linux-kernel - Re: [PATCH v4 0/2] vfio: fix deadlock between group lock and kvm lock

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Date:   Thu, 9 Feb 2023 14:03:26 -0700
From:   Alex Williamson <alex.williamson@...hat.com>
To:     Matthew Rosato <mjrosato@...ux.ibm.com>
Cc:     pbonzini@...hat.com, yi.l.liu@...el.com, jgg@...dia.com,
        cohuck@...hat.com, farman@...ux.ibm.com, pmorel@...ux.ibm.com,
        borntraeger@...ux.ibm.com, frankja@...ux.ibm.com,
        imbrenda@...ux.ibm.com, david@...hat.com, akrowiak@...ux.ibm.com,
        jjherne@...ux.ibm.com, pasic@...ux.ibm.com,
        zhenyuw@...ux.intel.com, zhi.a.wang@...el.com, seanjc@...gle.com,
        kevin.tian@...el.com, linux-s390@...r.kernel.org,
        kvm@...r.kernel.org, intel-gvt-dev@...ts.freedesktop.org,
        intel-gfx@...ts.freedesktop.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v4 0/2] vfio: fix deadlock between group lock and kvm
 lock

On Fri,  3 Feb 2023 16:50:25 -0500
Matthew Rosato <mjrosato@...ux.ibm.com> wrote:

> Hi Alex,
> 
> Here is the latest group_lock vs kvm lock deadlock fix + a non-fix
> follow-on to remove the kvm argument from vfio_device_open and
> vfio_device_first_open.
> 
> Changes from v3:
> * Remove device->group->kvm reference in vfio_main by passing the
>   kvm in (Kevin)
> * Slight re-organization to make it easier for cdev to build upon
>   this later and keep symmetry between get/put (Alex)
> * Add follow-on patch that removes unused kvm argument (Yi)
> 
> Changes from v2:
> * Relocate the new functions back to vfio_main and externalize to call
>   from group (Kevin) since cdev will need this too
> * s/vfio_kvm_*_kvm/vfio_device_*_kvm/ and only pass device as input.
>   Handle new kvm_ref_lock directly inside vfio_device_get_kvm (Alex)
> * Add assert_lockdep_held for dev_set lock (Alex)
> * Internalize error paths for vfio_device_get_kvm_safe and now return
>   void - either device->kvm is set with a ref taken or is NULL (Alex)
> * Other flow suggestions to make the call path cleaner - Thanks! (Alex)
> * Can't pass group->kvm to vfio_device_open, as it references the value
>   outside of new lock.  Pass device->kvm to minimize changes in this
>   fix (Alex, Yi)
> 
> Changes from v1:
> * use spin_lock instead of spin_lock_irqsave (Jason)
> * clear device->kvm_put as part of vfio_kvm_put_kvm (Yi)
> * Re-arrange code to avoid referencing the group contents from within
>   vfio_main (Kevin) which meant moving most of the code in this patch 
>   to group.c along with getting/dropping of the dev_set lock
> 
> Matthew Rosato (2):
>   vfio: fix deadlock between group lock and kvm lock
>   vfio: no need to pass kvm pointer during device open
> 
>  drivers/vfio/group.c     | 44 +++++++++++++++++++++----
>  drivers/vfio/vfio.h      | 18 +++++++++--
>  drivers/vfio/vfio_main.c | 70 +++++++++++++++++++++++++++++++++-------
>  include/linux/vfio.h     |  2 +-
>  4 files changed, 113 insertions(+), 21 deletions(-)
> 

Applied to vfio next branch for v6.3.  Thanks,

Alex