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

On Thu, May 27, 2021 at 1:40 PM Jason Wang [off-list ref] wrote:

在 2021/5/27 下午1:08, Yongji Xie 写道:

quoted

On Thu, May 27, 2021 at 1:00 PM Jason Wang [off-list ref] wrote:

quoted

在 2021/5/27 下午12:57, Yongji Xie 写道:

quoted

On Thu, May 27, 2021 at 12:13 PM Jason Wang [off-list ref] wrote:

quoted

在 2021/5/17 下午5:55, Xie Yongji 写道:

quoted

+
+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.

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

Could it handle the failure of get_feature() and get/set_config()?

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.

Thanks,
Yongji