Hi, On 10/9/23 12:25, Markus Frank wrote: > Hi Eric, > > thanks for the quick answer. > > On 10/9/23 11:29, Eric Auger wrote: >> 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 device>> >>> 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. > Yes I know. I meant that intel-iommu does not support i440fx and > virtio-iommu does.
>>> >>> 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? > Yes. I didn't notice any problems. How could I find out what the > requester id 0x240 refers to? on your guest issue lspci and look at the end points BDF that matches 0x240. >>> >>> 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. > Okay, so iommu_platform=on is more of a decision you should make per > virtio-pci device. > So simplified the advantage is more isolation and the disadvantage is > less performance? yes setting iommu_platform forces the driver to use the DMA API. Eric >>> >>> 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 >>> >>> >> >> >
