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

[Jason Wang]

在 2022/12/27 14:58, Michael S. Tsirkin 写道:
> On Tue, Dec 27, 2022 at 12:33:53PM +0800, Jason Wang wrote:
> > 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.
> Controlling timeout from device is a good idea, e.g. hardware devices
> would benefit from a shorter timeout, hypervisor devices from a longer
> timeout or no timeout.


Yes.


> > > 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.
> Spec says nothing about this, so driver can't assume this either.


Well, my understanding is that it's more than what spec can define or 
it's a kind of best practice.

The current code is one example, that is, driver may choose to busy poll 
which cause spike.


> > > In particular, we will also directly break the device.
> > It's kind of hardening for malicious devices.
> ATM no amount of hardening can prevent a malicious hypervisor from
> blocking the guest. Recovering when a hardware device is broken would be
> nice but I think if we do bother then we should try harder to recover,
> such as by driving device reset.


Probably, but as discussed in another thread, it needs co-operation in 
the upper layer (networking core).


> Also, does your patch break surprise removal? There's no callback
> in this case ATM.


I think not (see reply in another thread).

Thanks


> > > 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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