Re: [PATCH 4/4] vdpa/mlx5: Fix tracking of current number of VQs

[Jason Wang <jasowang@redhat.com>]

On Wed, Jan 12, 2022 at 6:15 AM Si-Wei Liu <si-wei.liu@oracle.com> wrote:
>
>
>
> On 1/11/2022 10:34 AM, Eli Cohen wrote:
> > Modify the code such that ndev->cur_num_vqs better reflects the actual
> > number of data virtqueues. The value can be accurately realized after
> > features have been negotiated.
> >
> > This is to prevent possible failures when modifying the RQT object if
> > the cur_num_vqs bears invalid value.
> >
> > No issue was actually encountered but this also makes the code more
> > readable.
> >
> > Fixes: c5a5cd3d3217 ("vdpa/mlx5: Support configuring max data virtqueue")
> > Signed-off-by: Eli Cohen <elic@nvidia.com>
> > ---
> >   drivers/vdpa/mlx5/net/mlx5_vnet.c | 12 ++++++++----
> >   1 file changed, 8 insertions(+), 4 deletions(-)
> >
> > diff --git a/drivers/vdpa/mlx5/net/mlx5_vnet.c b/drivers/vdpa/mlx5/net/mlx5_vnet.c
> > index 9eacfdb48434..b53603d94082 100644
> > --- a/drivers/vdpa/mlx5/net/mlx5_vnet.c
> > +++ b/drivers/vdpa/mlx5/net/mlx5_vnet.c
> > @@ -1246,8 +1246,7 @@ static int create_rqt(struct mlx5_vdpa_net *ndev)
> >       if (!(ndev->mvdev.actual_features & BIT_ULL(VIRTIO_NET_F_MQ)))
> >               num = 1;
> >       else
> > -             num = mlx5vdpa16_to_cpu(&ndev->mvdev,
> > -                                     ndev->config.max_virtqueue_pairs);
> > +             num = ndev->cur_num_vqs / 2;
> Nit: the if branch can be consolidated
>
> >
> >       max_rqt = min_t(int, roundup_pow_of_two(num),
> >                       1 << MLX5_CAP_GEN(ndev->mvdev.mdev, log_max_rqt_size));
> > @@ -1983,6 +1982,11 @@ static int mlx5_vdpa_set_driver_features(struct vdpa_device *vdev, u64 features)
> >               return err;
> >
> >       ndev->mvdev.actual_features = features & ndev->mvdev.mlx_features;
> > +     if (ndev->mvdev.actual_features & BIT_ULL(VIRTIO_NET_F_MQ))
> > +             ndev->cur_num_vqs = 2 * mlx5vdpa16_to_cpu(mvdev, ndev->config.max_virtqueue_pairs);
> Hmmm, not this patch, but there should've been validation done in the
> upper layer to guarantee set_featuers() for VIRTIO_NET_F_MQ always comes
> with VIRTIO_NET_F_CTRL_VQ. Maybe checking both: BIT_ULL(VIRTIO_NET_F_MQ)
> |  BIT_ULL(VIRTIO_NET_F_CTRL_VQ)?

So the upper layer is unaware of the device type. It's better to do
that in mlx5's set_features() according to the spec:

The device MUST NOT offer a feature which requires another feature
which was not offered.

Thanks

>
> otherwise it looks good to me.
>
> Reviewed-by: Si-Wei Liu<si-wei.liu@oracle.com>
> > +     else
> > +             ndev->cur_num_vqs = 2;
> > +
> >       update_cvq_info(mvdev);
> >       return err;
> >   }
> > @@ -2233,6 +2237,7 @@ static int mlx5_vdpa_reset(struct vdpa_device *vdev)
> >       clear_vqs_ready(ndev);
> >       mlx5_vdpa_destroy_mr(&ndev->mvdev);
> >       ndev->mvdev.status = 0;
> > +     ndev->cur_num_vqs = 0;
> >       memset(ndev->event_cbs, 0, sizeof(*ndev->event_cbs) * (mvdev->max_vqs + 1));
> >       ndev->mvdev.actual_features = 0;
> >       ++mvdev->generation;
> > @@ -2641,9 +2646,8 @@ static int mlx5_vdpa_dev_add(struct vdpa_mgmt_dev *v_mdev, const char *name,
> >
> >       ndev->nb.notifier_call = event_handler;
> >       mlx5_notifier_register(mdev, &ndev->nb);
> > -     ndev->cur_num_vqs = 2 * mlx5_vdpa_max_qps(max_vqs);
> >       mvdev->vdev.mdev = &mgtdev->mgtdev;
> > -     err = _vdpa_register_device(&mvdev->vdev, ndev->cur_num_vqs + 1);
> > +     err = _vdpa_register_device(&mvdev->vdev, 2 * mlx5_vdpa_max_qps(max_vqs) + 1);
> >       if (err)
> >               goto err_reg;
> >
>

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