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

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Message-ID: <e7929cb0-ccb1-46c9-99bf-2c6035eb7c01@uipath.com>
Date:   Mon, 23 Oct 2023 19:28:30 +0300
From:   Alexandru Matei <alexandru.matei@...ath.com>
To:     Stefano Garzarella <sgarzare@...hat.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>,
        Alexandru Matei <alexandru.matei@...ath.com>
Subject: Re: [PATCH v2] vsock/virtio: initialize the_virtio_vsock before using
 VQs

On 10/23/2023 7:10 PM, Stefano Garzarella wrote:
> On Mon, Oct 23, 2023 at 06:36:21PM +0300, Alexandru Matei wrote:
>> On 10/23/2023 6:13 PM, Stefano Garzarella wrote:
>>> 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.
>>>
>>
>> We need rcu_assign_pointer after setting tx_run to true for connections that are initiated from the guest -> host.
>> virtio_transport_connect() calls virtio_transport_send_pkt().  Once 'the_virtio_vsock' is initialized, virtio_transport_send_pkt() will queue the packet,
>> but virtio_transport_send_pkt_work() will exit if tx_run is false.
> 
> Okay, but in this case we could safely queue &vsock->send_pkt_work after finishing initialization to send those packets queued earlier.
> 
> In the meantime I'll try to see if we can leave the initialization of `the_virtio_vsock` as the ulitmate step and maybe go out first in the workers if it's not set.
> 
> That way just queue all the workers after everything is done and we should be fine.
> 

Yep, Thanks for input, I'll send another patch with this approach.
I'll keep virtio_vsock_vqs_init() split in virtio_vsock_vqs_init() and virtio_vsock_vqs_start(), 
move tx_run setting in virtio_vsock_vqs_start() and queue &vsock->send_pkt_work after virtio_vsock_vqs_start() is called. 

>>
>>>>>
>>>>
>>>> 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.
>>>
>>
>> OK, how does virtio_vsock_vqs_setup() sound?
> 
> Or virtio_vsock_start() (without vqs)
> 
> Stefano
> 
>>
>>> 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
>>>>>>>
>>>>>>
>>>>
>>>
>>
>