Re: [PATCH v2 3/4] vdpa: handle VIRTIO_NET_CTRL_ANNOUNCE in vhost_vdpa_net_handle_ctrl_avail

[Jason Wang]

On Wed, Nov 30, 2022 at 3:07 PM Eugenio Perez Martin
<eperezma@redhat.com> wrote:
>
> On Wed, Nov 30, 2022 at 8:02 AM Jason Wang <jasowang@redhat.com> wrote:
> >
> > On Fri, Nov 25, 2022 at 1:33 AM Eugenio Pérez <eperezma@redhat.com> wrote:
> > >
> > > Since this capability is emulated by qemu shadowed CVQ cannot forward it
> > > to the device. Process all that command within qemu.
> > >
> > > Signed-off-by: Eugenio Pérez <eperezma@redhat.com>
> > > ---
> > >  net/vhost-vdpa.c | 15 ++++++++++++---
> > >  1 file changed, 12 insertions(+), 3 deletions(-)
> > >
> > > diff --git a/net/vhost-vdpa.c b/net/vhost-vdpa.c
> > > index 2b4b85d8f8..8172aa8449 100644
> > > --- a/net/vhost-vdpa.c
> > > +++ b/net/vhost-vdpa.c
> > > @@ -489,9 +489,18 @@ static int 
> > > vhost_vdpa_net_handle_ctrl_avail(VhostShadowVirtqueue *svq,
> > >      out.iov_len = iov_to_buf(elem->out_sg, elem->out_num, 0,
> > >                               s->cvq_cmd_out_buffer,
> > >                               vhost_vdpa_net_cvq_cmd_len());
> > > -    dev_written = vhost_vdpa_net_cvq_add(s, out.iov_len, sizeof(status));
> > > -    if (unlikely(dev_written < 0)) {
> > > -        goto out;
> > > +    if (*(uint8_t *)s->cvq_cmd_out_buffer == VIRTIO_NET_CTRL_ANNOUNCE) {
> > > +        /*
> > > +         * Guest announce capability is emulated by qemu, so dont 
> > > forward to
> >
> > s/dont/don't/
> >
>
> I'll correct it, thanks!
>
> > > +         * the device.
> > > +         */
> > > +        dev_written = sizeof(status);
> > > +        *s->status = VIRTIO_NET_OK;
> >
> > I wonder if we should avoid negotiating ANNOUNCE with vDPA parents if
> > we do this?
> >
>
> I can re-check, but the next patch should avoid it.

Kind of, it makes sure guest can always see _F_ANNOUNCE. But does it
prevent _F_ANNOUNCE from being negotiated?

> Even if
> negotiated, the parent should never set the announce status bit, since
> we never tell the device is a destination device.

That's the point, do we have such a guarantee? Or I wonder if there's
any parent that supports _F_ANNOUNCE if yes, how it is supposed to
work?

>
> But it's better to be on the safe side, I'll recheck.

Exactly.

Thanks

>
> Thanks!
>
> > Thanks
> >
> > > +    } else {
> > > +        dev_written = vhost_vdpa_net_cvq_add(s, out.iov_len, 
> > > sizeof(status));
> > > +        if (unlikely(dev_written < 0)) {
> > > +            goto out;
> > > +        }
> > >      }
> > >
> > >      if (unlikely(dev_written < sizeof(status))) {
> > > --
> > > 2.31.1
> > >
> >
>