diff options
Diffstat (limited to 'drivers/vhost/vhost.c')
| -rw-r--r-- | drivers/vhost/vhost.c | 28 |
1 files changed, 22 insertions, 6 deletions
diff --git a/drivers/vhost/vhost.c b/drivers/vhost/vhost.c index 2f58181b918d..c0f81e8cb50c 100644 --- a/drivers/vhost/vhost.c +++ b/drivers/vhost/vhost.c @@ -290,6 +290,7 @@ static void vhost_vq_reset(struct vhost_dev *dev, vq->avail = NULL; vq->used = NULL; vq->last_avail_idx = 0; + vq->last_used_event = 0; vq->avail_idx = 0; vq->last_used_idx = 0; vq->signalled_used = 0; @@ -1324,7 +1325,7 @@ long vhost_vring_ioctl(struct vhost_dev *d, int ioctl, void __user *argp) r = -EINVAL; break; } - vq->last_avail_idx = s.num; + vq->last_avail_idx = vq->last_used_event = s.num; /* Forget the cached index value. */ vq->avail_idx = vq->last_avail_idx; break; @@ -2159,10 +2160,6 @@ static bool vhost_notify(struct vhost_dev *dev, struct vhost_virtqueue *vq) __u16 old, new; __virtio16 event; bool v; - /* Flush out used index updates. This is paired - * with the barrier that the Guest executes when enabling - * interrupts. */ - smp_mb(); if (vhost_has_feature(vq, VIRTIO_F_NOTIFY_ON_EMPTY) && unlikely(vq->avail_idx == vq->last_avail_idx)) @@ -2170,6 +2167,10 @@ static bool vhost_notify(struct vhost_dev *dev, struct vhost_virtqueue *vq) if (!vhost_has_feature(vq, VIRTIO_RING_F_EVENT_IDX)) { __virtio16 flags; + /* Flush out used index updates. This is paired + * with the barrier that the Guest executes when enabling + * interrupts. */ + smp_mb(); if (vhost_get_user(vq, flags, &vq->avail->flags)) { vq_err(vq, "Failed to get flags"); return true; @@ -2184,11 +2185,26 @@ static bool vhost_notify(struct vhost_dev *dev, struct vhost_virtqueue *vq) if (unlikely(!v)) return true; + /* We're sure if the following conditions are met, there's no + * need to notify guest: + * 1) cached used event is ahead of new + * 2) old to new updating does not cross cached used event. */ + if (vring_need_event(vq->last_used_event, new + vq->num, new) && + !vring_need_event(vq->last_used_event, new, old)) + return false; + + /* Flush out used index updates. This is paired + * with the barrier that the Guest executes when enabling + * interrupts. */ + smp_mb(); + if (vhost_get_user(vq, event, vhost_used_event(vq))) { vq_err(vq, "Failed to get used event idx"); return true; } - return vring_need_event(vhost16_to_cpu(vq, event), new, old); + vq->last_used_event = vhost16_to_cpu(vq, event); + + return vring_need_event(vq->last_used_event, new, old); } /* This actually signals the guest, using eventfd. */ |