Re: [PATCH 1/2] vdpa_sim: not reset state in vdpasim_queue_ready

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

On Thu, Jan 19, 2023 at 4:16 AM Jason Wang <jasowang@redhat.com> wrote:
>
> On Thu, Jan 19, 2023 at 12:44 AM Eugenio Pérez <eperezma@redhat.com> wrote:
> >
> > vdpasim_queue_ready calls vringh_init_iotlb, which resets split indexes.
> > But it can be called after setting a ring base with
> > vdpasim_set_vq_state.
> >
> > Fix it by stashing them. They're still resetted in vdpasim_vq_reset.
> >
> > This was discovered and tested live migrating the vdpa_sim_net device.
> >
> > Fixes: 2c53d0f64c06 ("vdpasim: vDPA device simulator")
> > Signed-off-by: Eugenio Pérez <eperezma@redhat.com>
> > ---
> >  drivers/vdpa/vdpa_sim/vdpa_sim.c | 2 ++
> >  1 file changed, 2 insertions(+)
> >
> > diff --git a/drivers/vdpa/vdpa_sim/vdpa_sim.c b/drivers/vdpa/vdpa_sim/vdpa_sim.c
> > index cb88891b44a8..8839232a3fcb 100644
> > --- a/drivers/vdpa/vdpa_sim/vdpa_sim.c
> > +++ b/drivers/vdpa/vdpa_sim/vdpa_sim.c
> > @@ -66,6 +66,7 @@ static void vdpasim_vq_notify(struct vringh *vring)
> >  static void vdpasim_queue_ready(struct vdpasim *vdpasim, unsigned int idx)
> >  {
> >         struct vdpasim_virtqueue *vq = &vdpasim->vqs[idx];
> > +       uint16_t last_avail_idx = vq->vring.last_avail_idx;
> >
> >         vringh_init_iotlb(&vq->vring, vdpasim->features, vq->num, false,
> >                           (struct vring_desc *)(uintptr_t)vq->desc_addr,
> > @@ -74,6 +75,7 @@ static void vdpasim_queue_ready(struct vdpasim *vdpasim, unsigned int idx)
> >                           (struct vring_used *)
> >                           (uintptr_t)vq->device_addr);
> >
> > +       vq->vring.last_avail_idx = last_avail_idx;
>
> Does this need to be serialized with the datapath?
>
> E.g in set_vq_state() we do:
>
> spin_lock(&vdpasim->lock);
> vrh->last_avail_idx = state->split.avail_index;
> spin_unlock(&vdpasim->lock);
>

vdpasim_queue_ready is called from vdpasim_set_vq_ready, which holds
these locks.

Maybe it's too much indirection and to embed vdpasim_queue_ready in
vdpasim_set_vq_ready would be clearer for the future?

Thanks!