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

["Michael S. Tsirkin" <mst@redhat.com>]

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.


> 
> >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):

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 =