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

Matthew Rosato
2023-02-03T21:50:41Z

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(-)

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2.39.1