Re: [PATCH] uacce: unmap remaining mmapping from user space

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Hi,
On 2020/2/25 16:33, zhangfei wrote:
Hi, Zaibo

On 2020/2/24 下午3:17, Xu Zaibo wrote:
  @@ -585,6 +595,13 @@ void uacce_remove(struct uacce_device *uacce)
          cdev_device_del(uacce->cdev, &uacce->dev);
      xa_erase(&uacce_xa, uacce->dev_id);
      put_device(&uacce->dev);
+
+    /*
+     * unmap remainning mapping from user space, preventing user still
+     * access the mmaped area while parent device is already removed
+     */
+    if (uacce->inode)
+        unmap_mapping_range(uacce->inode->i_mapping, 0, 0, 1);
Should we unmap them at the first of 'uacce_remove', and before 'uacce_put_queue'?

We can do this,
Though it does not matter, since user space can not interrupt kernel function uacce_remove.

I think it matters :)

Image that the process holds the uacce queue is running(read and write the queue), then you do 'uacce_remove'. The process is running(read and write the queue) well in the time between 'uacce_put_queue' and 'unmap_mapping_range', however, the queue with its DMA memory may be gotten and used by other guys in this time, since you have released them in kernel. As a result, the running process will be a disaster.

cheers,
Zaibo

.


Thanks
.






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