vdpa/mlx5: Re-create HW VQs under certain conditions

There are a few conditions under which the hardware VQs need a full
teardown and setup:

- VQ size changed to something else than default value. Hardware VQ size
  modification is not supported.

- User turns off certain device features: mergeable buffers, checksum
  virtio 1.0 compliance. In these cases, the TIR and RQT need to be
  re-created.

Add a needs_teardown configuration variable and set it when detecting
the above scenarios. On next DRIVER_OK, the resources will be torn down
first.
Reviewed-by: Cosmin Ratiu <cratiu@nvidia.com>
Acked-by: Eugenio Pérez <eperezma@redhat.com>
Signed-off-by: Dragos Tatulea <dtatulea@nvidia.com>
Message-Id: <20240626-stage-vdpa-vq-precreate-v2-22-560c491078df@nvidia.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>

drivers/vdpa/mlx5/net/mlx5_vnet.c

@@ -2390,6 +2390,7 @@ static void mlx5_vdpa_set_vq_num(struct vdpa_device *vdev, u16 idx, u32 num)
         }
 
 	mvq = &ndev->vqs[idx];
+	ndev->needs_teardown = num != mvq->num_ent;
 	mvq->num_ent = num;
 }
 
@@ -2800,6 +2801,7 @@ static int mlx5_vdpa_set_driver_features(struct vdpa_device *vdev, u64 features)
 	struct mlx5_vdpa_dev *mvdev = to_mvdev(vdev);
 	struct mlx5_vdpa_net *ndev = to_mlx5_vdpa_ndev(mvdev);
 	u64 old_features = mvdev->actual_features;
+	u64 diff_features;
 	int err;
 
 	print_features(mvdev, features, true);
@@ -2822,6 +2824,14 @@ static int mlx5_vdpa_set_driver_features(struct vdpa_device *vdev, u64 features)
 		}
 	}
 
+	/* When below features diverge from initial device features, VQs need a full teardown. */
+#define NEEDS_TEARDOWN_MASK (BIT_ULL(VIRTIO_NET_F_MRG_RXBUF) | \
+			     BIT_ULL(VIRTIO_NET_F_CSUM) | \
+			     BIT_ULL(VIRTIO_F_VERSION_1))
+
+	diff_features = mvdev->mlx_features ^ mvdev->actual_features;
+	ndev->needs_teardown = !!(diff_features & NEEDS_TEARDOWN_MASK);
+
 	update_cvq_info(mvdev);
 	return err;
 }
@@ -3038,6 +3048,7 @@ static void teardown_vq_resources(struct mlx5_vdpa_net *ndev)
 	destroy_rqt(ndev);
 	teardown_virtqueues(ndev);
 	ndev->setup = false;
+	ndev->needs_teardown = false;
 }
 
 static int setup_cvq_vring(struct mlx5_vdpa_dev *mvdev)
@@ -3078,6 +3089,10 @@ static void mlx5_vdpa_set_status(struct vdpa_device *vdev, u8 status)
 				goto err_setup;
 			}
 			register_link_notifier(ndev);
+
+			if (ndev->needs_teardown)
+				teardown_vq_resources(ndev);
+
 			if (ndev->setup) {
 				err = resume_vqs(ndev);
 				if (err) {

drivers/vdpa/mlx5/net/mlx5_vnet.h

@@ -56,6 +56,7 @@ struct mlx5_vdpa_net {
 	struct dentry *rx_dent;
 	struct dentry *rx_table_dent;
 	bool setup;
+	bool needs_teardown;
 	u32 cur_num_vqs;
 	u32 rqt_size;
 	bool nb_registered;