Re: [PATCH 09/31] vhost-vdpa: Take into account SVQ in vhost_vdpa_set_vring_call

[Eugenio Perez Martin]

On Sat, Jan 29, 2022 at 9:06 AM Jason Wang <jasowang@redhat.com> wrote:
>
>
> 在 2022/1/22 上午4:27, Eugenio Pérez 写道:
> > Signed-off-by: Eugenio Pérez <eperezma@redhat.com>
> > ---
> >   hw/virtio/vhost-vdpa.c | 20 ++++++++++++++++++--
> >   1 file changed, 18 insertions(+), 2 deletions(-)
> >
> > diff --git a/hw/virtio/vhost-vdpa.c b/hw/virtio/vhost-vdpa.c
> > index 18de14f0fb..029f98feee 100644
> > --- a/hw/virtio/vhost-vdpa.c
> > +++ b/hw/virtio/vhost-vdpa.c
> > @@ -687,13 +687,29 @@ static int vhost_vdpa_set_vring_kick(struct vhost_dev 
> > *dev,
> >       }
> >   }
> >
> > -static int vhost_vdpa_set_vring_call(struct vhost_dev *dev,
> > -                                       struct vhost_vring_file *file)
> > +static int vhost_vdpa_set_vring_dev_call(struct vhost_dev *dev,
> > +                                         struct vhost_vring_file *file)
> >   {
> >       trace_vhost_vdpa_set_vring_call(dev, file->index, file->fd);
> >       return vhost_vdpa_call(dev, VHOST_SET_VRING_CALL, file);
> >   }
> >
> > +static int vhost_vdpa_set_vring_call(struct vhost_dev *dev,
> > +                                     struct vhost_vring_file *file)
> > +{
> > +    struct vhost_vdpa *v = dev->opaque;
> > +
> > +    if (v->shadow_vqs_enabled) {
> > +        int vdpa_idx = vhost_vdpa_get_vq_index(dev, file->index);
> > +        VhostShadowVirtqueue *svq = g_ptr_array_index(v->shadow_vqs, 
> > vdpa_idx);
> > +
> > +        vhost_svq_set_guest_call_notifier(svq, file->fd);
>
>
> Two questions here (had similar questions for vring kick):
>
> 1) Any reason that we setup the eventfd for vhost-vdpa in
> vhost_vdpa_svq_setup() not here?
>

I'm not sure what you mean.

The guest->SVQ call and kick fds are set here and at
vhost_vdpa_set_vring_kick. The event notifier handler of the guest ->
SVQ kick_fd is set at vhost_vdpa_set_vring_kick /
vhost_svq_set_svq_kick_fd. The guest -> SVQ call fd has no event
notifier handler since we don't poll it.

On the other hand, the connection SVQ <-> device uses the same fds
from the beginning to the end, and they will not change with, for
example, call fd masking. That's why it's setup from
vhost_vdpa_svq_setup. Delaying to vhost_vdpa_set_vring_call would make
us add way more logic there.

> 2) The call could be disabled by using -1 as the fd, I don't see any
> code to deal with that.
>

Right, I didn't take that into account. vhost-kernel takes also -1 as
kick_fd to unbind, so SVQ can be reworked to take that into account
for sure.

Thanks!

> Thanks
>
>
> > +        return 0;
> > +    } else {
> > +        return vhost_vdpa_set_vring_dev_call(dev, file);
> > +    }
> > +}
> > +
> >   /**
> >    * Set shadow virtqueue descriptors to the device
> >    *
>