On Thu, May 27, 2021 at 4:43 PM Jason Wang [off-list ref] wrote:

在 2021/5/27 下午4:41, Jason Wang 写道:

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在 2021/5/27 下午3:34, Yongji Xie 写道:

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

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在 2021/5/27 下午1:08, Yongji Xie 写道:

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

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在 2021/5/27 下午12:57, Yongji Xie 写道:

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

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在 2021/5/17 下午5:55, Xie Yongji 写道:

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+
+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.

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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.

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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(). Is it ok to just
notify userspace to stop data path asynchronously? Userspace should
not be able to do any I/O at that time because the iotlb mapping is
already removed.

Thanks,
Yongji