Re: [PATCH v4 00/15] Tidy up vfio_device life cycle

[Alex Williamson <alex.williamson@redhat.com>]

On Wed, 21 Sep 2022 18:43:46 +0800
Kevin Tian <kevin.tian@intel.com> wrote:

> The idea is to let vfio core manage the vfio_device life cycle instead
> of duplicating the logic cross drivers. Besides cleaner code in driver
> side this also allows adding struct device to vfio_device as the first
> step toward adding cdev uAPI in the future. Another benefit is that
> user can now look at sysfs to decide whether a device is bound to
> vfio [1], e.g.:
> 
> 	/sys/devices/pci0000\:6f/0000\:6f\:01.0/vfio-dev/vfio0
> 
> Though most drivers can fit the new model naturally:
> 
>  - vfio_alloc_device() to allocate and initialize vfio_device
>  - vfio_put_device() to release vfio_device
>  - dev_ops->init() for driver private initialization
>  - dev_ops->release() for driver private cleanup
> 
> vfio-ccw is the only exception due to a life cycle mess that its private
> structure mixes both parent and mdev info hence must be alloc/freed
> outside of the life cycle of vfio device.
> 
> Per prior discussions this won't be fixed in short term by IBM folks [2].
> 
> Instead of waiting this series introduces a few tricks to move forward:
> 
>  - vfio_init_device() to initialize a pre-allocated device structure;
> 
>  - require *EVERY* driver to implement @release and free vfio_device
>    inside. Then vfio-ccw can use a completion mechanism to delay the
>    free to css driver;
> 
> The second trick is not a real burden to other drivers because they
> all require a @release for private cleanup anyway. Later once the ccw
> mess is fixed a simple cleanup can be done by moving free from @release
> to vfio core.
> 
> Thanks
> Kevin
> 
> [1] https://listman.redhat.com/archives/libvir-list/2022-August/233482.html
> [2] https://lore.kernel.org/all/0ee29bd6583f17f0ee4ec0769fa50e8ea6703623.camel@linux.ibm.com/
> 
> v4:
>  - fix use-after-free issue in @release of mtty/mbochs and also change
>    mdpy/ap to free vfio-device as the last thing in @release (Alex)
>  - revert the rename from 'vfio' to 'vfio_group' in procfs (Alex) 

Applied to vfio next branch for v6.1.  Thanks,

Alex