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

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Date:   Fri,  3 Feb 2023 16:50:25 -0500
From:   Matthew Rosato <mjrosato@...ux.ibm.com>
To:     alex.williamson@...hat.com, pbonzini@...hat.com,
        yi.l.liu@...el.com, jgg@...dia.com
Cc:     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: [PATCH v4 0/2] vfio: fix deadlock between group lock and kvm lock

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(-)

-- 
2.39.1