linux-kernel - [RFC PATCH v2 4/9] vfio/pci: macros to generate module_init and module

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Date:   Thu, 30 Jan 2020 21:11:40 -0500
From:   Yan Zhao <yan.y.zhao@...el.com>
To:     alex.williamson@...hat.com
Cc:     kvm@...r.kernel.org, linux-kernel@...r.kernel.org,
        cohuck@...hat.com, zhenyuw@...ux.intel.com, zhi.a.wang@...el.com,
        kevin.tian@...el.com, shaopeng.he@...el.com, yi.l.liu@...el.com,
        Yan Zhao <yan.y.zhao@...el.com>
Subject: [RFC PATCH v2 4/9] vfio/pci: macros to generate module_init and module_exit for vendor modules

vendor modules call macro module_vfio_pci_register_vendor_handler to
generate module_init and module_exit.
It is a must to ensure that vendor modules always call
vfio_pci_register_vendor_driver() on driver loading and
vfio_pci_unregister_vendor_driver on driver unloading,
because
(1) at compiling time, there's only a dependency of vendor modules on
vfio_pci.
(2) at runtime,
- vendor modules trigger module ref inc of vfio_pci when
  vfio_pci_register_vendor_driver() succeeds and module ref dec of vfio_pci
  when vfio_pci_unregister_vendor_driver() succeeds.
- vfio_pci adds refs of vendor module on a successful probe of vendor
  driver.
  vfio_pci derefs vendor module when unbinding from a device.

After vfio_pci is unbound from a device, the vendor module to that
device is free to get unloaded. However, if that vendor module does not
call vfio_pci_unregister_vendor_driver() before its module_exit, vfio_pc
may hold a stale pointer to vendor module and would be able to get unloaded
for the ref increased in vfio_pci_register_vendor_driver();

That's how module_vfio_pci_register_vendor_handler helps.

Suggested-by: Alex Williamson <alex.williamson@...hat.com>

Cc: Kevin Tian <kevin.tian@...el.com>
Signed-off-by: Yan Zhao <yan.y.zhao@...el.com>
---
 include/linux/vfio.h | 27 +++++++++++++++++++++++++++
 1 file changed, 27 insertions(+)

diff --git a/include/linux/vfio.h b/include/linux/vfio.h
index 69519cf1fd4f..386d1b19da3d 100644
--- a/include/linux/vfio.h
+++ b/include/linux/vfio.h
@@ -226,4 +226,31 @@ extern int vfio_pci_mmap(void *device_data, struct vm_area_struct *vma);
 extern void vfio_pci_request(void *device_data, unsigned int count);
 extern int vfio_pci_open(void *device_data);
 extern void vfio_pci_release(void *device_data);
+
+#define vfio_pci_register_vendor_driver(__name, __probe, __remove,	\
+					__device_ops)			\
+static struct vfio_pci_vendor_driver_ops  __ops ## _node = {		\
+	.owner		= THIS_MODULE,					\
+	.name		= __name,					\
+	.probe		= __probe,					\
+	.remove		= __remove,					\
+	.device_ops	= __device_ops,					\
+};									\
+__vfio_pci_register_vendor_driver(&__ops ## _node)
+
+#define module_vfio_pci_register_vendor_handler(name, probe, remove,	\
+						device_ops)		\
+static int __init device_ops ## _module_init(void)			\
+{									\
+	vfio_pci_register_vendor_driver(name, probe, remove,		\
+					device_ops);			\
+	return 0;							\
+};									\
+static void __exit device_ops ## _module_exit(void)			\
+{									\
+	vfio_pci_unregister_vendor_driver(device_ops);			\
+};									\
+module_init(device_ops ## _module_init);				\
+module_exit(device_ops ## _module_exit)
+
 #endif /* VFIO_H */
-- 
2.17.1