DPDK patches and discussions
 help / color / mirror / Atom feed
From: Ilya Maximets <i.maximets@samsung.com>
To: Maxime Coquelin <maxime.coquelin@redhat.com>,
	dev@dpdk.org, jfreimann@redhat.com, tiwei.bie@intel.com,
	zhihong.wang@intel.com, jasowang@redhat.com
Cc: stable@dpdk.org
Subject: Re: [dpdk-dev] [2/5] vhost: enforce desc flags and content read ordering
Date: Wed, 5 Dec 2018 16:33:31 +0300	[thread overview]
Message-ID: <16a4b2fd-c701-7822-3215-62e431e3f339@samsung.com> (raw)
In-Reply-To: <20181205094957.1938-3-maxime.coquelin@redhat.com>

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.

>  	*desc_count = 0;
>  	*len = 0;
>  
> 

  parent reply	other threads:[~2018-12-05 13:33 UTC|newest]

Thread overview: 21+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2018-12-05  9:49 [dpdk-dev] [PATCH 0/5] vhost: add missing barriers, remove useless volatiles Maxime Coquelin
2018-12-05  9:49 ` [dpdk-dev] [PATCH 1/5] vhost: enforce avail index and desc read ordering Maxime Coquelin
     [not found]   ` <CGME20181205113041eucas1p1943b9c13af2fb5b736ba4906b59a9cd5@eucas1p1.samsung.com>
2018-12-05 11:30     ` [dpdk-dev] [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-dev] [PATCH 2/5] vhost: enforce desc flags and content " Maxime Coquelin
     [not found]   ` <CGME20181205133332eucas1p195b3864ed146403e314d7004d27be285@eucas1p1.samsung.com>
2018-12-05 13:33     ` Ilya Maximets [this message]
2018-12-06  4:24       ` [dpdk-dev] [2/5] " Jason Wang
2018-12-06 11:34         ` Ilya Maximets
2018-12-05  9:49 ` [dpdk-dev] [PATCH 3/5] vhost: prefetch descriptor after the read barrier Maxime Coquelin
2018-12-05  9:49 ` [dpdk-dev] [PATCH 4/5] vhost: remove useless prefetch for packed ring descriptor Maxime Coquelin
2018-12-05  9:49 ` [dpdk-dev] [PATCH 5/5] vhost: remove useless casts to volatile Maxime Coquelin
     [not found]   ` <CGME20181205135231eucas1p1c89281f6525a0fedab4a2fc0d2e21393@eucas1p1.samsung.com>
2018-12-05 13:52     ` [dpdk-dev] [5/5] " Ilya Maximets
2018-12-06 16:59       ` Maxime Coquelin
2018-12-07 11:16         ` 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=16a4b2fd-c701-7822-3215-62e431e3f339@samsung.com \
    --to=i.maximets@samsung.com \
    --cc=dev@dpdk.org \
    --cc=jasowang@redhat.com \
    --cc=jfreimann@redhat.com \
    --cc=maxime.coquelin@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).