netdev - Re: [PATCH v2] vsock/virtio: initialize the_virtio

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Date: Mon, 23 Oct 2023 17:13:07 +0200
From: Stefano Garzarella <sgarzare@...hat.com>
To: Alexandru Matei <alexandru.matei@...ath.com>
Cc: Stefan Hajnoczi <stefanha@...hat.com>, 
	"David S . Miller" <davem@...emloft.net>, Eric Dumazet <edumazet@...gle.com>, 
	Jakub Kicinski <kuba@...nel.org>, Paolo Abeni <pabeni@...hat.com>, kvm@...r.kernel.org, 
	virtualization@...ts.linux-foundation.org, netdev@...r.kernel.org, linux-kernel@...r.kernel.org, 
	Mihai Petrisor <mihai.petrisor@...ath.com>, Viorel Canja <viorel.canja@...ath.com>
Subject: Re: [PATCH v2] vsock/virtio: initialize the_virtio_vsock before
 using VQs

On Mon, Oct 23, 2023 at 05:59:45PM +0300, Alexandru Matei wrote:
>On 10/23/2023 5:52 PM, Alexandru Matei wrote:
>> On 10/23/2023 5:29 PM, Stefano Garzarella wrote:
>>> On Mon, Oct 23, 2023 at 05:08:33PM +0300, Alexandru Matei wrote:
>>>> Once VQs are filled with empty buffers and we kick the host,
>>>> it can send connection requests.  If 'the_virtio_vsock' is not
>>>> initialized before, replies are silently dropped and do not reach the host.
>>>>
>>>> Fixes: 0deab087b16a ("vsock/virtio: use RCU to avoid use-after-free on the_virtio_vsock")
>>>> Signed-off-by: Alexandru Matei <alexandru.matei@...ath.com>
>>>> ---
>>>> v2:
>>>> - split virtio_vsock_vqs_init in vqs_init and vqs_fill and moved
>>>>  the_virtio_vsock initialization after vqs_init
>>>>
>>>> net/vmw_vsock/virtio_transport.c | 9 +++++++--
>>>> 1 file changed, 7 insertions(+), 2 deletions(-)
>>>>
>>>> diff --git a/net/vmw_vsock/virtio_transport.c b/net/vmw_vsock/virtio_transport.c
>>>> index e95df847176b..92738d1697c1 100644
>>>> --- a/net/vmw_vsock/virtio_transport.c
>>>> +++ b/net/vmw_vsock/virtio_transport.c
>>>> @@ -559,6 +559,11 @@ static int virtio_vsock_vqs_init(struct virtio_vsock *vsock)
>>>>     vsock->tx_run = true;
>>>>     mutex_unlock(&vsock->tx_lock);
>>>>
>>>> +    return 0;
>>>> +}
>>>> +
>>>> +static void virtio_vsock_vqs_fill(struct virtio_vsock *vsock)
>>>
>>> What about renaming this function in virtio_vsock_vqs_start() and move also the setting of `tx_run` here?
>>
>> It works but in this case we also need to move rcu_assign_pointer in virtio_vsock_vqs_start(),
>> the assignment needs to be right after setting tx_run to true and before filling the VQs.

Why?

If `rx_run` is false, we shouldn't need to send replies to the host 
IIUC.

If we need this instead, please add a comment in the code, but also in 
the commit, because it's not clear why.

>>
>
>And if we move rcu_assign_pointer then there is no need to split the function in two,
>We can move rcu_assign_pointer() directly inside virtio_vsock_vqs_init() after setting tx_run.

Yep, this could be another option, but we need to change the name of 
that function in this case.

Stefano

>
>>>
>>> Thanks,
>>> Stefano
>>>
>>>> +{
>>>>     mutex_lock(&vsock->rx_lock);
>>>>     virtio_vsock_rx_fill(vsock);
>>>>     vsock->rx_run = true;
>>>> @@ -568,8 +573,6 @@ static int virtio_vsock_vqs_init(struct virtio_vsock *vsock)
>>>>     virtio_vsock_event_fill(vsock);
>>>>     vsock->event_run = true;
>>>>     mutex_unlock(&vsock->event_lock);
>>>> -
>>>> -    return 0;
>>>> }
>>>>
>>>> static void virtio_vsock_vqs_del(struct virtio_vsock *vsock)
>>>> @@ -664,6 +667,7 @@ static int virtio_vsock_probe(struct virtio_device *vdev)
>>>>         goto out;
>>>>
>>>>     rcu_assign_pointer(the_virtio_vsock, vsock);
>>>> +    virtio_vsock_vqs_fill(vsock);
>>>>
>>>>     mutex_unlock(&the_virtio_vsock_mutex);
>>>>
>>>> @@ -736,6 +740,7 @@ static int virtio_vsock_restore(struct virtio_device *vdev)
>>>>         goto out;
>>>>
>>>>     rcu_assign_pointer(the_virtio_vsock, vsock);
>>>> +    virtio_vsock_vqs_fill(vsock);
>>>>
>>>> out:
>>>>     mutex_unlock(&the_virtio_vsock_mutex);
>>>> -- 
>>>> 2.34.1
>>>>
>>>
>