[PATCH 5.16 159/285] vdpa: mlx5: prevent cvq work from hogging CPU

Greg Kroah-Hartman
2022-04-12T08:29:55Z

From: Jason Wang <jasowang@redhat.com>

[ Upstream commit 55ebf0d60e3cc6c9e8593399e185842c00e12f36 ]

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>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
drivers/vdpa/mlx5/net/mlx5_vnet.c | 21 +++++++++------------
1 file changed, 9 insertions(+), 12 deletions(-)

diff --git a/drivers/vdpa/mlx5/net/mlx5_vnet.c b/drivers/vdpa/mlx5/net/mlx5_vnet.c
index 57bed3d74060..be50c15609b7 100644
--- a/drivers/vdpa/mlx5/net/mlx5_vnet.c
+++ b/drivers/vdpa/mlx5/net/mlx5_vnet.c
@@ -164,6 +164,7 @@ 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);
@@ -1627,10 +1628,10 @@ 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,
@@ -1664,9 +1665,10 @@ 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)
@@ -1674,7 +1676,6 @@ 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;
@@ -1683,13 +1684,7 @@ 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;
}

@@ -2634,6 +2629,8 @@ 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;
--
2.35.1