Re: [PATCH 4/4] virtio-net: sleep instead of busy waiting for cvq command

[Jason Wang]

On Tue, Dec 27, 2022 at 10:25 AM Xuan Zhuo <xuanzhuo@xxxxxxxxxxxxxxxxx> wrote:
>
> On Mon, 26 Dec 2022 15:49:08 +0800, 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 virtqueue_wait_for_used() to sleep with a
> > timeout (1s) instead of busy polling for the cvq command forever. This
>
> I don't think that a fixed 1S is a good choice.

Well, it could be tweaked to be a little bit longer.

One way, as discussed, is to let the device advertise a timeout then
the driver can validate if it's valid and use that timeout. But it
needs extension to the spec.

> Some of the DPUs are very
> lazy for cvq handle.

Such design needs to be revisited, cvq (control path) should have a
better priority or QOS than datapath.

> In particular, we will also directly break the device.

It's kind of hardening for malicious devices.

>
> I think it is necessary to add a Virtio-Net parameter to allow users to define
> this timeout by themselves. Although I don't think this is a good way.

Very hard and unfriendly to the end users.

Thanks

>
> Thanks.
>
>
> > gives the scheduler a breath and can let the process can respond to
> > asignal. If the device doesn't respond in the timeout, break the
> > device.
> >
> > Signed-off-by: Jason Wang <jasowang@xxxxxxxxxx>
> > ---
> > Changes since V1:
> > - break the device when timeout
> > - get buffer manually since the virtio core check more_used() instead
> > ---
> >  drivers/net/virtio_net.c | 24 ++++++++++++++++--------
> >  1 file changed, 16 insertions(+), 8 deletions(-)
> >
> > diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c
> > index efd9dd55828b..6a2ea64cfcb5 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;
> > @@ -1984,6 +1990,8 @@ static int virtnet_tx_resize(struct virtnet_info *vi,
> >       return err;
> >  }
> >
> > +static int virtnet_close(struct net_device *dev);
> > +
> >  /*
> >   * Send command via the control virtqueue and check status.  Commands
> >   * supported by the hypervisor, as indicated by feature bits, should
> > @@ -2026,14 +2034,14 @@ 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();
> > +     if (virtqueue_wait_for_used(vi->cvq)) {
> > +             virtqueue_get_buf(vi->cvq, &tmp);
> > +             return vi->ctrl->status == VIRTIO_NET_OK;
> > +     }
> >
> > -     return vi->ctrl->status == VIRTIO_NET_OK;
> > +     netdev_err(vi->dev, "CVQ command timeout, break the virtio device.");
> > +     virtio_break_device(vi->vdev);
> > +     return VIRTIO_NET_ERR;
> >  }
> >
> >  static int virtnet_set_mac_address(struct net_device *dev, void *p)
> > @@ -3526,7 +3534,7 @@ 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;
> >               names[total_vqs - 1] = "control";
> >       }
> >
> > --
> > 2.25.1
> >
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