Re: [PATCH 1/2] vdpa/mlx5: Avoid unnecessary query virtqueue

[Jason Wang]

On 2021/2/2 上午3:17, Si-Wei Liu wrote:
> On Mon, Feb 1, 2021 at 10:51 AM Si-Wei Liu <siwliu.kernel@xxxxxxxxx> wrote:
> > On Thu, Jan 28, 2021 at 5:46 AM Eli Cohen <elic@xxxxxxxxxx> wrote:
> > > suspend_vq should only suspend the VQ on not save the current available
> > > index. This is done when a change of map occurs when the driver calls
> > > save_channel_info().
> > Hmmm, suspend_vq() is also called by teardown_vq(), the latter of
> > which doesn't save the available index as save_channel_info() doesn't
> > get called in that path at all. How does it handle the case that
> > aget_vq_state() is called from userspace (e.g. QEMU) while the
> > hardware VQ object was torn down, but userspace still wants to access
> > the queue index?
> >
> > Refer to https://lore.kernel.org/netdev/1601583511-15138-1-git-send-email-si-wei.liu@xxxxxxxxxx/
> >
> > vhost VQ 0 ring restore failed: -1: Resource temporarily unavailable (11)
> > vhost VQ 1 ring restore failed: -1: Resource temporarily unavailable (11)
> >
> > QEMU will complain with the above warning while VM is being rebooted
> > or shut down.
> >
> > Looks to me either the kernel driver should cover this requirement, or
> > the userspace has to bear the burden in saving the index and not call
> > into kernel if VQ is destroyed.
> Actually, the userspace doesn't have the insights whether virt queue
> will be destroyed if just changing the device status via set_status().
> Looking at other vdpa driver in tree i.e. ifcvf it doesn't behave like
> so. Hence this still looks to me to be Mellanox specifics and
> mlx5_vdpa implementation detail that shouldn't expose to userspace.


So I think we can simply drop this patch?

Thanks


> > -Siwei
> >
> >
> > > Signed-off-by: Eli Cohen <elic@xxxxxxxxxx>
> > > ---
> > >   drivers/vdpa/mlx5/net/mlx5_vnet.c | 8 --------
> > >   1 file changed, 8 deletions(-)
> > >
> > > diff --git a/drivers/vdpa/mlx5/net/mlx5_vnet.c b/drivers/vdpa/mlx5/net/mlx5_vnet.c
> > > index 88dde3455bfd..549ded074ff3 100644
> > > --- a/drivers/vdpa/mlx5/net/mlx5_vnet.c
> > > +++ b/drivers/vdpa/mlx5/net/mlx5_vnet.c
> > > @@ -1148,8 +1148,6 @@ static int setup_vq(struct mlx5_vdpa_net *ndev, struct mlx5_vdpa_virtqueue *mvq)
> > >
> > >   static void suspend_vq(struct mlx5_vdpa_net *ndev, struct mlx5_vdpa_virtqueue *mvq)
> > >   {
> > > -       struct mlx5_virtq_attr attr;
> > > -
> > >          if (!mvq->initialized)
> > >                  return;
> > >
> > > @@ -1158,12 +1156,6 @@ static void suspend_vq(struct mlx5_vdpa_net *ndev, struct mlx5_vdpa_virtqueue *m
> > >
> > >          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)
> > > --
> > > 2.29.2