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

["Chen, Junjie J" <junjie.j.chen@intel.com>]

Make sense, Thanks.

Cheers
JJ


> -----Original Message-----
> From: Maxime Coquelin [mailto:maxime.coquelin@redhat.com]
> Sent: Wednesday, January 31, 2018 4:13 PM
> To: Chen, Junjie J <junjie.j.chen@intel.com>; Victor Kaplansky
> <victork@redhat.com>
> Cc: dev@dpdk.org
> Subject: Re: [dpdk-dev] [PATCH v5] vhost_user: protect active rings from
> async ring changes
> 
> Hi,
> 
> On 01/31/2018 07:51 AM, Chen, Junjie J wrote:
> > Hi
> > May I know why not use trylock also in enqueue path?
> 
> Because if rte_vhost_enqueue_burst() returns 0, the caller is likely to drop
> the packets. This is what happens for example with OVS:
> 
> static void
> __netdev_dpdk_vhost_send(struct netdev *netdev, int qid,
>                           struct dp_packet **pkts, int cnt) { ...
>      do {
>          int vhost_qid = qid * VIRTIO_QNUM + VIRTIO_RXQ;
>          unsigned int tx_pkts;
> 
>          tx_pkts = rte_vhost_enqueue_burst(vid, vhost_qid, cur_pkts, cnt);
>          if (OVS_LIKELY(tx_pkts)) {
>              /* Packets have been sent.*/
>              cnt -= tx_pkts;
>              /* Prepare for possible retry.*/
>              cur_pkts = &cur_pkts[tx_pkts];
>          } else {
>              /* No packets sent - do not retry.*/
>              break;
>          }
>      } while (cnt && (retries++ <= VHOST_ENQ_RETRY_NUM)); ...
> 
> 
> Maxime
> > Cheers
> > JJ
> >
> >>
> >> 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@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