Subject: Re: [PATCH] vdpa/mlx5: should keep avail_index despite device status

From: "Michael S. Tsirkin" <[email-masked]>
Date: Tue, 6 Oct 2020 02:22:15 -0400

On Fri, Oct 02, 2020 at 01:17:00PM -0700, Si-Wei Liu wrote:
> + Eli.
> 
> On Thu, Oct 1, 2020 at 2:02 PM Si-Wei Liu <[email-masked]> wrote:
> >
> > A VM with mlx5 vDPA has below warnings while being reset:
> >
> > vhost VQ 0 ring restore failed: -1: Resource temporarily unavailable (11)
> > vhost VQ 1 ring restore failed: -1: Resource temporarily unavailable (11)
> >
> > We should allow userspace emulating the virtio device be
> > able to get to vq's avail_index, regardless of vDPA device
> > status. Save the index that was last seen when virtq was
> > stopped, so that userspace doesn't complain.
> >
> > Signed-off-by: Si-Wei Liu <[email-masked]>

Eli can you review this pls? I need to send a pull request to Linux by
tomorrow - do we want to include this?

> > ---
> >  drivers/vdpa/mlx5/net/mlx5_vnet.c | 20 ++++++++++++++------
> >  1 file changed, 14 insertions(+), 6 deletions(-)
> >
> > diff --git a/drivers/vdpa/mlx5/net/mlx5_vnet.c b/drivers/vdpa/mlx5/net/mlx5_vnet.c
> > index 70676a6..74264e59 100644
> > --- a/drivers/vdpa/mlx5/net/mlx5_vnet.c
> > +++ b/drivers/vdpa/mlx5/net/mlx5_vnet.c
> > @@ -1133,15 +1133,17 @@ static void suspend_vq(struct mlx5_vdpa_net *ndev, struct mlx5_vdpa_virtqueue *m
> >         if (!mvq->initialized)
> >                 return;
> >
> > -       if (query_virtqueue(ndev, mvq, &attr)) {
> > -               mlx5_vdpa_warn(&ndev->mvdev, "failed to query virtqueue\n");
> > -               return;
> > -       }
> >         if (mvq->fw_state != MLX5_VIRTIO_NET_Q_OBJECT_STATE_RDY)
> >                 return;
> >
> >         if (modify_virtqueue(ndev, mvq, MLX5_VIRTIO_NET_Q_OBJECT_STATE_SUSPEND))
> >                 mlx5_vdpa_warn(&ndev->mvdev, "modify to suspend failed\n");
> > +
> > +       if (query_virtqueue(ndev, mvq, &attr)) {
> > +               mlx5_vdpa_warn(&ndev->mvdev, "failed to query virtqueue\n");
> > +               return;
> > +       }
> > +       mvq->avail_idx = attr.available_index;
> >  }
> >
> >  static void suspend_vqs(struct mlx5_vdpa_net *ndev)
> > @@ -1411,8 +1413,14 @@ static int mlx5_vdpa_get_vq_state(struct vdpa_device *vdev, u16 idx, struct vdpa
> >         struct mlx5_virtq_attr attr;
> >         int err;
> >
> > -       if (!mvq->initialized)
> > -               return -EAGAIN;
> > +       /* If the virtq object was destroyed, use the value saved at
> > +        * the last minute of suspend_vq. This caters for userspace
> > +        * that cares about emulating the index after vq is stopped.
> > +        */
> > +       if (!mvq->initialized) {
> > +               state->avail_index = mvq->avail_idx;
> > +               return 0;
> > +       }
> >
> >         err = query_virtqueue(ndev, mvq, &attr);
> >         if (err) {
> > --
> > 1.8.3.1
> >