vdpa/mlx5: Allow CVQ size changes

The MLX driver was not updating its control virtqueue size at set_vq_num
and instead always initialized to MLX5_CVQ_MAX_ENT (16) at
setup_cvq_vring.

Qemu would try to set the size to 64 by default, however, because the
CVQ size always was initialized to 16, an error would be thrown when
sending >16 control messages (as used-ring entry 17 is initialized to 0).
For example, starting a guest with x-svq=on and then executing the
following command would produce the error below:

 # for i in {1..20}; do ifconfig eth0 hw ether XX:xx:XX:xx:XX:XX; done

 qemu-system-x86_64: Insufficient written data (0)
 [  435.331223] virtio_net virtio0: Failed to set mac address by vq command.
 SIOCSIFHWADDR: Invalid argument
Acked-by: Dragos Tatulea <dtatulea@nvidia.com>
Acked-by: Eugenio Pérez <eperezma@redhat.com>
Signed-off-by: Jonah Palmer <jonah.palmer@oracle.com>
Message-Id: <20240216142502.78095-1-jonah.palmer@oracle.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
Tested-by: Lei Yang <leiyang@redhat.com>
Fixes: 5262912e ("vdpa/mlx5: Add support for control VQ and MAC setting")

drivers/vdpa/mlx5/net/mlx5_vnet.c

@@ -151,8 +151,6 @@ static void teardown_driver(struct mlx5_vdpa_net *ndev);
 
 static bool mlx5_vdpa_debug;
 
-#define MLX5_CVQ_MAX_ENT 16
-
 #define MLX5_LOG_VIO_FLAG(_feature)                                                                \
 	do {                                                                                       \
 		if (features & BIT_ULL(_feature))                                                  \
@@ -2276,9 +2274,16 @@ static void mlx5_vdpa_set_vq_num(struct vdpa_device *vdev, u16 idx, u32 num)
 	struct mlx5_vdpa_net *ndev = to_mlx5_vdpa_ndev(mvdev);
 	struct mlx5_vdpa_virtqueue *mvq;
 
-	if (!is_index_valid(mvdev, idx) || is_ctrl_vq_idx(mvdev, idx))
+	if (!is_index_valid(mvdev, idx))
 		return;
 
+        if (is_ctrl_vq_idx(mvdev, idx)) {
+                struct mlx5_control_vq *cvq = &mvdev->cvq;
+
+                cvq->vring.vring.num = num;
+                return;
+        }
+
 	mvq = &ndev->vqs[idx];
 	mvq->num_ent = num;
 }
@@ -2963,7 +2968,7 @@ static int setup_cvq_vring(struct mlx5_vdpa_dev *mvdev)
 		u16 idx = cvq->vring.last_avail_idx;
 
 		err = vringh_init_iotlb(&cvq->vring, mvdev->actual_features,
-					MLX5_CVQ_MAX_ENT, false,
+					cvq->vring.vring.num, 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);