Subject: Re: [PATCH 1/2] vdpa/mlx5: Fix suspend/resume index restoration

From: "Michael S. Tsirkin" <[email-masked]>
Date: Wed, 17 Feb 2021 16:20:14 -0500

On Wed, Feb 17, 2021 at 11:42:48AM -0800, Si-Wei Liu wrote:
> 
> 
> On 2/16/2021 8:20 AM, Eli Cohen wrote:
> > When we suspend the VM, the VDPA interface will be reset. When the VM is
> > resumed again, clear_virtqueues() will clear the available and used
> > indices resulting in hardware virqtqueue objects becoming out of sync.
> > We can avoid this function alltogether since qemu will clear them if
> > required, e.g. when the VM went through a reboot.
> > 
> > Moreover, since the hw available and used indices should always be
> > identical on query and should be restored to the same value same value
> > for virtqueues that complete in order, we set the single value provided
> > by set_vq_state(). In get_vq_state() we return the value of hardware
> > used index.
> > 
> > Fixes: 1a86b377aa21 ("vdpa/mlx5: Add VDPA driver for supported mlx5 devices")
> > Signed-off-by: Eli Cohen <[email-masked]>
> Acked-by: Si-Wei Liu <[email-masked]>

Seems to also fix b35ccebe3ef76168aa2edaa35809c0232cb3578e, right?

> > ---
> >   drivers/vdpa/mlx5/net/mlx5_vnet.c | 17 ++++-------------
> >   1 file changed, 4 insertions(+), 13 deletions(-)
> > 
> > diff --git a/drivers/vdpa/mlx5/net/mlx5_vnet.c b/drivers/vdpa/mlx5/net/mlx5_vnet.c
> > index b8e9d525d66c..a51b0f86afe2 100644
> > --- a/drivers/vdpa/mlx5/net/mlx5_vnet.c
> > +++ b/drivers/vdpa/mlx5/net/mlx5_vnet.c
> > @@ -1169,6 +1169,7 @@ static void suspend_vq(struct mlx5_vdpa_net *ndev, struct mlx5_vdpa_virtqueue *m
> >   		return;
> >   	}
> >   	mvq->avail_idx = attr.available_index;
> > +	mvq->used_idx = attr.used_index;
> >   }
> >   static void suspend_vqs(struct mlx5_vdpa_net *ndev)
> > @@ -1426,6 +1427,7 @@ static int mlx5_vdpa_set_vq_state(struct vdpa_device *vdev, u16 idx,
> >   		return -EINVAL;
> >   	}
> > +	mvq->used_idx = state->avail_index;
> >   	mvq->avail_idx = state->avail_index;
> >   	return 0;
> >   }
> > @@ -1443,7 +1445,7 @@ static int mlx5_vdpa_get_vq_state(struct vdpa_device *vdev, u16 idx, struct vdpa
> >   	 * that cares about emulating the index after vq is stopped.
> >   	 */
> >   	if (!mvq->initialized) {
> > -		state->avail_index = mvq->avail_idx;
> > +		state->avail_index = mvq->used_idx;
> >   		return 0;
> >   	}
> > @@ -1452,7 +1454,7 @@ static int mlx5_vdpa_get_vq_state(struct vdpa_device *vdev, u16 idx, struct vdpa
> >   		mlx5_vdpa_warn(mvdev, "failed to query virtqueue\n");
> >   		return err;
> >   	}
> > -	state->avail_index = attr.available_index;
> > +	state->avail_index = attr.used_index;
> >   	return 0;
> >   }
> > @@ -1532,16 +1534,6 @@ static void teardown_virtqueues(struct mlx5_vdpa_net *ndev)
> >   	}
> >   }
> > -static void clear_virtqueues(struct mlx5_vdpa_net *ndev)
> > -{
> > -	int i;
> > -
> > -	for (i = ndev->mvdev.max_vqs - 1; i >= 0; i--) {
> > -		ndev->vqs[i].avail_idx = 0;
> > -		ndev->vqs[i].used_idx = 0;
> > -	}
> > -}
> > -
> >   /* TODO: cross-endian support */
> >   static inline bool mlx5_vdpa_is_little_endian(struct mlx5_vdpa_dev *mvdev)
> >   {
> > @@ -1777,7 +1769,6 @@ 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;