From mboxrd@z Thu Jan 1 00:00:00 1970 From: "Michael S. Tsirkin" Subject: Re: [PATCH net V2 1/4] vhost: make sure used idx is seen before log in vhost_add_used_n() Date: Wed, 12 Dec 2018 09:33:37 -0500 Message-ID: <20181212093303-mutt-send-email-mst@kernel.org> References: <20181212100819.21295-1-jasowang@redhat.com> <20181212100819.21295-2-jasowang@redhat.com> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Cc: kvm@vger.kernel.org, virtualization@lists.linux-foundation.org, netdev@vger.kernel.org, linux-kernel@vger.kernel.org To: Jason Wang Return-path: Content-Disposition: inline In-Reply-To: <20181212100819.21295-2-jasowang@redhat.com> Sender: linux-kernel-owner@vger.kernel.org List-Id: netdev.vger.kernel.org On Wed, Dec 12, 2018 at 06:08:16PM +0800, Jason Wang wrote: > We miss a write barrier that guarantees used idx is updated and seen > before log. This will let userspace sync and copy used ring before > used idx is update. Fix this by adding a barrier before log_write(). > > Fixes: 8dd014adfea6f ("vhost-net: mergeable buffers support") > Signed-off-by: Jason Wang Acked-by: Michael S. Tsirkin also for 4.20 and seems like a stable candidate. > --- > drivers/vhost/vhost.c | 2 ++ > 1 file changed, 2 insertions(+) > > diff --git a/drivers/vhost/vhost.c b/drivers/vhost/vhost.c > index 6b98d8e3a5bf..5915f240275a 100644 > --- a/drivers/vhost/vhost.c > +++ b/drivers/vhost/vhost.c > @@ -2220,6 +2220,8 @@ int vhost_add_used_n(struct vhost_virtqueue *vq, struct vring_used_elem *heads, > return -EFAULT; > } > if (unlikely(vq->log_used)) { > + /* Make sure used idx is seen before log. */ > + smp_wmb(); > /* Log used index update. */ > log_write(vq->log_base, > vq->log_addr + offsetof(struct vring_used, idx), > -- > 2.17.1