From: Jason Wang <jasowang@redhat.com>
To: Ilya Maximets <i.maximets@samsung.com>,
Maxime Coquelin <maxime.coquelin@redhat.com>,
dev@dpdk.org, jfreimann@redhat.com, tiwei.bie@intel.com,
zhihong.wang@intel.com
Cc: stable@dpdk.org, "Michael S. Tsirkin" <mst@redhat.com>
Subject: Re: [dpdk-stable] [2/5] vhost: enforce desc flags and content read ordering
Date: Thu, 6 Dec 2018 12:24:48 +0800 [thread overview]
Message-ID: <b3156ec2-8514-a4ae-e526-f5bb2f1ac435@redhat.com> (raw)
In-Reply-To: <16a4b2fd-c701-7822-3215-62e431e3f339@samsung.com>
On 2018/12/5 下午9:33, Ilya Maximets wrote:
> On 05.12.2018 12:49, Maxime Coquelin wrote:
>> A read barrier is required to ensure that the ordering between
>> descriptor's flags and content reads is enforced.
>>
>> Fixes: 2f3225a7d69b ("vhost: add vector filling support for packed ring")
>> Cc: stable@dpdk.org
>>
>> Reported-by: Jason Wang <jasowang@redhat.com>
>> Signed-off-by: Maxime Coquelin <maxime.coquelin@redhat.com>
>> ---
>> lib/librte_vhost/virtio_net.c | 6 ++++++
>> 1 file changed, 6 insertions(+)
>>
>> diff --git a/lib/librte_vhost/virtio_net.c b/lib/librte_vhost/virtio_net.c
>> index f11ebb54f..68b72e7a5 100644
>> --- a/lib/librte_vhost/virtio_net.c
>> +++ b/lib/librte_vhost/virtio_net.c
>> @@ -520,6 +520,12 @@ fill_vec_buf_packed(struct virtio_net *dev, struct vhost_virtqueue *vq,
>> if (unlikely(!desc_is_avail(&descs[avail_idx], wrap_counter)))
>> return -1;
>>
>> + /*
>> + * The ordering between desc flags and desc
>> + * content reads need to be enforced.
>> + */
>> + rte_smp_rmb();
>> +
> Same here. 'desc_is_avail' reads and uses the flags. i.e.
> no way for reordering,
> Writes must be ordered on the virtio side by the write barrier.
> This means that if flags are updated (desc_is_avail() == true)
> than the whole descriptor already updated and the data is written.
> No need to have any read barriers here.
In fact , the sequence might be:
flag = read desc[avail_idx].flag [1]
if(flag is not avail) {
read desc[avail_idx].id [2]
}
There's no data dependency but control dependency here, so 2 could be
done before 1 without a rmb.
Thanks
>
>> *desc_count = 0;
>> *len = 0;
>>
>>
next prev parent reply other threads:[~2018-12-06 4:25 UTC|newest]
Thread overview: 14+ messages / expand[flat|nested] mbox.gz Atom feed top
[not found] <20181205094957.1938-1-maxime.coquelin@redhat.com>
2018-12-05 9:49 ` [dpdk-stable] [PATCH 1/5] vhost: enforce avail index and desc " Maxime Coquelin
[not found] ` <CGME20181205113041eucas1p1943b9c13af2fb5b736ba4906b59a9cd5@eucas1p1.samsung.com>
2018-12-05 11:30 ` [dpdk-stable] [1/5] " Ilya Maximets
2018-12-06 4:17 ` Jason Wang
2018-12-06 12:48 ` Ilya Maximets
2018-12-06 13:25 ` Jason Wang
2018-12-06 13:48 ` Michael S. Tsirkin
2018-12-07 14:58 ` Ilya Maximets
2018-12-07 15:44 ` Michael S. Tsirkin
[not found] ` <CGME20181211103848eucas1p10c270ca8997fea8a2f55c2d94d02baea@eucas1p1.samsung.com>
2018-12-11 10:38 ` Ilya Maximets
2018-12-11 14:46 ` Maxime Coquelin
2018-12-05 9:49 ` [dpdk-stable] [PATCH 2/5] vhost: enforce desc flags and content " Maxime Coquelin
[not found] ` <CGME20181205133332eucas1p195b3864ed146403e314d7004d27be285@eucas1p1.samsung.com>
2018-12-05 13:33 ` [dpdk-stable] [2/5] " Ilya Maximets
2018-12-06 4:24 ` Jason Wang [this message]
2018-12-06 11:34 ` Ilya Maximets
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=b3156ec2-8514-a4ae-e526-f5bb2f1ac435@redhat.com \
--to=jasowang@redhat.com \
--cc=dev@dpdk.org \
--cc=i.maximets@samsung.com \
--cc=jfreimann@redhat.com \
--cc=maxime.coquelin@redhat.com \
--cc=mst@redhat.com \
--cc=stable@dpdk.org \
--cc=tiwei.bie@intel.com \
--cc=zhihong.wang@intel.com \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).