vdpa: mlx5: prevent cvq work from hogging CPU

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 (currently the implicit budget is one) . While at it,
using a per device work struct 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>
Link: https://lore.kernel.org/r/20220329042109.4029-1-jasowang@redhat.com
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
Acked-by: Eli Cohen <elic@nvidia.com>

diff --git a/drivers/vdpa/mlx5/net/mlx5_vnet.c b/drivers/vdpa/mlx5/net/mlx5_vnet.c
index 2f4fb09..da21e54 100644 (file)
--- 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);
@@ -1659,10 +1660,10 @@ static void mlx5_cvq_kick_handler(struct work_struct *work)
        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,
@@ -1696,9 +1697,10 @@ static void mlx5_cvq_kick_handler(struct work_struct *work)
 
                if (vringh_need_notify_iotlb(&cvq->vring))
                        vringh_notify(&cvq->vring);
+
+               queue_work(mvdev->wq, &wqent->work);
+               break;
        }
-out:
-       kfree(wqent);
 }
 
 static void mlx5_vdpa_kick_vq(struct vdpa_device *vdev, u16 idx)
@@ -1706,7 +1708,6 @@ 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;
@@ -1715,13 +1716,7 @@ static void mlx5_vdpa_kick_vq(struct vdpa_device *vdev, u16 idx)
                if (!mvdev->wq || !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;
        }
 
@@ -2740,6 +2735,8 @@ 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;