[PATCH vhost v2 23/24] vdpa/mlx5: Don't reset VQs more than necessary

[Dragos Tatulea]

The vdpa device can be reset many times in sequence without any
significant state changes in between. Previously this was not a problem:
VQs were torn down only on first reset. But after VQ pre-creation was
introduced, each reset will delete and re-create the hardware VQs and
their associated resources.

To solve this problem, avoid resetting hardware VQs if the VQs are still
in a blank state.

Reviewed-by: Cosmin Ratiu <cra...@nvidia.com>
Acked-by: Eugenio Pérez <epere...@redhat.com>
Signed-off-by: Dragos Tatulea <dtatu...@nvidia.com>
---
 drivers/vdpa/mlx5/net/mlx5_vnet.c | 30 +++++++++++++++++++++++++++---
 1 file changed, 27 insertions(+), 3 deletions(-)

diff --git a/drivers/vdpa/mlx5/net/mlx5_vnet.c 
b/drivers/vdpa/mlx5/net/mlx5_vnet.c
index ea4bfd9afce9..573dc01df8c3 100644
--- a/drivers/vdpa/mlx5/net/mlx5_vnet.c
+++ b/drivers/vdpa/mlx5/net/mlx5_vnet.c
@@ -3134,18 +3134,41 @@ static void init_group_to_asid_map(struct mlx5_vdpa_dev 
*mvdev)
                mvdev->group2asid[i] = 0;
 }
 
+static bool needs_vqs_reset(const struct mlx5_vdpa_dev *mvdev)
+{
+       struct mlx5_vdpa_net *ndev = to_mlx5_vdpa_ndev(mvdev);
+       struct mlx5_vdpa_virtqueue *mvq = &ndev->vqs[0];
+
+       if (mvdev->status & VIRTIO_CONFIG_S_DRIVER_OK)
+               return true;
+
+       if (mvq->fw_state != MLX5_VIRTIO_NET_Q_OBJECT_STATE_INIT)
+               return true;
+
+       return mvq->modified_fields & (
+               MLX5_VIRTQ_MODIFY_MASK_STATE |
+               MLX5_VIRTQ_MODIFY_MASK_VIRTIO_Q_ADDRS |
+               MLX5_VIRTQ_MODIFY_MASK_VIRTIO_Q_AVAIL_IDX |
+               MLX5_VIRTQ_MODIFY_MASK_VIRTIO_Q_USED_IDX
+       );
+}
+
 static int mlx5_vdpa_compat_reset(struct vdpa_device *vdev, u32 flags)
 {
        struct mlx5_vdpa_dev *mvdev = to_mvdev(vdev);
        struct mlx5_vdpa_net *ndev = to_mlx5_vdpa_ndev(mvdev);
+       bool vq_reset;
 
        print_status(mvdev, 0, true);
        mlx5_vdpa_info(mvdev, "performing device reset\n");
 
        down_write(&ndev->reslock);
        unregister_link_notifier(ndev);
-       teardown_vq_resources(ndev);
-       mvqs_set_defaults(ndev);
+       vq_reset = needs_vqs_reset(mvdev);
+       if (vq_reset) {
+               teardown_vq_resources(ndev);
+               mvqs_set_defaults(ndev);
+       }
 
        if (flags & VDPA_RESET_F_CLEAN_MAP)
                mlx5_vdpa_destroy_mr_resources(&ndev->mvdev);
@@ -3165,7 +3188,8 @@ static int mlx5_vdpa_compat_reset(struct vdpa_device 
*vdev, u32 flags)
                if (mlx5_vdpa_create_dma_mr(mvdev))
                        mlx5_vdpa_warn(mvdev, "create MR failed\n");
        }
-       setup_vq_resources(ndev, false);
+       if (vq_reset)
+               setup_vq_resources(ndev, false);
        up_write(&ndev->reslock);
 
        return 0;

-- 
2.45.1