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

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Date:   Tue, 22 Mar 2022 10:09:06 -0400
From:   "Michael S. Tsirkin" <mst@...hat.com>
To:     Stefano Garzarella <sgarzare@...hat.com>
Cc:     netdev@...r.kernel.org, virtualization@...ts.linux-foundation.org,
        "David S. Miller" <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>,
        Stefan Hajnoczi <stefanha@...hat.com>, kvm@...r.kernel.org,
        linux-kernel@...r.kernel.org, Paolo Abeni <pabeni@...hat.com>
Subject: Re: [PATCH net] vsock/virtio: enable VQs early on probe

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@...hat.com>
> > > ---
> > >  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.

-- 
MST