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

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Message-ID: <20220322143631.gt32cshbwyetq2fh@sgarzare-redhat>
Date:   Tue, 22 Mar 2022 15:36:31 +0100
From:   Stefano Garzarella <sgarzare@...hat.com>
To:     "Michael S. Tsirkin" <mst@...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 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@...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.

Yep, maybe 3 since seqpacket was added later.

Thanks,
Stefano