On Thu, Dec 22, 2022 at 5:19 PM Eugenio Perez Martin
<eperezma@xxxxxxxxxx> wrote:
>
> On Thu, Dec 22, 2022 at 7:05 AM Jason Wang <jasowang@xxxxxxxxxx> wrote:
> >
> > We used to busy waiting on the cvq command this tends to be
> > problematic since:
> >
> > 1) CPU could wait for ever on a buggy/malicous device
> > 2) There's no wait to terminate the process that triggers the cvq
> > command
> >
> > So this patch switch to use sleep with a timeout (1s) instead of busy
> > polling for the cvq command forever. This gives the scheduler a breath
> > and can let the process can respond to a signal.
> >
> > Signed-off-by: Jason Wang <jasowang@xxxxxxxxxx>
> > ---
> > drivers/net/virtio_net.c | 15 ++++++++-------
> > 1 file changed, 8 insertions(+), 7 deletions(-)
> >
> > diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c
> > index 8225496ccb1e..69173049371f 100644
> > --- a/drivers/net/virtio_net.c
> > +++ b/drivers/net/virtio_net.c
> > @@ -405,6 +405,7 @@ static void disable_rx_mode_work(struct virtnet_info *vi)
> > vi->rx_mode_work_enabled = false;
> > spin_unlock_bh(&vi->rx_mode_lock);
> >
> > + virtqueue_wake_up(vi->cvq);
> > flush_work(&vi->rx_mode_work);
> > }
> >
> > @@ -1497,6 +1498,11 @@ static bool try_fill_recv(struct virtnet_info *vi, struct receive_queue *rq,
> > return !oom;
> > }
> >
> > +static void virtnet_cvq_done(struct virtqueue *cvq)
> > +{
> > + virtqueue_wake_up(cvq);
> > +}
> > +
> > static void skb_recv_done(struct virtqueue *rvq)
> > {
> > struct virtnet_info *vi = rvq->vdev->priv;
> > @@ -2024,12 +2030,7 @@ static bool virtnet_send_command(struct virtnet_info *vi, u8 class, u8 cmd,
> > if (unlikely(!virtqueue_kick(vi->cvq)))
> > return vi->ctrl->status == VIRTIO_NET_OK;
> >
> > - /* Spin for a response, the kick causes an ioport write, trapping
> > - * into the hypervisor, so the request should be handled immediately.
> > - */
> > - while (!virtqueue_get_buf(vi->cvq, &tmp) &&
> > - !virtqueue_is_broken(vi->cvq))
> > - cpu_relax();
> > + virtqueue_wait_for_used(vi->cvq, &tmp);
> >
> > return vi->ctrl->status == VIRTIO_NET_OK;
> > }
> > @@ -3524,7 +3525,7 @@ static int virtnet_find_vqs(struct virtnet_info *vi)
> >
> > /* Parameters for control virtqueue, if any */
> > if (vi->has_cvq) {
> > - callbacks[total_vqs - 1] = NULL;
> > + callbacks[total_vqs - 1] = virtnet_cvq_done;
>
> If we're using CVQ callback, what is the actual use of the timeout?
Because we can't sleep forever since locks could be held like RTNL_LOCK.
>
> I'd say there is no right choice neither in the right timeout value
> nor in the action to take.
In the next version, I tend to put BAD_RING() to prevent future requests.
> Why not simply trigger the cmd and do all
> the changes at command return?
I don't get this, sorry.
>
> I suspect the reason is that it complicates the code. For example,
> having the possibility of many in flight commands, races between their
> completion, etc.
Actually the cvq command was serialized through RTNL_LOCK, so we don't
need to worry about this.
In the next version I can add ASSERT_RTNL().
Thanks
> The virtio standard does not even cover unordered
> used commands if I'm not wrong.
>
> Is there any other fundamental reason?
>
> Thanks!
>
> > names[total_vqs - 1] = "control";
> > }
> >
> > --
> > 2.25.1
> >
>
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