Merge branch 'v6.6/vfio/cdev' of https://github.com/awilliam/linux-vfio into iommufd...

Shared branch with VFIO containing the enablement for VFIO "cdev"
devices. This is required by following iommufd patches which add new
ioctls to the VFIO cdev.

=======
Existing VFIO provides group-centric user APIs for userspace. Userspace
opens the /dev/vfio/$group_id first before getting device fd and hence
getting access to device. This is not the desired model for iommufd. Per
the conclusion of community discussion[1], iommufd provides device-centric
kAPIs and requires its consumer (like VFIO) to be device-centric user
APIs. Such user APIs are used to associate device with iommufd and also
the I/O address spaces managed by the iommufd.

This series first introduces a per device file structure to be prepared
for further enhancement and refactors the kvm-vfio code to be prepared
for accepting device file from userspace. After this, adds a mechanism for
blocking device access before iommufd bind. Then refactors the vfio to be
able to handle cdev paths (e.g. iommufd binding, no-iommufd, [de]attach ioas).
This refactor includes making the device_open exclusive between the group
and the cdev path, only allow single device open in cdev path; vfio-iommufd
code is also refactored to support cdev. e.g. split the vfio_iommufd_bind()
into two steps. Eventually, adds the cdev support for vfio device and the
new ioctls, then makes group infrastructure optional as it is not needed
when vfio device cdev is compiled.

This series is based on some preparation works done to vfio emulated devices[2]
and vfio pci hot reset enhancements[3]. Per discussion[4], this series does not
support cdev for physical devices that do not have IOMMU. Such devices only
have group-centric user APIs.

This series is a prerequisite for iommu nesting for vfio device[5] [6].

[1] https://lore.kernel.org/kvm/BN9PR11MB5433B1E4AE5B0480369F97178C189@BN9PR11MB5433.namprd11.prod.outlook.com/
[2] https://lore.kernel.org/kvm/20230327093351.44505-1-yi.l.liu@intel.com/ - merged
[3] https://lore.kernel.org/kvm/20230718105542.4138-1-yi.l.liu@intel.com/
[4] https://lore.kernel.org/kvm/20230525095939.37ddb8ce.alex.williamson@redhat.com/
[5] https://lore.kernel.org/linux-iommu/20230511143844.22693-1-yi.l.liu@intel.com/
[6] https://lore.kernel.org/linux-iommu/20230511145110.27707-1-yi.l.liu@intel.com/#t
=======

* 'v6.6/vfio/cdev' of https://github.com/awilliam/linux-vfio: (36 commits)
  docs: vfio: Add vfio device cdev description
  vfio: Compile vfio_group infrastructure optionally
  vfio: Move the IOMMU_CAP_CACHE_COHERENCY check in __vfio_register_dev()
  vfio: Add VFIO_DEVICE_[AT|DE]TACH_IOMMUFD_PT
  vfio: Add VFIO_DEVICE_BIND_IOMMUFD
  vfio: Avoid repeated user pointer cast in vfio_device_fops_unl_ioctl()
  iommufd: Add iommufd_ctx_from_fd()
  vfio: Test kvm pointer in _vfio_device_get_kvm_safe()
  vfio: Add cdev for vfio_device
  vfio: Move device_del() before waiting for the last vfio_device registration refcount
  vfio: Move vfio_device_group_unregister() to be the first operation in unregister
  vfio-iommufd: Add detach_ioas support for emulated VFIO devices
  iommufd/device: Add iommufd_access_detach() API
  vfio-iommufd: Add detach_ioas support for physical VFIO devices
  vfio: Record devid in vfio_device_file
  vfio-iommufd: Split bind/attach into two steps
  vfio-iommufd: Move noiommu compat validation out of vfio_iommufd_bind()
  vfio: Make vfio_df_open() single open for device cdev path
  vfio: Add cdev_device_open_cnt to vfio_group
  vfio: Block device access via device fd until device is opened
  vfio: Pass struct vfio_device_file * to vfio_device_open/close()
  kvm/vfio: Accept vfio device file from userspace
  kvm/vfio: Prepare for accepting vfio device fd
  vfio: Accept vfio device file in the KVM facing kAPI
  vfio: Refine vfio file kAPIs for KVM
  vfio: Allocate per device file structure
  vfio/pci: Allow passing zero-length fd array in VFIO_DEVICE_PCI_HOT_RESET
  vfio/pci: Copy hot-reset device info to userspace in the devices loop
  vfio/pci: Extend VFIO_DEVICE_GET_PCI_HOT_RESET_INFO for vfio device cdev
  vfio: Add helper to search vfio_device in a dev_set
  ...