Re: virtio-iommu issue with VFIO device downstream to a PCIe-to-PCI bridge: VFIO devices are not assigned any iommu group

[Jean-Philippe Brucker <jean-philippe@linaro.org>]

Hi,

On Mon, Jan 09, 2023 at 10:11:19PM +0100, Eric Auger wrote:
> > Jean, do you have any idea about how to fix that? Do you think we have a
> > trouble in the acpi/viot setup or virtio-iommu probe sequence. It looks
> > like virtio probe and attach commands are called too early, before the
> > bus is actually correctly numbered.
> 
> So after further investigations looks this is not a problem of bus
> number, which is good at the time of the virtio cmd calls but rather a
> problem related to the devfn (0 was used when creating the IOMMU MR)
> whereas the virtio-iommu cmds looks for the non aliased devfn. With that
> fixed, the probe and attach at least succeeds. The device still does not
> work for me but I will continue my investigations and send a tentative fix.

If I remember correctly VIOT can deal with bus numbers because bridges are
assigned a range by QEMU, but I haven't tested that in detail, and I don't
know how it holds with conventional PCI bridges. Do you have an example
command-line I could use to experiment (and the fix you're mentioning)?

Thanks,
Jean