netdev - Re: [PATCH v7 11/12] vduse: Introduce VDUSE

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Date:   Thu, 27 May 2021 13:40:31 +0800
From:   Jason Wang <jasowang@...hat.com>
To:     Yongji Xie <xieyongji@...edance.com>
Cc:     "Michael S. Tsirkin" <mst@...hat.com>,
        Stefan Hajnoczi <stefanha@...hat.com>,
        Stefano Garzarella <sgarzare@...hat.com>,
        Parav Pandit <parav@...dia.com>,
        Christoph Hellwig <hch@...radead.org>,
        Christian Brauner <christian.brauner@...onical.com>,
        Randy Dunlap <rdunlap@...radead.org>,
        Matthew Wilcox <willy@...radead.org>,
        Al Viro <viro@...iv.linux.org.uk>,
        Jens Axboe <axboe@...nel.dk>, bcrl@...ck.org,
        Jonathan Corbet <corbet@....net>,
        Mika Penttilä <mika.penttila@...tfour.com>,
        Dan Carpenter <dan.carpenter@...cle.com>, joro@...tes.org,
        virtualization <virtualization@...ts.linux-foundation.org>,
        netdev@...r.kernel.org, kvm <kvm@...r.kernel.org>,
        linux-fsdevel@...r.kernel.org, iommu@...ts.linux-foundation.org,
        linux-kernel <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v7 11/12] vduse: Introduce VDUSE - vDPA Device in
 Userspace


在 2021/5/27 下午1:08, Yongji Xie 写道:
> On Thu, May 27, 2021 at 1:00 PM Jason Wang <jasowang@...hat.com> wrote:
>>
>> 在 2021/5/27 下午12:57, Yongji Xie 写道:
>>> On Thu, May 27, 2021 at 12:13 PM Jason Wang <jasowang@...hat.com> wrote:
>>>> 在 2021/5/17 下午5:55, Xie Yongji 写道:
>>>>> +
>>>>> +static int vduse_dev_msg_sync(struct vduse_dev *dev,
>>>>> +                           struct vduse_dev_msg *msg)
>>>>> +{
>>>>> +     init_waitqueue_head(&msg->waitq);
>>>>> +     spin_lock(&dev->msg_lock);
>>>>> +     vduse_enqueue_msg(&dev->send_list, msg);
>>>>> +     wake_up(&dev->waitq);
>>>>> +     spin_unlock(&dev->msg_lock);
>>>>> +     wait_event_killable(msg->waitq, msg->completed);
>>>> What happens if the userspace(malicous) doesn't give a response forever?
>>>>
>>>> It looks like a DOS. If yes, we need to consider a way to fix that.
>>>>
>>> How about using wait_event_killable_timeout() instead?
>>
>> Probably, and then we need choose a suitable timeout and more important,
>> need to report the failure to virtio.
>>
> Makes sense to me. But it looks like some
> vdpa_config_ops/virtio_config_ops such as set_status() didn't have a
> return value.  Now I add a WARN_ON() for the failure. Do you mean we
> need to add some change for virtio core to handle the failure?


Maybe, but I'm not sure how hard we can do that.

We had NEEDS_RESET but it looks we don't implement it.

Or a rough idea is that maybe need some relaxing to be coupled loosely 
with userspace. E.g the device (control path) is implemented in the 
kernel but the datapath is implemented in the userspace like TUN/TAP.

Thanks

>
> Thanks,
> Yongji
>