On Tue, 11 Oct 2022 18:44:28 +0200
Maxime Coquelin <maxime.coque...@redhat.com> wrote:
> On 9/12/22 05:36, Kangjie Xu wrote:
> > We change the behavior of vhost_user_get_vring_base(). Previosly,
> > destroying a virtqueue will cause the whole device to be destroyed.
> > The behavior is not specified in the vhost-user protocol.
> >
> > Thus, we refactor this part. The device will be destroyed only when
> > all virtqueues in the device are going to be destroyed.
> >
> > This helps us to simplify the implementation when resetting a virtqueue.
> >
> > Signed-off-by: Kangjie Xu <kangjie...@linux.alibaba.com>
> > Signed-off-by: Xuan Zhuo <xuanz...@linux.alibaba.com>
> > ---
> > lib/vhost/vhost_user.c | 10 ++++++++--
> > 1 file changed, 8 insertions(+), 2 deletions(-)
> >
> > diff --git a/lib/vhost/vhost_user.c b/lib/vhost/vhost_user.c
> > index 4ad28bac45..a9f0709f94 100644
> > --- a/lib/vhost/vhost_user.c
> > +++ b/lib/vhost/vhost_user.c
> > @@ -2088,10 +2088,16 @@ vhost_user_get_vring_base(struct virtio_net **pdev,
> > {
> > struct virtio_net *dev = *pdev;
> > struct vhost_virtqueue *vq =
> > dev->virtqueue[ctx->msg.payload.state.index];
> > + uint32_t i, num_live_vring = 0;
> > uint64_t val;
> >
> > - /* We have to stop the queue (virtio) if it is running. */
> > - vhost_destroy_device_notify(dev);
> > + /* Stop the device when vq is the last active queue */
> > + for (i = 0; i < dev->nr_vring; i++)
> > + if (dev->virtqueue[i]->access_ok)
> > + num_live_vring++;
> > +
> > + if (num_live_vring == 1 && vq->access_ok)
> > + vhost_destroy_device_notify(dev);
> >
> > dev->flags &= ~VIRTIO_DEV_READY;
> > dev->flags &= ~VIRTIO_DEV_VDPA_CONFIGURED;
>
> I think we are missing something here.
>
> We used to send the device destroy notification before getting the ring
> indexes, in order to ensure that the application has stopped processing
> the rings.
>
> With this patch, the application may still be polling the ring while we
> get the ring indexes (e.g. a thread in the application may be in the
> middle of rte_vhost_dequeue_burst() on that ring). So at best the ring
> indexes returned to the Vhost-user master will be outdated. At worst, it
> will crash the application because we call vring_invalidate() without
> the vq's lock being taken.
>
> I think you should protect all the VQ indexes fetching and VQ deinit
> using its access_lock.
>
> Maxime
>
Please address Maxime's feedback.
