[dpdk-dev] [PATCH v5] vhost_user: protect active rings from async ring changes

[Victor Kaplansky]

When performing live migration or memory hot-plugging,
the changes to the device and vrings made by message handler
done independently from vring usage by PMD threads.

This causes for example segfaults during live-migration
with MQ enable, but in general virtually any request
sent by qemu changing the state of device can cause
problems.

These patches fixes all above issues by adding a spinlock
to every vring and requiring message handler to start operation
only after ensuring that all PMD threads related to the device
are out of critical section accessing the vring data.

Each vring has its own lock in order to not create contention
between PMD threads of different vrings and to prevent
performance degradation by scaling queue pair number.

See https://bugzilla.redhat.com/show_bug.cgi?id=1450680

Signed-off-by: Victor Kaplansky <victork at redhat.com>
---
v5:
 o get rid of spinlock wrapping functions in vhost.h

v4:

 o moved access_unlock before accessing enable flag and
   access_unlock after iommu_unlock consistently.
 o cosmetics: removed blank line.
 o the access_lock variable moved to be in the same
   cache line with enable and access_ok flags.
 o dequeue path is now guarded with trylock and returning
   zero if unsuccessful.
 o GET_VRING_BASE operation is not guarded by access lock
   to avoid deadlock with device_destroy. See the comment
   in the code.
 o Fixed error path exit from enqueue and dequeue carefully
   unlocking access and iommu locks as appropriate.

v3:
   o Added locking to enqueue flow.
   o Enqueue path guarded as well as dequeue path.
   o Changed name of active_lock.
   o Added initialization of guarding spinlock.
   o Reworked functions skimming over all virt-queues.
   o Performance measurements done by Maxime Coquelin shows
     no degradation in bandwidth and throughput.
   o Spelling.
   o Taking lock only on set operations.
   o IOMMU messages are not guarded by access lock.

v2:
   o Fixed checkpatch complains.
   o Added Signed-off-by.
   o Refined placement of guard to exclude IOMMU messages.
   o TODO: performance degradation measurement.

 lib/librte_vhost/vhost.h      |  6 ++--
 lib/librte_vhost/vhost.c      |  1 +
 lib/librte_vhost/vhost_user.c | 70 +++++++++++++++++++++++++++++++++++++++++++
 lib/librte_vhost/virtio_net.c | 28 ++++++++++++++---
 4 files changed, 99 insertions(+), 6 deletions(-)

diff --git a/lib/librte_vhost/vhost.h b/lib/librte_vhost/vhost.h
index 1cc81c17..c8f2a817 100644
--- a/lib/librte_vhost/vhost.h
+++ b/lib/librte_vhost/vhost.h
@@ -108,12 +108,14 @@ struct vhost_virtqueue {
 
 	/* Backend value to determine if device should started/stopped */
 	int			backend;
+	int			enabled;
+	int			access_ok;
+	rte_spinlock_t		access_lock;
+
 	/* Used to notify the guest (trigger interrupt) */
 	int			callfd;
 	/* Currently unused as polling mode is enabled */
 	int			kickfd;
-	int			enabled;
-	int			access_ok;
 
 	/* Physical address of used ring, for logging */
 	uint64_t		log_guest_addr;
diff --git a/lib/librte_vhost/vhost.c b/lib/librte_vhost/vhost.c
index 4f8b73a0..dcc42fc7 100644
--- a/lib/librte_vhost/vhost.c
+++ b/lib/librte_vhost/vhost.c
@@ -259,6 +259,7 @@ alloc_vring_queue(struct virtio_net *dev, uint32_t vring_idx)
 
 	dev->virtqueue[vring_idx] = vq;
 	init_vring_queue(dev, vring_idx);
+	rte_spinlock_init(&vq->access_lock);
 
 	dev->nr_vring += 1;
 
diff --git a/lib/librte_vhost/vhost_user.c b/lib/librte_vhost/vhost_user.c
index f4c7ce46..0685d4e7 100644
--- a/lib/librte_vhost/vhost_user.c
+++ b/lib/librte_vhost/vhost_user.c
@@ -1190,12 +1190,47 @@ vhost_user_check_and_alloc_queue_pair(struct virtio_net *dev, VhostUserMsg *msg)
 	return alloc_vring_queue(dev, vring_idx);
 }
 
+static void
+vhost_user_lock_all_queue_pairs(struct virtio_net *dev)
+{
+	unsigned int i = 0;
+	unsigned int vq_num = 0;
+
+	while (vq_num < dev->nr_vring) {
+		struct vhost_virtqueue *vq = dev->virtqueue[i];
+
+		if (vq) {
+			rte_spinlock_lock(&vq->access_lock);
+			vq_num++;
+		}
+		i++;
+	}
+}
+
+static void
+vhost_user_unlock_all_queue_pairs(struct virtio_net *dev)
+{
+	unsigned int i = 0;
+	unsigned int vq_num = 0;
+
+	while (vq_num < dev->nr_vring) {
+		struct vhost_virtqueue *vq = dev->virtqueue[i];
+
+		if (vq) {
+			rte_spinlock_unlock(&vq->access_lock);
+			vq_num++;
+		}
+		i++;
+	}
+}
+
 int
 vhost_user_msg_handler(int vid, int fd)
 {
 	struct virtio_net *dev;
 	struct VhostUserMsg msg;
 	int ret;
+	int unlock_required = 0;
 
 	dev = get_device(vid);
 	if (dev == NULL)
@@ -1241,6 +1276,38 @@ vhost_user_msg_handler(int vid, int fd)
 		return -1;
 	}
 
+	/*
+	 * Note: we don't lock all queues on VHOST_USER_GET_VRING_BASE,
+	 * since it is sent when virtio stops and device is destroyed.
+	 * destroy_device waits for queues to be inactive, so it is safe.
+	 * Otherwise taking the access_lock would cause a dead lock.
+	 */
+	switch (msg.request.master) {
+	case VHOST_USER_SET_FEATURES:
+	case VHOST_USER_SET_PROTOCOL_FEATURES:
+	case VHOST_USER_SET_OWNER:
+	case VHOST_USER_RESET_OWNER:
+	case VHOST_USER_SET_MEM_TABLE:
+	case VHOST_USER_SET_LOG_BASE:
+	case VHOST_USER_SET_LOG_FD:
+	case VHOST_USER_SET_VRING_NUM:
+	case VHOST_USER_SET_VRING_ADDR:
+	case VHOST_USER_SET_VRING_BASE:
+	case VHOST_USER_SET_VRING_KICK:
+	case VHOST_USER_SET_VRING_CALL:
+	case VHOST_USER_SET_VRING_ERR:
+	case VHOST_USER_SET_VRING_ENABLE:
+	case VHOST_USER_SEND_RARP:
+	case VHOST_USER_NET_SET_MTU:
+	case VHOST_USER_SET_SLAVE_REQ_FD:
+		vhost_user_lock_all_queue_pairs(dev);
+		unlock_required = 1;
+		break;
+	default:
+		break;
+
+	}
+
 	switch (msg.request.master) {
 	case VHOST_USER_GET_FEATURES:
 		msg.payload.u64 = vhost_user_get_features(dev);
@@ -1342,6 +1409,9 @@ vhost_user_msg_handler(int vid, int fd)
 
 	}
 
+	if (unlock_required)
+		vhost_user_unlock_all_queue_pairs(dev);
+
 	if (msg.flags & VHOST_USER_NEED_REPLY) {
 		msg.payload.u64 = !!ret;
 		msg.size = sizeof(msg.payload.u64);
diff --git a/lib/librte_vhost/virtio_net.c b/lib/librte_vhost/virtio_net.c
index 6fee16e5..e09a927d 100644
--- a/lib/librte_vhost/virtio_net.c
+++ b/lib/librte_vhost/virtio_net.c
@@ -44,6 +44,7 @@
 #include <rte_udp.h>
 #include <rte_sctp.h>
 #include <rte_arp.h>
+#include <rte_spinlock.h>
 
 #include "iotlb.h"
 #include "vhost.h"
@@ -326,8 +327,11 @@ virtio_dev_rx(struct virtio_net *dev, uint16_t queue_id,
 	}
 
 	vq = dev->virtqueue[queue_id];
+
+	rte_spinlock_lock(&vq->access_lock);
+
 	if (unlikely(vq->enabled == 0))
-		return 0;
+		goto out_access_unlock;
 
 	if (dev->features & (1ULL << VIRTIO_F_IOMMU_PLATFORM))
 		vhost_user_iotlb_rd_lock(vq);
@@ -419,6 +423,9 @@ virtio_dev_rx(struct virtio_net *dev, uint16_t queue_id,
 	if (dev->features & (1ULL << VIRTIO_F_IOMMU_PLATFORM))
 		vhost_user_iotlb_rd_unlock(vq);
 
+out_access_unlock:
+	rte_spinlock_unlock(&vq->access_lock);
+
 	return count;
 }
 
@@ -651,8 +658,11 @@ virtio_dev_merge_rx(struct virtio_net *dev, uint16_t queue_id,
 	}
 
 	vq = dev->virtqueue[queue_id];
+
+	rte_spinlock_lock(&vq->access_lock);
+
 	if (unlikely(vq->enabled == 0))
-		return 0;
+		goto out_access_unlock;
 
 	if (dev->features & (1ULL << VIRTIO_F_IOMMU_PLATFORM))
 		vhost_user_iotlb_rd_lock(vq);
@@ -715,6 +725,9 @@ virtio_dev_merge_rx(struct virtio_net *dev, uint16_t queue_id,
 	if (dev->features & (1ULL << VIRTIO_F_IOMMU_PLATFORM))
 		vhost_user_iotlb_rd_unlock(vq);
 
+out_access_unlock:
+	rte_spinlock_unlock(&vq->access_lock);
+
 	return pkt_idx;
 }
 
@@ -1180,9 +1193,13 @@ rte_vhost_dequeue_burst(int vid, uint16_t queue_id,
 	}
 
 	vq = dev->virtqueue[queue_id];
-	if (unlikely(vq->enabled == 0))
+
+	if (unlikely(rte_spinlock_trylock(&vq->access_lock) == 0))
 		return 0;
 
+	if (unlikely(vq->enabled == 0))
+		goto out_access_unlock;
+
 	vq->batch_copy_nb_elems = 0;
 
 	if (dev->features & (1ULL << VIRTIO_F_IOMMU_PLATFORM))
@@ -1240,7 +1257,7 @@ rte_vhost_dequeue_burst(int vid, uint16_t queue_id,
 		if (rarp_mbuf == NULL) {
 			RTE_LOG(ERR, VHOST_DATA,
 				"Failed to allocate memory for mbuf.\n");
-			return 0;
+			goto out;
 		}
 
 		if (make_rarp_packet(rarp_mbuf, &dev->mac)) {
@@ -1356,6 +1373,9 @@ rte_vhost_dequeue_burst(int vid, uint16_t queue_id,
 	if (dev->features & (1ULL << VIRTIO_F_IOMMU_PLATFORM))
 		vhost_user_iotlb_rd_unlock(vq);
 
+out_access_unlock:
+	rte_spinlock_unlock(&vq->access_lock);
+
 	if (unlikely(rarp_mbuf != NULL)) {
 		/*
 		 * Inject it to the head of "pkts" array, so that switch's mac
-- 
Victor