Hi Peng,
We haven't tried to setup virtio-vsock yet.
In general, I am very supportive of using QEMU for virtio backends. We
use QEMU to provide virtio-net, virtio-block, virtio-console and more.
However, typically virtio-vsock comes into play for VM-to-VM
communication, which is different. Going via QEMU in Dom0 just to have 1
VM communicate with another VM is not an ideal design: it adds latency
and uses resources in Dom0 when actually we could do without it.
A better model for VM-to-VM communication would be to have the VM talk
to each other directly via grant table or pre-shared memory (see the
static shared memory feature) or via Xen hypercalls (see Argo.)
For a good Xen design, I think the virtio-vsock backend would need to be
in Xen itself (the hypervisor).
Of course that is more work and it doesn't help you with the specific
question you had below :-)
For that, I don't have a pointer to help you but maybe others in CC
have.
Cheers,
Stefano
On Fri, 23 Feb 2024, Peng Fan wrote:
> Hi All,
>
> Has anyone make virtio-vsock on xen work? My dm args as below:
>
> virtio = [
> 'backend=0,type=virtio,device,transport=pci,bdf=05:00.0,backend_type=qemu,grant_usage=true'
> ]
> device_model_args = [
> '-D', '/home/root/qemu_log.txt',
> '-d',
> 'trace:*vsock*,trace:*vhost*,trace:*virtio*,trace:*pci_update*,trace:*pci_route*,trace:*handle_ioreq*,trace:*xen*',
> '-device',
> 'vhost-vsock-pci,iommu_platform=false,id=vhost-vsock-pci0,bus=pcie.0,addr=5.0,guest-cid=3']
>
> During my test, it always return failure in dom0 kernel in below code:
>
> vhost_transport_do_send_pkt {
> ...
> nbytes = copy_to_iter(hdr, sizeof(*hdr), &iov_iter);
>
> if (nbytes != sizeof(*hdr)) {
>
> vq_err(vq, "Faulted on copying pkt hdr %x %x %x
> %px\n", nbytes, sizeof(*hdr),
> __builtin_object_size(hdr, 0), &iov_iter);
> kfree_skb(skb);
>
> break;
>
> }
> }
>
> I checked copy_to_iter, it is copy data to __user addr, but it never pass,
> the copy to __user addr always return 0 bytes copied.
>
> The asm code "sttr x7, [x6]" will trigger data abort, the kernel will run
> into do_page_fault, but lock_mm_and_find_vma report it is VM_FAULT_BADMAP,
> that means the __user addr is not mapped, no vma has this addr.
>
> I am not sure what may cause this. Appreciate if any comments.
>
> BTW: I tested blk pci, it works, so the virtio pci should work on my setup.
>
> Thanks,
> Peng.
>
