On 2015/4/23 0:33, Huawei Xie wrote: > update of used->idx and read of avail->flags could be reordered. > memory fence should be used to ensure the order, otherwise guest could see a > stale used->idx value after it toggles the interrupt suppression flag. > > Signed-off-by: Huawei Xie <huawei.xie at intel.com> > --- > lib/librte_vhost/vhost_rxtx.c | 3 +++ > 1 file changed, 3 insertions(+) > > diff --git a/lib/librte_vhost/vhost_rxtx.c b/lib/librte_vhost/vhost_rxtx.c > index 510ffe8..6afba35 100644 > --- a/lib/librte_vhost/vhost_rxtx.c > +++ b/lib/librte_vhost/vhost_rxtx.c > @@ -178,6 +178,9 @@ virtio_dev_rx(struct virtio_net *dev, uint16_t queue_id, > *(volatile uint16_t *)&vq->used->idx += count; > vq->last_used_idx = res_end_idx; > > + /* flush used->idx update before we read avail->flags. */ > + rte_mb(); > + > /* Kick the guest if necessary. */ > if (!(vq->avail->flags & VRING_AVAIL_F_NO_INTERRUPT)) > eventfd_write((int)vq->callfd, 1); >
If not add memory fence what would happen? Packets loss or interrupt loss?How to test it ?
