Jason Wang
2021-May-28 01:33 UTC
[PATCH v7 11/12] vduse: Introduce VDUSE - vDPA Device in Userspace
? 2021/5/27 ??6:14, Yongji Xie ??:> On Thu, May 27, 2021 at 4:43 PM Jason Wang <jasowang at redhat.com> wrote: >> >> ? 2021/5/27 ??4:41, Jason Wang ??: >>> ? 2021/5/27 ??3:34, Yongji Xie ??: >>>> On Thu, May 27, 2021 at 1:40 PM Jason Wang <jasowang at redhat.com> wrote: >>>>> ? 2021/5/27 ??1:08, Yongji Xie ??: >>>>>> On Thu, May 27, 2021 at 1:00 PM Jason Wang <jasowang at redhat.com> >>>>>> wrote: >>>>>>> ? 2021/5/27 ??12:57, Yongji Xie ??: >>>>>>>> On Thu, May 27, 2021 at 12:13 PM Jason Wang <jasowang at redhat.com> >>>>>>>> wrote: >>>>>>>>> ? 2021/5/17 ??5:55, Xie Yongji ??: >>>>>>>>>> + >>>>>>>>>> +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 >>> 3) extend the spec to use vq instead of config space >>> >>> Thanks >> >> Another thing if we want to go this way: >> >> We need find a way to terminate the data path from the kernel side, to >> implement to reset semantic. >> > Do you mean terminate the data path in vdpa_reset().Yes.> Is it ok to just > notify userspace to stop data path asynchronously?For well-behaved userspace, yes but no for buggy or malicious ones. I had an idea, how about terminate IOTLB in this case? Then we're in fact turn datapath off. Thanks> Userspace should > not be able to do any I/O at that time because the iotlb mapping is > already removed. > > Thanks, > Yongji >