Re: [RFC PATCH v8 12/21] vdpa: delay set_vring_ready after DRIVER_OK

[Eugenio Perez Martin <eperezma@redhat.com>]

On Wed, Jun 8, 2022 at 6:21 AM Jason Wang <jasowang@redhat.com> wrote:
>
>
> 在 2022/5/20 03:12, Eugenio Pérez 写道:
> > To restore the device in the destination of a live migration we send the
> > commands through control virtqueue. For a device to read CVQ it must
> > have received DRIVER_OK status bit.
> >
> > However this open a window where the device could start receiving
> > packets in rx queue 0 before it receive the RSS configuration. To avoid
> > that, we will not send vring_enable until all configuration is used by
> > the device.
> >
> > As a first step, reverse the DRIVER_OK and SET_VRING_ENABLE steps.
> >
> > Signed-off-by: Eugenio Pérez <eperezma@redhat.com>
>
>
> I may miss something, but it looks to me this should be an independent
> patch or it should depend on live migration series.
>

With x-svq it's possible to migrate a VM, because we don't need to
stop the device: VMM always knows the vq state to program in the
destination (assuming no need for inflight etc).

But it will have better context in the next series for sure.

Thanks!

> Thanks
>
>
> > ---
> >   hw/virtio/vhost-vdpa.c | 20 +++++++++++++++-----
> >   1 file changed, 15 insertions(+), 5 deletions(-)
> >
> > diff --git a/hw/virtio/vhost-vdpa.c b/hw/virtio/vhost-vdpa.c
> > index 31b3d4d013..13e5e2a061 100644
> > --- a/hw/virtio/vhost-vdpa.c
> > +++ b/hw/virtio/vhost-vdpa.c
> > @@ -748,13 +748,18 @@ static int vhost_vdpa_get_vq_index(struct vhost_dev *dev, int idx)
> >       return idx;
> >   }
> >
> > +/**
> > + * Set ready all vring of the device
> > + *
> > + * @dev: Vhost device
> > + */
> >   static int vhost_vdpa_set_vring_ready(struct vhost_dev *dev)
> >   {
> >       int i;
> >       trace_vhost_vdpa_set_vring_ready(dev);
> > -    for (i = 0; i < dev->nvqs; ++i) {
> > +    for (i = 0; i < dev->vq_index_end; ++i) {
> >           struct vhost_vring_state state = {
> > -            .index = dev->vq_index + i,
> > +            .index = i,
> >               .num = 1,
> >           };
> >           vhost_vdpa_call(dev, VHOST_VDPA_SET_VRING_ENABLE, &state);
> > @@ -1117,7 +1122,6 @@ static int vhost_vdpa_dev_start(struct vhost_dev *dev, bool started)
> >           if (unlikely(!ok)) {
> >               return -1;
> >           }
> > -        vhost_vdpa_set_vring_ready(dev);
> >       } else {
> >           ok = vhost_vdpa_svqs_stop(dev);
> >           if (unlikely(!ok)) {
> > @@ -1131,16 +1135,22 @@ static int vhost_vdpa_dev_start(struct vhost_dev *dev, bool started)
> >       }
> >
> >       if (started) {
> > +        int r;
> >           memory_listener_register(&v->listener, &address_space_memory);
> > -        return vhost_vdpa_add_status(dev, VIRTIO_CONFIG_S_DRIVER_OK);
> > +        r = vhost_vdpa_add_status(dev, VIRTIO_CONFIG_S_DRIVER_OK);
> > +        if (unlikely(r)) {
> > +            return r;
> > +        }
> > +        vhost_vdpa_set_vring_ready(dev);
> >       } else {
> >           vhost_vdpa_reset_device(dev);
> >           vhost_vdpa_add_status(dev, VIRTIO_CONFIG_S_ACKNOWLEDGE |
> >                                      VIRTIO_CONFIG_S_DRIVER);
> >           memory_listener_unregister(&v->listener);
> >
> > -        return 0;
> >       }
> > +
> > +    return 0;
> >   }
> >
> >   static int vhost_vdpa_set_log_base(struct vhost_dev *dev, uint64_t base,
>