Re: [virtio-dev] [RFC PATCH v2 4/5] ACPI/IORT: Support paravirtualized IOMMU

[Jean-Philippe Brucker <jean-philippe.brucker@arm.com>]

On 17/11/17 18:52, Jean-Philippe Brucker wrote:
> To describe the virtual topology in relation to a virtio-iommu device,
> ACPI-based systems use a "paravirtualized IOMMU" IORT node. Add support
> for it.
> 
> This is a RFC because the IORT specification doesn't describe the
> paravirtualized node at the moment, it is only provided as an example in
> the virtio-iommu spec. What we need to do first is confirm that x86
> kernels are able to use the IORT driver with the virtio-iommu. There isn't
> anything specific to arm64 in the driver but there might be other blockers
> we're not aware of (I know for example that x86 also requires custom DMA
> ops rather than iommu-dma ones, but it's unrelated) so this needs to be
> tested on the x86 prototype.

I tested IORT with an x86 guest, putting a virtio-iommu on the PCI bus and
it worked fine :)

x86 still requires additional code [1] for using the IOMMU DMA ops,
and I'm not comfortable enough with x86 to write the patch, but for
instantiating virtio-iommus and for enumerating endpoints/buses connected
to them, IORT should suffice.

Thanks,
Jean

[1]
http://www.linux-arm.org/git?p=linux-jpb.git;a=patch;h=e910e224b58712151dda06df595a53ff07edef63;hp=e7f9475480c24c5f973711984b30cf6746ff3ec8