* [dpdk-stable] [PATCH v3 1/3] net/virtio: add missing barrier before reading the flags
[not found] ` <CGME20190109145027eucas1p2437215de0df4c691eb84d4e84bfc71e5@eucas1p2.samsung.com>
@ 2019-01-09 14:50 ` Ilya Maximets
2019-01-10 14:31 ` Maxime Coquelin
0 siblings, 1 reply; 2+ messages in thread
From: Ilya Maximets @ 2019-01-09 14:50 UTC (permalink / raw)
To: dev, Maxime Coquelin, Michael S . Tsirkin, Xiao Wang
Cc: Tiwei Bie, Zhihong Wang, jfreimann, Jason Wang, xiaolong.ye,
alejandro.lucero, Ilya Maximets, stable
Reading the used->flags could be reordered with avail->idx update.
vhost in kernel disables notifications for the time of packets
receiving, like this:
1. disable notify
2. process packets
3. enable notify
4. has more packets ? goto 1
In case of reordering, virtio driver could read the flags on
step 2 while notifications disabled and update avail->idx after
the step 4, i.e. vhost will exit the loop on step 4 with
notifications enabled, but virtio will not notify.
Fixes: c1f86306a026 ("virtio: add new driver")
CC: stable@dpdk.org
Reported-by: Shahaf Shuler <shahafs@mellanox.com>
Signed-off-by: Ilya Maximets <i.maximets@samsung.com>
---
drivers/net/virtio/virtqueue.h | 8 ++++++++
1 file changed, 8 insertions(+)
diff --git a/drivers/net/virtio/virtqueue.h b/drivers/net/virtio/virtqueue.h
index d8ae5cdec..dffa03669 100644
--- a/drivers/net/virtio/virtqueue.h
+++ b/drivers/net/virtio/virtqueue.h
@@ -415,6 +415,11 @@ vq_update_avail_ring(struct virtqueue *vq, uint16_t desc_idx)
static inline int
virtqueue_kick_prepare(struct virtqueue *vq)
{
+ /*
+ * Ensure updated avail->idx is visible to vhost before reading
+ * the used->flags.
+ */
+ virtio_mb();
return !(vq->vq_ring.used->flags & VRING_USED_F_NO_NOTIFY);
}
@@ -423,6 +428,9 @@ virtqueue_kick_prepare_packed(struct virtqueue *vq)
{
uint16_t flags;
+ /*
+ * Ensure updated data is visible to vhost before reading the flags.
+ */
virtio_mb();
flags = vq->ring_packed.device_event->desc_event_flags;
--
2.17.1
^ permalink raw reply [flat|nested] 2+ messages in thread
* Re: [dpdk-stable] [PATCH v3 1/3] net/virtio: add missing barrier before reading the flags
2019-01-09 14:50 ` [dpdk-stable] [PATCH v3 1/3] net/virtio: add missing barrier before reading the flags Ilya Maximets
@ 2019-01-10 14:31 ` Maxime Coquelin
0 siblings, 0 replies; 2+ messages in thread
From: Maxime Coquelin @ 2019-01-10 14:31 UTC (permalink / raw)
To: Ilya Maximets, dev, Michael S . Tsirkin, Xiao Wang
Cc: Tiwei Bie, Zhihong Wang, jfreimann, Jason Wang, xiaolong.ye,
alejandro.lucero, stable
On 1/9/19 3:50 PM, Ilya Maximets wrote:
> Reading the used->flags could be reordered with avail->idx update.
> vhost in kernel disables notifications for the time of packets
> receiving, like this:
>
> 1. disable notify
> 2. process packets
> 3. enable notify
> 4. has more packets ? goto 1
>
> In case of reordering, virtio driver could read the flags on
> step 2 while notifications disabled and update avail->idx after
> the step 4, i.e. vhost will exit the loop on step 4 with
> notifications enabled, but virtio will not notify.
>
> Fixes: c1f86306a026 ("virtio: add new driver")
> CC: stable@dpdk.org
>
> Reported-by: Shahaf Shuler <shahafs@mellanox.com>
> Signed-off-by: Ilya Maximets <i.maximets@samsung.com>
> ---
> drivers/net/virtio/virtqueue.h | 8 ++++++++
> 1 file changed, 8 insertions(+)
>
Reviewed-by: Maxime Coquelin <maxime.coquelin@redhat.com>
Thanks,
Maxime
^ permalink raw reply [flat|nested] 2+ messages in thread
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2019-01-09 14:50 ` [dpdk-stable] [PATCH v3 1/3] net/virtio: add missing barrier before reading the flags Ilya Maximets
2019-01-10 14:31 ` Maxime Coquelin
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