Re: [PATCH v12 03/13] vfio: VFIO_IOMMU_SET_MSI_BINDING

[Jean-Philippe Brucker]

Hi,

On Tue, Feb 23, 2021 at 10:06:15PM +0100, Eric Auger wrote:
> This patch adds the VFIO_IOMMU_SET_MSI_BINDING ioctl which aim
> to (un)register the guest MSI binding to the host. This latter
> then can use those stage 1 bindings to build a nested stage
> binding targeting the physical MSIs.

Now that RMR is in the IORT spec, could it be used for the nested MSI
problem?  For virtio-iommu tables I was planning to do it like this:

MSI is mapped at stage-2 with an arbitrary IPA->doorbell PA. We report
this IPA to userspace through iommu_groups/X/reserved_regions. No change
there. Then to the guest we report a reserved identity mapping at IPA
(using RMR, an equivalent DT binding, or probed RESV_MEM for
virtio-iommu). The guest creates that mapping at stage-1, and that's it.
Unless I overlooked something we'd only reuse existing infrastructure and
avoid the SET_MSI_BINDING interface.

Thanks,
Jean