 12:17 PM, Daniel P. Berrangé wrote:
> > On Fri, Feb 14, 2020 at 02:27:35PM +0100, Eric Auger wrote:
> >> This series implements the QEMU virtio-iommu device.
> >>
> >> This matches the v0.12 spec (voted) and the corresponding
> >> virtio-iommu driver upstreamed in 5.3. All kernel dependencies
> >> are resolved for DT integration. The virtio-iommu can be
> >> instantiated in ARM virt using:
> >>
> >> "-device virtio-iommu-pci".
> >
> > Is there any more documentation besides this ?
>
> not yet in qemu.
> >
> > I'm wondering on the intended usage of this, and its relation
> > or pros/cons vs other iommu devices
>
> Maybe if you want to catch up on the topic, looking at the very first
> kernel RFC may be a good starting point. Motivation, pros & cons were
> discussed in that thread (hey, April 2017!)
> https://lists.linuxfoundation.org/pipermail/iommu/2017-April/021217.html
>
> on ARM we have SMMUv3 emulation. But the VFIO integration is not
> possible because SMMU does not have any "caching mode" and my nested
> paging kernel series is blocked. So the only solution to integrate with
> VFIO is looming virtio-iommu.
>
> In general the pros that were put forward are: virtio-iommu is
> architecture agnostic, removes the burden to accurately model complex
> device states, driver can support virtualization specific optimizations
> without being constrained by production driver maintenance. Cons is perf
> and mem footprint if we do not consider any optimization.
>
> You can have a look at
>
> http://events17.linuxfoundation.org/sites/events/files/slides/viommu_arm.pdf
>
Thanks for the patches.

Could I ask one question?
To support vSVA and pasid in guest, which direction you recommend,
virtio-iommu or vSMMU (your nested paging)

Do we still have any obstacles?
Would you mind give some breakdown.
Jean mentioned PASID still not supported in QEMU.

Thanks