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Date:   Tue, 6 Oct 2020 09:42:51 +0300
From:   Eli Cohen <elic@nvidia.com>
To:     "Michael S. Tsirkin" <mst@redhat.com>
CC:     Si-Wei Liu <siwliu.kernel@gmail.com>, <jasowang@redhat.com>,
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Subject: Re: [PATCH] vdpa/mlx5: should keep avail_index despite device status
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On Tue, Oct 06, 2020 at 02:22:15AM -0400, Michael S. Tsirkin wrote:

Acked-by: Eli Cohen <elic@nvidia.com>

> 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 <si-wei.liu@oracle.com> 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 <si-wei.liu@oracle.com>
> 
> 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
> > >
>