Make sense, Thanks. Cheers JJ
> -----Original Message----- > From: Maxime Coquelin [mailto:maxime.coque...@redhat.com] > Sent: Wednesday, January 31, 2018 4:13 PM > To: Chen, Junjie J <junjie.j.c...@intel.com>; Victor Kaplansky > <vict...@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 <vict...@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
