vIOMMU - PCI pass through to Layer 2 VMs (Nested Virtualization)

[Markus Frank]

Hello,

I have already sent this email to qemu-discuss but I did not get a reply.
https://lists.nongnu.org/archive/html/qemu-discuss/2023-09/msg00034.html
Maybe someone here could help me and reply to this email or the one on 
qemu-discuss?

I would like to pass through PCI devices to Layer-2 VMs via Nested 
Virtualization.

Is there current documentation for this topic somewhere?

I used these parameters:
-machine ...,kernel-irqchip=split
-device intel-iommu

With these parameters PCI pass through to L2-VMs worked fine.


Now I come to the part where I get confused.

https://wiki.qemu.org/Features/VT-d#With_Virtio_Devices
Is this documentation relevant for PCI pass through? Do I need DMAR for virtio 
devices?

And there is also the virtio-iommu device where I also could use the i440fx 
chipset.
https://michael2012z.medium.com/virtio-iommu-789369049443

When adding "-device virtio-iommu-pci" pci pass through also works
but I get "kvm: virtio_iommu_translate no mapping for 0x1002030f000 for sid=240"
when starting qemu. What could that mean?

What do these parameters 
"disable-legacy=on,disable-modern=off,iommu_platform=on,ats=on"
actually do? When do I need them and on which virtio devices?

And which device should I rather use: virtio-iommu or intel-iommu?

Thanks in advance,
Markus