vfio/mdev: Fix aborting mdev child device removal if one fails

mainline inclusion
from mainline-5.2-rc1
commit 6093e348
category: bugfix
bugzilla: 15887
CVE: NA

-------------------------------------------------

device_for_each_child() stops executing callback function for remaining
child devices, if callback hits an error.
Each child mdev device is independent of each other.
While unregistering parent device, mdev core must remove all child mdev
devices.
Therefore, mdev_device_remove_cb() always returns success so that
device_for_each_child doesn't abort if one child removal hits error.

While at it, improve remove and unregister functions for below simplicity.

There isn't need to pass forced flag pointer during mdev parent
removal which invokes mdev_device_remove(). So simplify the flow.

mdev_device_remove() is called from two paths.
1. mdev_unregister_driver()
     mdev_device_remove_cb()
       mdev_device_remove()
2. remove_store()
     mdev_device_remove()

Fixes: 7b96953b ("vfio: Mediated device Core driver")
Reviewed-by: NMaxim Levitsky <mlevitsk@redhat.com>
Signed-off-by: NParav Pandit <parav@mellanox.com>
Signed-off-by: NAlex Williamson <alex.williamson@redhat.com>
Signed-off-by: NYang Yingliang <yangyingliang@huawei.com>
Reviewed-by: NXuefeng Wang <wxf.wang@hisilicon.com>
Signed-off-by: NYang Yingliang <yangyingliang@huawei.com>

drivers/vfio/mdev/mdev_core.c

@@ -150,10 +150,10 @@ static int mdev_device_remove_ops(struct mdev_device *mdev, bool force_remove)
 
 static int mdev_device_remove_cb(struct device *dev, void *data)
 {
-	if (!dev_is_mdev(dev))
-		return 0;
+	if (dev_is_mdev(dev))
+		mdev_device_remove(dev, true);
 
-	return mdev_device_remove(dev, data ? *(bool *)data : true);
+	return 0;
 }
 
 /*
@@ -240,7 +240,6 @@ EXPORT_SYMBOL(mdev_register_device);
 void mdev_unregister_device(struct device *dev)
 {
 	struct mdev_parent *parent;
-	bool force_remove = true;
 
 	mutex_lock(&parent_list_lock);
 	parent = __find_parent_device(dev);
@@ -254,8 +253,7 @@ void mdev_unregister_device(struct device *dev)
 	list_del(&parent->next);
 	class_compat_remove_link(mdev_bus_compat_class, dev, NULL);
 
-	device_for_each_child(dev, (void *)&force_remove,
-			      mdev_device_remove_cb);
+	device_for_each_child(dev, NULL, mdev_device_remove_cb);
 
 	parent_remove_sysfs_files(parent);