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?
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?
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
