linux-kernel - Re: [PATCH v4 00/15] Tidy up vfio

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Message-ID: <20220922115820.5ac023ab.alex.williamson@redhat.com>
Date:   Thu, 22 Sep 2022 11:58:20 -0600
From:   Alex Williamson <alex.williamson@...hat.com>
To:     Kevin Tian <kevin.tian@...el.com>
Cc:     Zhenyu Wang <zhenyuw@...ux.intel.com>,
        Zhi Wang <zhi.a.wang@...el.com>,
        Jani Nikula <jani.nikula@...ux.intel.com>,
        Joonas Lahtinen <joonas.lahtinen@...ux.intel.com>,
        Rodrigo Vivi <rodrigo.vivi@...el.com>,
        Tvrtko Ursulin <tvrtko.ursulin@...ux.intel.com>,
        David Airlie <airlied@...ux.ie>,
        Daniel Vetter <daniel@...ll.ch>,
        Eric Farman <farman@...ux.ibm.com>,
        Matthew Rosato <mjrosato@...ux.ibm.com>,
        Halil Pasic <pasic@...ux.ibm.com>,
        Vineeth Vijayan <vneethv@...ux.ibm.com>,
        Peter Oberparleiter <oberpar@...ux.ibm.com>,
        Heiko Carstens <hca@...ux.ibm.com>,
        Vasily Gorbik <gor@...ux.ibm.com>,
        Alexander Gordeev <agordeev@...ux.ibm.com>,
        Christian Borntraeger <borntraeger@...ux.ibm.com>,
        Sven Schnelle <svens@...ux.ibm.com>,
        Tony Krowiak <akrowiak@...ux.ibm.com>,
        Jason Herne <jjherne@...ux.ibm.com>,
        Harald Freudenberger <freude@...ux.ibm.com>,
        Diana Craciun <diana.craciun@....nxp.com>,
        Cornelia Huck <cohuck@...hat.com>,
        Longfang Liu <liulongfang@...wei.com>,
        Shameer Kolothum <shameerali.kolothum.thodi@...wei.com>,
        Jason Gunthorpe <jgg@...pe.ca>,
        Yishai Hadas <yishaih@...dia.com>,
        Eric Auger <eric.auger@...hat.com>,
        Kirti Wankhede <kwankhede@...dia.com>,
        Leon Romanovsky <leon@...nel.org>,
        Abhishek Sahu <abhsahu@...dia.com>,
        Christoph Hellwig <hch@...radead.org>,
        intel-gvt-dev@...ts.freedesktop.org,
        intel-gfx@...ts.freedesktop.org, dri-devel@...ts.freedesktop.org,
        linux-kernel@...r.kernel.org, linux-s390@...r.kernel.org,
        kvm@...r.kernel.org, Yi Liu <yi.l.liu@...el.com>
Subject: Re: [PATCH v4 00/15] Tidy up vfio_device life cycle

On Wed, 21 Sep 2022 18:43:46 +0800
Kevin Tian <kevin.tian@...el.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