Re: [PATCH v2 3/3] vdpa/mlx5: defer clear_virtqueues to until DRIVER_OK

[Si-Wei Liu]

On 2/16/2021 7:21 AM, Eli Cohen wrote:
> On Thu, Feb 11, 2021 at 09:33:14AM +0200, Eli Cohen wrote:
> > On Wed, Feb 10, 2021 at 01:48:00PM -0800, Si-Wei Liu wrote:
> > > While virtq is stopped,  get_vq_state() is supposed to
> > > be  called to  get  sync'ed  with  the latest internal
> > > avail_index from device. The saved avail_index is used
> > > to restate  the virtq  once device is started.  Commit
> > > b35ccebe3ef7 introduced the clear_virtqueues() routine
> > > to  reset  the saved  avail_index,  however, the index
> > > gets cleared a bit earlier before get_vq_state() tries
> > > to read it. This would cause consistency problems when
> > > virtq is restarted, e.g. through a series of link down
> > > and link up events. We  could  defer  the  clearing of
> > > avail_index  to  until  the  device  is to be started,
> > > i.e. until  VIRTIO_CONFIG_S_DRIVER_OK  is set again in
> > > set_status().
> > >
> > > Fixes: b35ccebe3ef7 ("vdpa/mlx5: Restore the hardware used index after change map")
> > > Signed-off-by: Si-Wei Liu <si-wei.liu@xxxxxxxxxx>
> > > Acked-by: Jason Wang <jasowang@xxxxxxxxxx>
> > Acked-by: Eli Cohen <elic@xxxxxxxxxx>
> I take it back. I think we don't need to clear the indexes at all. In
> case we need to restore indexes we'll get the right values through
> set_vq_state(). If we suspend the virtqueue due to VM being suspended,
> qemu will query first and will provide the the queried value. In case of
> VM reboot, it will provide 0 in set_vq_state().
>
> I am sending a patch that addresses both reboot and suspend.
With set_vq_state() repurposed to restoring used_index I'm fine with 
this approach.

Do I have to repost a v3 of this series while dropping the 3rd patch?

-Siwei
> > > ---
> > >   drivers/vdpa/mlx5/net/mlx5_vnet.c | 2 +-
> > >   1 file changed, 1 insertion(+), 1 deletion(-)
> > >
> > > diff --git a/drivers/vdpa/mlx5/net/mlx5_vnet.c b/drivers/vdpa/mlx5/net/mlx5_vnet.c
> > > index 7c1f789..ce6aae8 100644
> > > --- a/drivers/vdpa/mlx5/net/mlx5_vnet.c
> > > +++ b/drivers/vdpa/mlx5/net/mlx5_vnet.c
> > > @@ -1777,7 +1777,6 @@ static void mlx5_vdpa_set_status(struct vdpa_device *vdev, u8 status)
> > >   	if (!status) {
> > >   		mlx5_vdpa_info(mvdev, "performing device reset\n");
> > >   		teardown_driver(ndev);
> > > -		clear_virtqueues(ndev);
> > >   		mlx5_vdpa_destroy_mr(&ndev->mvdev);
> > >   		ndev->mvdev.status = 0;
> > >   		++mvdev->generation;
> > > @@ -1786,6 +1785,7 @@ static void mlx5_vdpa_set_status(struct vdpa_device *vdev, u8 status)
> > >   
> > >   	if ((status ^ ndev->mvdev.status) & VIRTIO_CONFIG_S_DRIVER_OK) {
> > >   		if (status & VIRTIO_CONFIG_S_DRIVER_OK) {
> > > +			clear_virtqueues(ndev);
> > >   			err = setup_driver(ndev);
> > >   			if (err) {
> > >   				mlx5_vdpa_warn(mvdev, "failed to setup driver\n");
> > > --
> > > 1.8.3.1