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

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Message-ID: <f20edd55-20cb-c016-b347-dd71c5406ed8@redhat.com>
Date:   Fri, 28 May 2021 10:31:02 +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9:17, Yongji Xie 写道:
> On Thu, May 27, 2021 at 4:41 PM Jason Wang <jasowang@...hat.com> wrote:
>>
>> 在 2021/5/27 下午3:34, Yongji Xie 写道:
>>> On Thu, May 27, 2021 at 1:40 PM Jason Wang <jasowang@...hat.com> wrote:
>>>> 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 need to change all virtio device drivers in this way.
>>
>> Probably.
>>
>>
>>>> We had NEEDS_RESET but it looks we don't implement it.
>>>>
>>> Could it handle the failure of get_feature() and get/set_config()?
>>
>> Looks not:
>>
>> "
>>
>> The device SHOULD set DEVICE_NEEDS_RESET when it enters an error state
>> that a reset is needed. If DRIVER_OK is set, after it sets
>> DEVICE_NEEDS_RESET, the device MUST send a device configuration change
>> notification to the driver.
>>
>> "
>>
>> This looks implies that NEEDS_RESET may only work after device is
>> probed. But in the current design, even the reset() is not reliable.
>>
>>
>>>> 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.
>>>>
>>> I think it can work for most cases. One problem is that the set_config
>>> might change the behavior of the data path at runtime, e.g.
>>> virtnet_set_mac_address() in the virtio-net driver and
>>> cache_type_store() in the virtio-blk driver. Not sure if this path is
>>> able to return before the datapath is aware of this change.
>>
>> Good point.
>>
>> But set_config() should be rare:
>>
>> E.g in the case of virtio-net with VERSION_1, config space is read only,
>> and it was set via control vq.
>>
>> For block, we can
>>
>> 1) start from without WCE or
>> 2) we add a config change notification to userspace or
> I prefer this way. And I think we also need to do similar things for
> set/get_vq_state().


Yes, I agree.

Thanks


>
> Thanks,
> Yongji
>