[PATCH 1/2] vdpa: mlx5: prevent cvq work from hogging CPU

[Jason Wang <jasowang@redhat.com>]

A userspace triggerable infinite loop could happen in
mlx5_cvq_kick_handler() if userspace keeps sending a huge amount of
cvq requests.

Fixing this by introducing a quota and re-queue the work if we're out
of the budget. While at it, using a per device workqueue to avoid on
demand memory allocation for cvq.

Fixes: 5262912ef3cfc ("vdpa/mlx5: Add support for control VQ and MAC setting")
Signed-off-by: Jason Wang <jasowang@redhat.com>
---
 drivers/vdpa/mlx5/net/mlx5_vnet.c | 28 +++++++++++++++-------------
 1 file changed, 15 insertions(+), 13 deletions(-)

diff --git a/drivers/vdpa/mlx5/net/mlx5_vnet.c b/drivers/vdpa/mlx5/net/mlx5_vnet.c
index d0f91078600e..d5a6fb3f9c41 100644
--- a/drivers/vdpa/mlx5/net/mlx5_vnet.c
+++ b/drivers/vdpa/mlx5/net/mlx5_vnet.c
@@ -163,6 +163,7 @@ struct mlx5_vdpa_net {
 	u32 cur_num_vqs;
 	struct notifier_block nb;
 	struct vdpa_callback config_cb;
+	struct mlx5_vdpa_wq_ent cvq_ent;
 };
 
 static void free_resources(struct mlx5_vdpa_net *ndev);
@@ -1600,6 +1601,8 @@ static virtio_net_ctrl_ack handle_ctrl_mq(struct mlx5_vdpa_dev *mvdev, u8 cmd)
 	return status;
 }
 
+#define MLX5_CVQ_BUDGET 16
+
 static void mlx5_cvq_kick_handler(struct work_struct *work)
 {
 	virtio_net_ctrl_ack status = VIRTIO_NET_ERR;
@@ -1609,17 +1612,17 @@ static void mlx5_cvq_kick_handler(struct work_struct *work)
 	struct mlx5_control_vq *cvq;
 	struct mlx5_vdpa_net *ndev;
 	size_t read, write;
-	int err;
+	int err, n = 0;
 
 	wqent = container_of(work, struct mlx5_vdpa_wq_ent, work);
 	mvdev = wqent->mvdev;
 	ndev = to_mlx5_vdpa_ndev(mvdev);
 	cvq = &mvdev->cvq;
 	if (!(ndev->mvdev.actual_features & BIT_ULL(VIRTIO_NET_F_CTRL_VQ)))
-		goto out;
+		return;
 
 	if (!cvq->ready)
-		goto out;
+		return;
 
 	while (true) {
 		err = vringh_getdesc_iotlb(&cvq->vring, &cvq->riov, &cvq->wiov, &cvq->head,
@@ -1653,9 +1656,13 @@ static void mlx5_cvq_kick_handler(struct work_struct *work)
 
 		if (vringh_need_notify_iotlb(&cvq->vring))
 			vringh_notify(&cvq->vring);
+
+		n++;
+		if (n > MLX5_CVQ_BUDGET) {
+			queue_work(mvdev->wq, &wqent->work);
+			break;
+		}
 	}
-out:
-	kfree(wqent);
 }
 
 static void mlx5_vdpa_kick_vq(struct vdpa_device *vdev, u16 idx)
@@ -1663,7 +1670,6 @@ static void mlx5_vdpa_kick_vq(struct vdpa_device *vdev, u16 idx)
 	struct mlx5_vdpa_dev *mvdev = to_mvdev(vdev);
 	struct mlx5_vdpa_net *ndev = to_mlx5_vdpa_ndev(mvdev);
 	struct mlx5_vdpa_virtqueue *mvq;
-	struct mlx5_vdpa_wq_ent *wqent;
 
 	if (!is_index_valid(mvdev, idx))
 		return;
@@ -1672,13 +1678,7 @@ static void mlx5_vdpa_kick_vq(struct vdpa_device *vdev, u16 idx)
 		if (!mvdev->cvq.ready)
 			return;
 
-		wqent = kzalloc(sizeof(*wqent), GFP_ATOMIC);
-		if (!wqent)
-			return;
-
-		wqent->mvdev = mvdev;
-		INIT_WORK(&wqent->work, mlx5_cvq_kick_handler);
-		queue_work(mvdev->wq, &wqent->work);
+		queue_work(mvdev->wq, &ndev->cvq_ent.work);
 		return;
 	}
 
@@ -2668,6 +2668,8 @@ static int mlx5_vdpa_dev_add(struct vdpa_mgmt_dev *v_mdev, const char *name,
 	if (err)
 		goto err_mr;
 
+	ndev->cvq_ent.mvdev = mvdev;
+	INIT_WORK(&ndev->cvq_ent.work, mlx5_cvq_kick_handler);
 	mvdev->wq = create_singlethread_workqueue("mlx5_vdpa_wq");
 	if (!mvdev->wq) {
 		err = -ENOMEM;
-- 
2.18.1