Re: [PATCH net] vsock/virtio: enable VQs early on probe

[Stefano Garzarella]

On Tue, Mar 22, 2022 at 10:09:06AM -0400, Michael S. Tsirkin wrote:
> On Tue, Mar 22, 2022 at 03:05:00PM +0100, Stefano Garzarella wrote:
> > On Tue, Mar 22, 2022 at 09:36:14AM -0400, Michael S. Tsirkin wrote:
> > > On Tue, Mar 22, 2022 at 11:38:23AM +0100, Stefano Garzarella wrote:
> > > > virtio spec requires drivers to set DRIVER_OK before using VQs.
> > > > This is set automatically after probe returns, but virtio-vsock
> > > > driver uses VQs in the probe function to fill rx and event VQs
> > > > with new buffers.
> > >
> > >
> > > So this is a spec violation. absolutely.
> > >
> > > > Let's fix this, calling virtio_device_ready() before using VQs
> > > > in the probe function.
> > > >
> > > > Fixes: 0ea9e1d3a9e3 ("VSOCK: Introduce virtio_transport.ko")
> > > > Signed-off-by: Stefano Garzarella <sgarzare@xxxxxxxxxx>
> > > > ---
> > > >  net/vmw_vsock/virtio_transport.c | 2 ++
> > > >  1 file changed, 2 insertions(+)
> > > >
> > > > diff --git a/net/vmw_vsock/virtio_transport.c b/net/vmw_vsock/virtio_transport.c
> > > > index 5afc194a58bb..b1962f8cd502 100644
> > > > --- a/net/vmw_vsock/virtio_transport.c
> > > > +++ b/net/vmw_vsock/virtio_transport.c
> > > > @@ -622,6 +622,8 @@ static int virtio_vsock_probe(struct virtio_device *vdev)
> > > >  	INIT_WORK(&vsock->event_work, virtio_transport_event_work);
> > > >  	INIT_WORK(&vsock->send_pkt_work, virtio_transport_send_pkt_work);
> > > >
> > > > +	virtio_device_ready(vdev);
> > > > +
> > > >  	mutex_lock(&vsock->tx_lock);
> > > >  	vsock->tx_run = true;
> > > >  	mutex_unlock(&vsock->tx_lock);
> > >
> > > Here's the whole code snippet:
> > >
> > >
> > >        mutex_lock(&vsock->tx_lock);
> > >        vsock->tx_run = true;
> > >        mutex_unlock(&vsock->tx_lock);
> > >
> > >        mutex_lock(&vsock->rx_lock);
> > >        virtio_vsock_rx_fill(vsock);
> > >        vsock->rx_run = true;
> > >        mutex_unlock(&vsock->rx_lock);
> > >
> > >        mutex_lock(&vsock->event_lock);
> > >        virtio_vsock_event_fill(vsock);
> > >        vsock->event_run = true;
> > >        mutex_unlock(&vsock->event_lock);
> > >
> > >        if (virtio_has_feature(vdev, VIRTIO_VSOCK_F_SEQPACKET))
> > >                vsock->seqpacket_allow = true;
> > >
> > >        vdev->priv = vsock;
> > >        rcu_assign_pointer(the_virtio_vsock, vsock);
> > >
> > >        mutex_unlock(&the_virtio_vsock_mutex);
> > >
> > >
> > > I worry that this is not the only problem here:
> > > seqpacket_allow and setting of vdev->priv at least after
> > > device is active look suspicious.
> >
> > Right, so if you agree I'll move these before virtio_device_ready().
> >
> > > E.g.:
> > >
> > > static void virtio_vsock_event_done(struct virtqueue *vq)
> > > {
> > >        struct virtio_vsock *vsock = vq->vdev->priv;
> > >
> > >        if (!vsock)
> > >                return;
> > >        queue_work(virtio_vsock_workqueue, &vsock->event_work);
> > > }
> > >
> > > looks like it will miss events now they will be reported earlier.
> > > One might say that since vq has been kicked it might send
> > > interrupts earlier too so not a new problem, but
> > > there's a chance device actually waits until DRIVER_OK
> > > to start operating.
> >
> > Yes I see, should I break into 2 patches (one where I move the code already
> > present and this one)?
> >
> > Maybe a single patch is fine since it's the complete solution.
> >
> > Thank you for the detailed explanation,
> > Stefano
>
> Two I think since movement can be backported to before the hardening
> effort.

Yep, maybe 3 since seqpacket was added later.

Thanks,
Stefano