[PATCH v3 0/1] vfio: remove VFIO_GROUP_NOTIFY_SET_KVM

Matthew Rosato
2022-05-19T18:33:33Z

As discussed in this thread:

https://lore.kernel.org/kvm/20220516172734.GE1343366@nvidia.com/

Let's remove VFIO_GROUP_NOTIFY_SET_KVM and instead assume the association
has already been established prior to device_open. For the types today
that need a KVM (GVT, vfio-ap) these will fail if a KVM is not found.
Looking ahead, vfio-pci-zdev will optionally want the KVM association
(enable hardware assists) but it will not be a hard requirement (still
want to allow other, non-KVM userspace usage).

This is built on top of vfio-next and tested with s390x-pci
(zdev-kvm series) and vfio-ap (GVT changes are compile-tested only)

Changes for v3:
- merge branches under if (device->open_count == 1) (Kevin)
- move device->open_count-- out from group_rwsem (Kevin)
- drop null KVM check (Christoph)
- remove extra kvm_{get,put}_kvm from vfio_ap_ops, it was already getting
a reference (Jason)
- Add comment about kvm reference in vfio.h (Jason)
- Return -EINVAL if !kvm for vfio-ap (Tony)

Changes for v2:
- gvt no longer needs release_work, get rid of it (Christoph)
- a few compile fixes for gvt
- update commit to mention fixes gvt oops (Jason)
- s/down_write/down_read/ in a few spots (Jason)
- avoid kvm build dependency by holding group read lock over device
open/close and put the onus on the driver to obtain a reference if
it will actually use the kvm pointer. Document the requirement,
use lockdep_assert to ensure lock is held during register_notifer;
today all callers are from driver open_device.

Matthew Rosato (1):
vfio: remove VFIO_GROUP_NOTIFY_SET_KVM

drivers/gpu/drm/i915/gvt/gtt.c | 4 +-
drivers/gpu/drm/i915/gvt/gvt.h | 3 -
drivers/gpu/drm/i915/gvt/kvmgt.c | 82 ++++++--------------------
drivers/s390/crypto/vfio_ap_ops.c | 35 ++---------
drivers/s390/crypto/vfio_ap_private.h | 3 -
drivers/vfio/vfio.c | 83 ++++++++++-----------------
include/linux/vfio.h | 6 +-
7 files changed, 57 insertions(+), 159 deletions(-)

--
2.27.0