Virtualization - Dec 2022 - [PATCH 0/4] virtio-net: don't busy poll for cvq command

Hi all:

The code used to busy poll for cvq command which turns out to have
several side effects:

1) infinite poll for buggy devices
2) bad interaction with scheduler

So this series tries to use sleep + timeout instead of busy polling.

Please review.

Thanks

Changes since RFC:

- switch to use BAD_RING in virtio_break_device()
- check virtqueue_is_broken() after being woken up
- use more_used() instead of virtqueue_get_buf() to allow caller to
  get buffers afterwards
- break the virtio-net device when timeout
- get buffer manually since the virtio core check more_used() instead

Jason Wang (4):
  virtio-net: convert rx mode setting to use workqueue
  virtio_ring: switch to use BAD_RING()
  virtio_ring: introduce a per virtqueue waitqueue
  virtio-net: sleep instead of busy waiting for cvq command

 drivers/net/virtio_net.c     | 90 +++++++++++++++++++++++++++++++-----
 drivers/virtio/virtio_ring.c | 37 +++++++++++++--
 include/linux/virtio.h       |  3 ++
 3 files changed, 115 insertions(+), 15 deletions(-)

-- 
2.25.1

This patch convert rx mode setting to be done in a workqueue, this is
a must for allow to sleep when waiting for the cvq command to
response since current code is executed under addr spin lock.

Signed-off-by: Jason Wang <jasowang at redhat.com>
---
 drivers/net/virtio_net.c | 66 ++++++++++++++++++++++++++++++++++++++--
 1 file changed, 63 insertions(+), 3 deletions(-)

diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c
index 86e52454b5b5..efd9dd55828b 100644
--- a/drivers/net/virtio_net.c
+++ b/drivers/net/virtio_net.c
@@ -260,6 +260,15 @@ struct virtnet_info {
 	/* Work struct for config space updates */
 	struct work_struct config_work;
 
+	/* Work struct for config rx mode */
+	struct work_struct rx_mode_work;
+
+	/* Is rx_mode_work enabled? */
+	bool rx_mode_work_enabled;
+
+	/* The lock to synchronize the access to refill_enabled */
+	spinlock_t rx_mode_lock;
+
 	/* Does the affinity hint is set for virtqueues? */
 	bool affinity_hint_set;
 
@@ -383,6 +392,22 @@ static void disable_delayed_refill(struct virtnet_info *vi)
 	spin_unlock_bh(&vi->refill_lock);
 }
 
+static void enable_rx_mode_work(struct virtnet_info *vi)
+{
+	spin_lock_bh(&vi->rx_mode_lock);
+	vi->rx_mode_work_enabled = true;
+	spin_unlock_bh(&vi->rx_mode_lock);
+}
+
+static void disable_rx_mode_work(struct virtnet_info *vi)
+{
+	spin_lock_bh(&vi->rx_mode_lock);
+	vi->rx_mode_work_enabled = false;
+	spin_unlock_bh(&vi->rx_mode_lock);
+
+	flush_work(&vi->rx_mode_work);
+}
+
 static void virtqueue_napi_schedule(struct napi_struct *napi,
 				    struct virtqueue *vq)
 {
@@ -1974,6 +1999,8 @@ static bool virtnet_send_command(struct virtnet_info *vi,
u8 class, u8 cmd,
 	/* Caller should know better */
 	BUG_ON(!virtio_has_feature(vi->vdev, VIRTIO_NET_F_CTRL_VQ));
 
+	ASSERT_RTNL();
+
 	vi->ctrl->status = ~0;
 	vi->ctrl->hdr.class = class;
 	vi->ctrl->hdr.cmd = cmd;
@@ -2160,9 +2187,11 @@ static int virtnet_close(struct net_device *dev)
 	return 0;
 }
 
-static void virtnet_set_rx_mode(struct net_device *dev)
+static void virtnet_rx_mode_work(struct work_struct *work)
 {
-	struct virtnet_info *vi = netdev_priv(dev);
+	struct virtnet_info *vi +		container_of(work, struct virtnet_info,
rx_mode_work);
+	struct net_device *dev = vi->dev;
 	struct scatterlist sg[2];
 	struct virtio_net_ctrl_mac *mac_data;
 	struct netdev_hw_addr *ha;
@@ -2175,8 +2204,12 @@ static void virtnet_set_rx_mode(struct net_device *dev)
 	if (!virtio_has_feature(vi->vdev, VIRTIO_NET_F_CTRL_RX))
 		return;
 
+	rtnl_lock();
+
+	netif_addr_lock_bh(dev);
 	vi->ctrl->promisc = ((dev->flags & IFF_PROMISC) != 0);
 	vi->ctrl->allmulti = ((dev->flags & IFF_ALLMULTI) != 0);
+	netif_addr_unlock_bh(dev);
 
 	sg_init_one(sg, &vi->ctrl->promisc,
sizeof(vi->ctrl->promisc));
 
@@ -2192,14 +2225,19 @@ static void virtnet_set_rx_mode(struct net_device *dev)
 		dev_warn(&dev->dev, "Failed to %sable allmulti mode.\n",
 			 vi->ctrl->allmulti ? "en" : "dis");
 
+	netif_addr_lock_bh(dev);
+
 	uc_count = netdev_uc_count(dev);
 	mc_count = netdev_mc_count(dev);
 	/* MAC filter - use one buffer for both lists */
 	buf = kzalloc(((uc_count + mc_count) * ETH_ALEN) +
 		      (2 * sizeof(mac_data->entries)), GFP_ATOMIC);
 	mac_data = buf;
-	if (!buf)
+	if (!buf) {
+		netif_addr_unlock_bh(dev);
+		rtnl_unlock();
 		return;
+	}
 
 	sg_init_table(sg, 2);
 
@@ -2220,6 +2258,8 @@ static void virtnet_set_rx_mode(struct net_device *dev)
 	netdev_for_each_mc_addr(ha, dev)
 		memcpy(&mac_data->macs[i++][0], ha->addr, ETH_ALEN);
 
+	netif_addr_unlock_bh(dev);
+
 	sg_set_buf(&sg[1], mac_data,
 		   sizeof(mac_data->entries) + (mc_count * ETH_ALEN));
 
@@ -2227,9 +2267,21 @@ static void virtnet_set_rx_mode(struct net_device *dev)
 				  VIRTIO_NET_CTRL_MAC_TABLE_SET, sg))
 		dev_warn(&dev->dev, "Failed to set MAC filter table.\n");
 
+	rtnl_unlock();
+
 	kfree(buf);
 }
 
+static void virtnet_set_rx_mode(struct net_device *dev)
+{
+	struct virtnet_info *vi = netdev_priv(dev);
+
+	spin_lock(&vi->rx_mode_lock);
+	if (vi->rx_mode_work_enabled)
+		schedule_work(&vi->rx_mode_work);
+	spin_unlock(&vi->rx_mode_lock);
+}
+
 static int virtnet_vlan_rx_add_vid(struct net_device *dev,
 				   __be16 proto, u16 vid)
 {
@@ -3000,6 +3052,7 @@ static void virtnet_freeze_down(struct virtio_device
*vdev)
 
 	/* Make sure no work handler is accessing the device */
 	flush_work(&vi->config_work);
+	disable_rx_mode_work(vi);
 
 	netif_tx_lock_bh(vi->dev);
 	netif_device_detach(vi->dev);
@@ -3022,6 +3075,8 @@ static int virtnet_restore_up(struct virtio_device *vdev)
 	virtio_device_ready(vdev);
 
 	enable_delayed_refill(vi);
+	enable_rx_mode_work(vi);
+	virtnet_set_rx_mode(vi->dev);
 
 	if (netif_running(vi->dev)) {
 		err = virtnet_open(vi->dev);
@@ -3799,7 +3854,9 @@ static int virtnet_probe(struct virtio_device *vdev)
 	vdev->priv = vi;
 
 	INIT_WORK(&vi->config_work, virtnet_config_changed_work);
+	INIT_WORK(&vi->rx_mode_work, virtnet_rx_mode_work);
 	spin_lock_init(&vi->refill_lock);
+	spin_lock_init(&vi->rx_mode_lock);
 
 	if (virtio_has_feature(vdev, VIRTIO_NET_F_MRG_RXBUF))
 		vi->mergeable_rx_bufs = true;
@@ -3905,6 +3962,8 @@ static int virtnet_probe(struct virtio_device *vdev)
 	if (vi->has_rss || vi->has_rss_hash_report)
 		virtnet_init_default_rss(vi);
 
+	enable_rx_mode_work(vi);
+
 	/* serialize netdev register + virtio_device_ready() with ndo_open() */
 	rtnl_lock();
 
@@ -3984,6 +4043,7 @@ static void virtnet_remove(struct virtio_device *vdev)
 
 	/* Make sure no work handler is accessing the device. */
 	flush_work(&vi->config_work);
+	disable_rx_mode_work(vi);
 
 	unregister_netdev(vi->dev);
 
-- 
2.25.1

Switch to reuse BAD_RING() to allow common logic to be implemented in
BAD_RING().

Signed-off-by: Jason Wang <jasowang at redhat.com>
---
Changes since V1:
- switch to use BAD_RING in virtio_break_device()
---
 drivers/virtio/virtio_ring.c | 8 ++++----
 1 file changed, 4 insertions(+), 4 deletions(-)

diff --git a/drivers/virtio/virtio_ring.c b/drivers/virtio/virtio_ring.c
index 2e7689bb933b..5cfb2fa8abee 100644
--- a/drivers/virtio/virtio_ring.c
+++ b/drivers/virtio/virtio_ring.c
@@ -58,7 +58,8 @@
 	do {							\
 		dev_err(&_vq->vq.vdev->dev,			\
 			"%s:"fmt, (_vq)->vq.name, ##args);	\
-		(_vq)->broken = true;				\
+		/* Pairs with READ_ONCE() in virtqueue_is_broken(). */ \
+		WRITE_ONCE((_vq)->broken, true);		       \
 	} while (0)
 #define START_USE(vq)
 #define END_USE(vq)
@@ -2237,7 +2238,7 @@ bool virtqueue_notify(struct virtqueue *_vq)
 
 	/* Prod other side to tell it about changes. */
 	if (!vq->notify(_vq)) {
-		vq->broken = true;
+		BAD_RING(vq, "vq %d is broken\n", vq->vq.index);
 		return false;
 	}
 	return true;
@@ -2786,8 +2787,7 @@ void virtio_break_device(struct virtio_device *dev)
 	list_for_each_entry(_vq, &dev->vqs, list) {
 		struct vring_virtqueue *vq = to_vvq(_vq);
 
-		/* Pairs with READ_ONCE() in virtqueue_is_broken(). */
-		WRITE_ONCE(vq->broken, true);
+		BAD_RING(vq, "Device break vq %d", _vq->index);
 	}
 	spin_unlock(&dev->vqs_list_lock);
 }
-- 
2.25.1

This patch introduces a per virtqueue waitqueue to allow driver to
sleep and wait for more used. Two new helpers are introduced to allow
driver to sleep and wake up.

Signed-off-by: Jason Wang <jasowang at redhat.com>
---
Changes since V1:
- check virtqueue_is_broken() as well
- use more_used() instead of virtqueue_get_buf() to allow caller to
  get buffers afterwards
---
 drivers/virtio/virtio_ring.c | 29 +++++++++++++++++++++++++++++
 include/linux/virtio.h       |  3 +++
 2 files changed, 32 insertions(+)

diff --git a/drivers/virtio/virtio_ring.c b/drivers/virtio/virtio_ring.c
index 5cfb2fa8abee..9c83eb945493 100644
--- a/drivers/virtio/virtio_ring.c
+++ b/drivers/virtio/virtio_ring.c
@@ -13,6 +13,7 @@
 #include <linux/dma-mapping.h>
 #include <linux/kmsan.h>
 #include <linux/spinlock.h>
+#include <linux/wait.h>
 #include <xen/xen.h>
 
 #ifdef DEBUG
@@ -60,6 +61,7 @@
 			"%s:"fmt, (_vq)->vq.name, ##args);	\
 		/* Pairs with READ_ONCE() in virtqueue_is_broken(). */ \
 		WRITE_ONCE((_vq)->broken, true);		       \
+		wake_up_interruptible(&(_vq)->wq);		       \
 	} while (0)
 #define START_USE(vq)
 #define END_USE(vq)
@@ -203,6 +205,9 @@ struct vring_virtqueue {
 	/* DMA, allocation, and size information */
 	bool we_own_ring;
 
+	/* Wait for buffer to be used */
+	wait_queue_head_t wq;
+
 #ifdef DEBUG
 	/* They're supposed to lock for us. */
 	unsigned int in_use;
@@ -2024,6 +2029,8 @@ static struct virtqueue *vring_create_virtqueue_packed(
 	if (virtio_has_feature(vdev, VIRTIO_F_ORDER_PLATFORM))
 		vq->weak_barriers = false;
 
+	init_waitqueue_head(&vq->wq);
+
 	err = vring_alloc_state_extra_packed(&vring_packed);
 	if (err)
 		goto err_state_extra;
@@ -2517,6 +2524,8 @@ static struct virtqueue *__vring_new_virtqueue(unsigned
int index,
 	if (virtio_has_feature(vdev, VIRTIO_F_ORDER_PLATFORM))
 		vq->weak_barriers = false;
 
+	init_waitqueue_head(&vq->wq);
+
 	err = vring_alloc_state_extra_split(vring_split);
 	if (err) {
 		kfree(vq);
@@ -2654,6 +2663,8 @@ static void vring_free(struct virtqueue *_vq)
 {
 	struct vring_virtqueue *vq = to_vvq(_vq);
 
+	wake_up_interruptible(&vq->wq);
+
 	if (vq->we_own_ring) {
 		if (vq->packed_ring) {
 			vring_free_queue(vq->vq.vdev,
@@ -2863,4 +2874,22 @@ const struct vring *virtqueue_get_vring(struct virtqueue
*vq)
 }
 EXPORT_SYMBOL_GPL(virtqueue_get_vring);
 
+int virtqueue_wait_for_used(struct virtqueue *_vq)
+{
+	struct vring_virtqueue *vq = to_vvq(_vq);
+
+	/* TODO: Tweak the timeout. */
+	return wait_event_interruptible_timeout(vq->wq,
+	       virtqueue_is_broken(_vq) || more_used(vq), HZ);
+}
+EXPORT_SYMBOL_GPL(virtqueue_wait_for_used);
+
+void virtqueue_wake_up(struct virtqueue *_vq)
+{
+	struct vring_virtqueue *vq = to_vvq(_vq);
+
+	wake_up_interruptible(&vq->wq);
+}
+EXPORT_SYMBOL_GPL(virtqueue_wake_up);
+
 MODULE_LICENSE("GPL");
diff --git a/include/linux/virtio.h b/include/linux/virtio.h
index dcab9c7e8784..2eb62c774895 100644
--- a/include/linux/virtio.h
+++ b/include/linux/virtio.h
@@ -72,6 +72,9 @@ void *virtqueue_get_buf(struct virtqueue *vq, unsigned int
*len);
 void *virtqueue_get_buf_ctx(struct virtqueue *vq, unsigned int *len,
 			    void **ctx);
 
+int virtqueue_wait_for_used(struct virtqueue *vq);
+void virtqueue_wake_up(struct virtqueue *vq);
+
 void virtqueue_disable_cb(struct virtqueue *vq);
 
 bool virtqueue_enable_cb(struct virtqueue *vq);
-- 
2.25.1

We used to busy waiting on the cvq command this tends to be
problematic since:

1) CPU could wait for ever on a buggy/malicous device
2) There's no wait to terminate the process that triggers the cvq
   command

So this patch switch to use virtqueue_wait_for_used() to sleep with a
timeout (1s) instead of busy polling for the cvq command forever. This
gives the scheduler a breath and can let the process can respond to
asignal. If the device doesn't respond in the timeout, break the
device.

Signed-off-by: Jason Wang <jasowang at redhat.com>
---
Changes since V1:
- break the device when timeout
- get buffer manually since the virtio core check more_used() instead
---
 drivers/net/virtio_net.c | 24 ++++++++++++++++--------
 1 file changed, 16 insertions(+), 8 deletions(-)

diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c
index efd9dd55828b..6a2ea64cfcb5 100644
--- a/drivers/net/virtio_net.c
+++ b/drivers/net/virtio_net.c
@@ -405,6 +405,7 @@ static void disable_rx_mode_work(struct virtnet_info *vi)
 	vi->rx_mode_work_enabled = false;
 	spin_unlock_bh(&vi->rx_mode_lock);
 
+	virtqueue_wake_up(vi->cvq);
 	flush_work(&vi->rx_mode_work);
 }
 
@@ -1497,6 +1498,11 @@ static bool try_fill_recv(struct virtnet_info *vi, struct
receive_queue *rq,
 	return !oom;
 }
 
+static void virtnet_cvq_done(struct virtqueue *cvq)
+{
+	virtqueue_wake_up(cvq);
+}
+
 static void skb_recv_done(struct virtqueue *rvq)
 {
 	struct virtnet_info *vi = rvq->vdev->priv;
@@ -1984,6 +1990,8 @@ static int virtnet_tx_resize(struct virtnet_info *vi,
 	return err;
 }
 
+static int virtnet_close(struct net_device *dev);
+
 /*
  * Send command via the control virtqueue and check status.  Commands
  * supported by the hypervisor, as indicated by feature bits, should
@@ -2026,14 +2034,14 @@ static bool virtnet_send_command(struct virtnet_info
*vi, u8 class, u8 cmd,
 	if (unlikely(!virtqueue_kick(vi->cvq)))
 		return vi->ctrl->status == VIRTIO_NET_OK;
 
-	/* Spin for a response, the kick causes an ioport write, trapping
-	 * into the hypervisor, so the request should be handled immediately.
-	 */
-	while (!virtqueue_get_buf(vi->cvq, &tmp) &&
-	       !virtqueue_is_broken(vi->cvq))
-		cpu_relax();
+	if (virtqueue_wait_for_used(vi->cvq)) {
+		virtqueue_get_buf(vi->cvq, &tmp);
+		return vi->ctrl->status == VIRTIO_NET_OK;
+	}
 
-	return vi->ctrl->status == VIRTIO_NET_OK;
+	netdev_err(vi->dev, "CVQ command timeout, break the virtio
device.");
+	virtio_break_device(vi->vdev);
+	return VIRTIO_NET_ERR;
 }
 
 static int virtnet_set_mac_address(struct net_device *dev, void *p)
@@ -3526,7 +3534,7 @@ static int virtnet_find_vqs(struct virtnet_info *vi)
 
 	/* Parameters for control virtqueue, if any */
 	if (vi->has_cvq) {
-		callbacks[total_vqs - 1] = NULL;
+		callbacks[total_vqs - 1] = virtnet_cvq_done;
 		names[total_vqs - 1] = "control";
 	}
 
-- 
2.25.1