Re: [PATCH] virtio-net: clear guest_announce feature if no cvq backend

[Lei Yang]

QE uses the sim_vdpa device to test this patch and add "ctrl_vq=off"
in the qemu command line. Guest can find this device, there are no any
error messages in guest dmesg, and can migrate successfully.

Tested-by: Lei Yang <leiyang@redhat.com>

Eugenio Perez Martin <eperezma@redhat.com> 于2023年2月14日周二 14:53写道：
>
> On Tue, Jan 24, 2023 at 5:32 PM Eugenio Pérez <eperezma@redhat.com> wrote:
> >
> > Since GUEST_ANNOUNCE is emulated the feature bit could be set without
> > backend support.  This happens in the vDPA case.
> >
> > However, backend vDPA parent may not have CVQ support.  This causes an
> > incoherent feature set, and the driver may refuse to start.  This
> > happens in virtio-net Linux driver.
> >
> > This may be solved differently in the future.  Qemu is able to emulate a
> > CVQ just for guest_announce purposes, helping guest to notify the new
> > location with vDPA devices that does not support it.  However, this is
> > left as a TODO as it is way more complex to backport.
> >
> > Tested with vdpa_net_sim, toggling manually VIRTIO_NET_F_CTRL_VQ in the
> > driver and migrating it with x-svq=on.
> >
>
> Friendly ping about this patch, as it fell through the cracks if I'm not 
> wrong.
>
> Thanks!
>
> > Fixes: 980003debddd ("vdpa: do not handle VIRTIO_NET_F_GUEST_ANNOUNCE in 
> > vhost-vdpa")
> > Reported-by: Dawar, Gautam <gautam.dawar@amd.com>
> > Signed-off-by: Eugenio Pérez <eperezma@redhat.com>
> > ---
> >  hw/net/virtio-net.c | 15 +++++++++++++++
> >  1 file changed, 15 insertions(+)
> >
> > diff --git a/hw/net/virtio-net.c b/hw/net/virtio-net.c
> > index 3ae909041a..09d5c7a664 100644
> > --- a/hw/net/virtio-net.c
> > +++ b/hw/net/virtio-net.c
> > @@ -820,6 +820,21 @@ static uint64_t virtio_net_get_features(VirtIODevice 
> > *vdev, uint64_t features,
> >          features |= (1ULL << VIRTIO_NET_F_MTU);
> >      }
> >
> > +    /*
> > +     * Since GUEST_ANNOUNCE is emulated the feature bit could be set 
> > without
> > +     * enabled. This happens in the vDPA case.
> > +     *
> > +     * Make sure the feature set is not incoherent, as the driver could 
> > refuse
> > +     * to start.
> > +     *
> > +     * TODO: QEMU is able to emulate a CVQ just for guest_announce 
> > purposes,
> > +     * helping guest to notify the new location with vDPA devices that 
> > does not
> > +     * support it.
> > +     */
> > +    if (!virtio_has_feature(vdev->backend_features, VIRTIO_NET_F_CTRL_VQ)) 
> > {
> > +        virtio_clear_feature(&features, VIRTIO_NET_F_GUEST_ANNOUNCE);
> > +    }
> > +
> >      return features;
> >  }
> >
> > --
> > 2.31.1
> >
> >
>