Virtualization - Mar 2022 - [PATCH net] vsock/virtio: enable VQs early on probe

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 at redhat.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.
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.

> -- 
> 2.35.1

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 at redhat.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