[vfio-users] Nested VFIO with QEMU

[Boeuf, Sebastien]

Hi folks,

I have been recently working with VFIO, and particularly trying to
achieve device passthrough through multiple layers of virtualization.

I wanted to assess QEMU's performances with nested VFIO, using the
emulated Intel IOMMU device. Unfortunately, I cannot make any of my
physical device work when I pass them through, attached to the emulated
Intel IOMMU. Using regular VFIO works properly, but as soon as I enable
the virtual IOMMU, the driver fails to probe (I tried on two different
machines with different types of NIC).

So I was wondering if someone was aware of any issue with using both
VFIO and virtual Intel IOMMU with QEMU? I'm sure I might be missing
something obvious but I couldn't find it so far.

Thanks,
Sebastien