Re: [RFC PATCH v4 02/10] vfio/pci: macros to generate module_init and module_exit for vendor modules

Cornelia Huck
2020-06-04T15:01:21Z

On Sun, 17 May 2020 22:45:10 -0400
Yan Zhao <yan.y.zhao@intel.com> wrote:

> vendor modules call macro module_vfio_pci_register_vendor_handler to
> generate module_init and module_exit.
> It is necessary 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 add refs of vfio_pci on a successful calling of
> vfio_pci_register_vendor_driver() and deref of vfio_pci on a
> successful calling of vfio_pci_unregister_vendor_driver().
> - vfio_pci only adds refs of vendor module on a successful probe of vendor
> driver.
> vfio_pci derefs vendor module when unbinding from a device.
>
> So, 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() in its module_exit, vfio_pci may
> hold a stale pointer to vendor module.
>
> Cc: Kevin Tian <kevin.tian@intel.com>
> Suggested-by: Alex Williamson <alex.williamson@redhat.com>
> Signed-off-by: Yan Zhao <yan.y.zhao@intel.com>
> ---
> include/linux/vfio.h | 27 +++++++++++++++++++++++++++
> 1 file changed, 27 insertions(+)
>
> diff --git a/include/linux/vfio.h b/include/linux/vfio.h
> index 3e53deb012b6..f3746608c2d9 100644
> --- a/include/linux/vfio.h
> +++ b/include/linux/vfio.h
> @@ -223,4 +223,31 @@ struct vfio_pci_vendor_driver_ops {
> };
> int __vfio_pci_register_vendor_driver(struct vfio_pci_vendor_driver_ops *ops);
> void vfio_pci_unregister_vendor_driver(struct vfio_device_ops *device_ops);
> +
> +#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); \

What if this function fails (e.g. with -ENOMEM)?

> + 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 */