[PATCH 0/7] vfio: Fix release ordering races and use driver_override

[Alex Williamson]

VM hotplug testing reveals a number of races in the vfio device,
group, container shutdown path, some attributed to libvirt's ask/take
unplug behavior and some long standing with groups potentially
composed of multiple devices, where each device can be independently
bound to drivers.  Libvirt's ask/take behavior is a result of the
asynchronous nature of PCI hotplug, libvirt registers a hot-unplug
request (ask), which is acknowledged almost immediately and then
proceeds to try to unbind the device from the vfio bus driver (take).
This sets us off on racing paths where we allow the device to be
released from the group much like would happen in groups with multiple
devices, while the group and container are torn down separately.
These races are addressed in the first 3 patches of this series.

The long standing issue with removing devices from in-use groups is
that we feel that the system is compromised if we allow user and host
devices within the same non-isolated group.  This triggers a BUG_ON
when we detect this condition after the rogue driver binding.  Since
that code was put in place we've added driver_override support for
all of the physical buses supported by vfio, giving us a way to block
binding to such compromising drivers.  We finally enable that in the
latter 4 patches of this series, minding that we need to allow
re-binding to non-compromising drivers, and also noting that a small
synchronization stall is effective in eliminating the need for this
blocking in the more common singleton device group case.

Reviews, comments, and acks appreciated.  Thanks,

Alex
---

Alex Williamson (7):
      vfio: Fix group release deadlock
      kvm-vfio: Decouple only when we match a group
      vfio: New external user group/file match
      iommu: Add driver-not-bound notification
      vfio: Create interface for vfio bus drivers to register
      vfio: Register pci, platform, amba, and mdev bus drivers
      vfio: Use driver_override to avert binding to compromising drivers


 drivers/iommu/iommu.c                 |    2 
 drivers/vfio/mdev/vfio_mdev.c         |   13 ++
 drivers/vfio/pci/vfio_pci.c           |    7 +
 drivers/vfio/platform/vfio_amba.c     |   24 +++
 drivers/vfio/platform/vfio_platform.c |   24 +++
 drivers/vfio/vfio.c                   |  252 ++++++++++++++++++++++++++++++++-
 include/linux/iommu.h                 |    1 
 include/linux/vfio.h                  |    5 +
 virt/kvm/vfio.c                       |   33 +++-
 9 files changed, 338 insertions(+), 23 deletions(-)