Re: Re: [PATCH v7 11/12] vduse: Introduce VDUSE - vDPA Device in Userspace

[Yongji Xie]

On Thu, May 27, 2021 at 4:41 PM Jason Wang <jasowang@xxxxxxxxxx> 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@xxxxxxxxxx> 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@xxxxxxxxxx> 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@xxxxxxxxxx> 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().

Thanks,
Yongji