Hi Markus, On 10/9/23 09:06, Markus Frank wrote: > 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? If you just want the host assigned devices to be protected by the viommu, you don't need to add iommu_platform=on along with the virtio-pci devices. > > And there is also the virtio-iommu device where I also could use the > i440fx chipset. > https://michael2012z.medium.com/virtio-iommu-789369049443
you can use virtio-iommu with q35 machine. > > 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? Normally you shouldn't get any such error. This means there is no mapping programmed by the iommu-driver for this requester id (0x240) and this iova=0x1002030f000. But if I understand correctly this does not prevent your device from working, correct? > > 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? you need them if you want your virtio devices to be protected by the viommu. Otherwise the viommu is bypassed. > > And which device should I rather use: virtio-iommu or intel-iommu? Both should be working. virtio-iommu is more recent and less used in production than intel-iommu though. Thanks Eric > > Thanks in advance, > Markus > >
