Re: [Qemu-devel] QEMU -netdev vhost=on + -device virtio-net-pci bug

[Alexey Kardashevskiy <aik@ozlabs.ru>]

On 06/03/13 01:23, Michael S. Tsirkin wrote:
> On Wed, Mar 06, 2013 at 12:21:47AM +1100, Alexey Kardashevskiy wrote:
>> On 05/03/13 23:56, Michael S. Tsirkin wrote:
>>>> The patch f56a12475ff1b8aa61210d08522c3c8aaf0e2648 "vhost: backend
>>>> masking support" breaks virtio-net + vhost=on on PPC64 platform.
>>>>
>>>> The problem command line is:
>>>> 1) -netdev tap,id=tapnet,ifname=tap0,script=qemu-ifup.sh,vhost=on \
>>>> -device virtio-net-pci,netdev=tapnet,addr=0.0 \
>>>
>>> I think the issue is irqfd in not supported on kvm ppc.
>>
>> How can I make sure this is the case? Some work has been done there
>> recently but midnight is quite late to figure this out :)
>
> Look in virtio_pci_set_guest_notifiers, what is the
> value of with_irqfd?
>    bool with_irqfd = msix_enabled(&proxy->pci_dev) &&
>          kvm_msi_via_irqfd_enabled();
>
> Also check what each of the values in the expression above is.

Yes, ppc does not have irqfd as kvm_msi_via_irqfd_enabled() returned "false".

>>> Could you please check this:
>>>
>>> +        /* If guest supports masking, set up irqfd now.
>>> +         * Otherwise, delay until unmasked in the frontend.
>>> +         */
>>> +        if (proxy->vdev->guest_notifier_mask) {
>>> +            ret = kvm_virtio_pci_irqfd_use(proxy, queue_no, vector);
>>> +            if (ret < 0) {
>>> +                kvm_virtio_pci_vq_vector_release(proxy, vector);
>>> +                goto undo;
>>> +            }
>>> +        }
>>>
>>>
>>> Could you please add a printf before "undo" and check whether the
>>> error path above is triggered?
>>
>>
>> Checked, it is not triggered.
>>
>>
>> --
>> Alexey
>
> I think I get it.
> Does the following help (probably not the right thing to do, but just
> for testing):


It did not compile (no "queue_no") :) I changed it a bit and now vhost=on 
works fine:

diff --git a/hw/virtio-pci.c b/hw/virtio-pci.c
index a869f53..df1e443 100644
--- a/hw/virtio-pci.c
+++ b/hw/virtio-pci.c
@@ -798,6 +798,10 @@ static int virtio_pci_set_guest_notifiers(DeviceState 
*d, int nvqs, bool assign)
          if (r < 0) {
              goto assign_error;
          }
+
+        if (!with_irqfd && proxy->vdev->guest_notifier_mask) {
+            proxy->vdev->guest_notifier_mask(proxy->vdev, n, !assign);
+        }
      }

      /* Must set vector notifier after guest notifier has been assigned */




> Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
>
> ---
>
> diff --git a/hw/virtio-pci.c b/hw/virtio-pci.c
> index ba56ab2..c2a0c5a 100644
> --- a/hw/virtio-pci.c
> +++ b/hw/virtio-pci.c
> @@ -800,6 +800,10 @@ static int virtio_pci_set_guest_notifiers(DeviceState *d, int nvqs, bool assign)
>           }
>       }
>
> +    if (!with_irqfd && proxy->vdev->guest_notifier_mask) {
> +        proxy->vdev->guest_notifier_mask(proxy->vdev, queue_no, !assign);
> +    }
> +
>       /* Must set vector notifier after guest notifier has been assigned */
>       if (with_irqfd && assign) {
>           proxy->vector_irqfd =
>


-- 
Alexey