[PATCH V3] vdpa/mlx5: preserve CVQ vringh index

[Steve Sistare]

mlx5_vdpa does not preserve userland's view of vring base for the control
queue in the following sequence:

ioctl VHOST_SET_VRING_BASE
ioctl VHOST_VDPA_SET_STATUS VIRTIO_CONFIG_S_DRIVER_OK
  mlx5_vdpa_set_status()
    setup_cvq_vring()
      vringh_init_iotlb()
        vringh_init_kern()
          vrh->last_avail_idx = 0;
ioctl VHOST_GET_VRING_BASE

To fix, restore the value of cvq->vring.last_avail_idx after calling
vringh_init_iotlb.

Fixes: 5262912ef3cf ("vdpa/mlx5: Add support for control VQ and MAC setting")

Signed-off-by: Steve Sistare <steven.sistare@xxxxxxxxxx>
Acked-by: Eugenio Pérez <eperezma@xxxxxxxxxx>
Acked-by: Jason Wang <jasowang@xxxxxxxxxx>
---
 drivers/vdpa/mlx5/net/mlx5_vnet.c | 7 ++++++-
 1 file changed, 6 insertions(+), 1 deletion(-)

diff --git a/drivers/vdpa/mlx5/net/mlx5_vnet.c b/drivers/vdpa/mlx5/net/mlx5_vnet.c
index 946488b8989f..ca972af3c89a 100644
--- a/drivers/vdpa/mlx5/net/mlx5_vnet.c
+++ b/drivers/vdpa/mlx5/net/mlx5_vnet.c
@@ -2795,13 +2795,18 @@ static int setup_cvq_vring(struct mlx5_vdpa_dev *mvdev)
 	struct mlx5_control_vq *cvq = &mvdev->cvq;
 	int err = 0;
 
-	if (mvdev->actual_features & BIT_ULL(VIRTIO_NET_F_CTRL_VQ))
+	if (mvdev->actual_features & BIT_ULL(VIRTIO_NET_F_CTRL_VQ)) {
+		u16 idx = cvq->vring.last_avail_idx;
+
 		err = vringh_init_iotlb(&cvq->vring, mvdev->actual_features,
 					MLX5_CVQ_MAX_ENT, false,
 					(struct vring_desc *)(uintptr_t)cvq->desc_addr,
 					(struct vring_avail *)(uintptr_t)cvq->driver_addr,
 					(struct vring_used *)(uintptr_t)cvq->device_addr);
 
+		if (!err)
+			cvq->vring.last_avail_idx = cvq->vring.last_used_idx = idx;
+	}
 	return err;
 }
 
-- 
2.39.3