Merge tag 'for-linus-iommufd' of git://git.kernel.org/pub/scm/linux/kernel/git/jgg/iommufd

Pull iommufd implementation from Jason Gunthorpe:
 "iommufd is the user API to control the IOMMU subsystem as it relates
  to managing IO page tables that point at user space memory.

  It takes over from drivers/vfio/vfio_iommu_type1.c (aka the VFIO
  container) which is the VFIO specific interface for a similar idea.

  We see a broad need for extended features, some being highly IOMMU
  device specific:
   - Binding iommu_domain's to PASID/SSID
   - Userspace IO page tables, for ARM, x86 and S390
   - Kernel bypassed invalidation of user page tables
   - Re-use of the KVM page table in the IOMMU
   - Dirty page tracking in the IOMMU
   - Runtime Increase/Decrease of IOPTE size
   - PRI support with faults resolved in userspace

  Many of these HW features exist to support VM use cases - for instance
  the combination of PASID, PRI and Userspace IO Page Tables allows an
  implementation of DMA Shared Virtual Addressing (vSVA) within a guest.
  Dirty tracking enables VM live migration with SRIOV devices and PASID
  support allow creating "scalable IOV" devices, among other things.

  As these features are fundamental to a VM platform they need to be
  uniformly exposed to all the driver families that do DMA into VMs,
  which is currently VFIO and VDPA"

For more background, see the extended explanations in Jason's pull request:

  https://lore.kernel.org/lkml/Y5dzTU8dlmXTbzoJ@nvidia.com/

* tag 'for-linus-iommufd' of git://git.kernel.org/pub/scm/linux/kernel/git/jgg/iommufd: (62 commits)
  iommufd: Change the order of MSI setup
  iommufd: Improve a few unclear bits of code
  iommufd: Fix comment typos
  vfio: Move vfio group specific code into group.c
  vfio: Refactor dma APIs for emulated devices
  vfio: Wrap vfio group module init/clean code into helpers
  vfio: Refactor vfio_device open and close
  vfio: Make vfio_device_open() truly device specific
  vfio: Swap order of vfio_device_container_register() and open_device()
  vfio: Set device->group in helper function
  vfio: Create wrappers for group register/unregister
  vfio: Move the sanity check of the group to vfio_create_group()
  vfio: Simplify vfio_create_group()
  iommufd: Allow iommufd to supply /dev/vfio/vfio
  vfio: Make vfio_container optionally compiled
  vfio: Move container related MODULE_ALIAS statements into container.c
  vfio-iommufd: Support iommufd for emulated VFIO devices
  vfio-iommufd: Support iommufd for physical VFIO devices
  vfio-iommufd: Allow iommufd to be used in place of a container fd
  vfio: Use IOMMU_CAP_ENFORCE_CACHE_COHERENCY for vfio_file_enforced_coherent()
  ...

3 files changed, 225 insertions, 0 deletions

diff --git a/Documentation/userspace-api/index.rst b/Documentation/userspace-api/index.rst
index c78da9ce0ec4..f16337bdb852 100644
--- a/Documentation/userspace-api/index.rst
+++ b/Documentation/userspace-api/index.rst
@@ -25,6 +25,7 @@ place where this information is gathered.
    ebpf/index
    ioctl/index
    iommu
+   iommufd
    media/index
    netlink/index
    sysfs-platform_profile
diff --git a/Documentation/userspace-api/ioctl/ioctl-number.rst b/Documentation/userspace-api/ioctl/ioctl-number.rst
index 5f81e2a24a5c..eb045fc495a4 100644
--- a/Documentation/userspace-api/ioctl/ioctl-number.rst
+++ b/Documentation/userspace-api/ioctl/ioctl-number.rst
@@ -105,6 +105,7 @@ Code  Seq#    Include File                                           Comments
 '8'   all                                                            SNP8023 advanced NIC card
                                                                      <mailto:mcr@solidum.com>
 ';'   64-7F  linux/vfio.h
+';'   80-FF  linux/iommufd.h
 '='   00-3f  uapi/linux/ptp_clock.h                                  <mailto:richardcochran@gmail.com>
 '@'   00-0F  linux/radeonfb.h                                        conflict!
 '@'   00-0F  drivers/video/aty/aty128fb.c                            conflict!
diff --git a/Documentation/userspace-api/iommufd.rst b/Documentation/userspace-api/iommufd.rst
new file mode 100644
index 000000000000..79dd9eb51587
--- /dev/null
+++ b/Documentation/userspace-api/iommufd.rst
@@ -0,0 +1,223 @@
+.. SPDX-License-Identifier: GPL-2.0+
+
+=======
+IOMMUFD
+=======
+
+:Author: Jason Gunthorpe
+:Author: Kevin Tian
+
+Overview
+========
+
+IOMMUFD is the user API to control the IOMMU subsystem as it relates to managing
+IO page tables from userspace using file descriptors. It intends to be general
+and consumable by any driver that wants to expose DMA to userspace. These
+drivers are eventually expected to deprecate any internal IOMMU logic
+they may already/historically implement (e.g. vfio_iommu_type1.c).
+
+At minimum iommufd provides universal support of managing I/O address spaces and
+I/O page tables for all IOMMUs, with room in the design to add non-generic
+features to cater to specific hardware functionality.
+
+In this context the capital letter (IOMMUFD) refers to the subsystem while the
+small letter (iommufd) refers to the file descriptors created via /dev/iommu for
+use by userspace.
+
+Key Concepts
+============
+
+User Visible Objects
+--------------------
+
+Following IOMMUFD objects are exposed to userspace:
+
+- IOMMUFD_OBJ_IOAS, representing an I/O address space (IOAS), allowing map/unmap
+  of user space memory into ranges of I/O Virtual Address (IOVA).
+
+  The IOAS is a functional replacement for the VFIO container, and like the VFIO
+  container it copies an IOVA map to a list of iommu_domains held within it.
+
+- IOMMUFD_OBJ_DEVICE, representing a device that is bound to iommufd by an
+  external driver.
+
+- IOMMUFD_OBJ_HW_PAGETABLE, representing an actual hardware I/O page table
+  (i.e. a single struct iommu_domain) managed by the iommu driver.
+
+  The IOAS has a list of HW_PAGETABLES that share the same IOVA mapping and
+  it will synchronize its mapping with each member HW_PAGETABLE.
+
+All user-visible objects are destroyed via the IOMMU_DESTROY uAPI.
+
+The diagram below shows relationship between user-visible objects and kernel
+datastructures (external to iommufd), with numbers referred to operations
+creating the objects and links::
+
+  _________________________________________________________
+ |                         iommufd                         |
+ |       [1]                                               |
+ |  _________________                                      |
+ | |                 |                                     |
+ | |                 |                                     |
+ | |                 |                                     |
+ | |                 |                                     |
+ | |                 |                                     |
+ | |                 |                                     |
+ | |                 |        [3]                 [2]      |
+ | |                 |    ____________         __________  |
+ | |      IOAS       |<--|            |<------|          | |
+ | |                 |   |HW_PAGETABLE|       |  DEVICE  | |
+ | |                 |   |____________|       |__________| |
+ | |                 |         |                   |       |
+ | |                 |         |                   |       |
+ | |                 |         |                   |       |
+ | |                 |         |                   |       |
+ | |                 |         |                   |       |
+ | |_________________|         |                   |       |
+ |         |                   |                   |       |
+ |_________|___________________|___________________|_______|
+           |                   |                   |
+           |              _____v______      _______v_____
+           | PFN storage |            |    |             |
+           |------------>|iommu_domain|    |struct device|
+                         |____________|    |_____________|
+
+1. IOMMUFD_OBJ_IOAS is created via the IOMMU_IOAS_ALLOC uAPI. An iommufd can
+   hold multiple IOAS objects. IOAS is the most generic object and does not
+   expose interfaces that are specific to single IOMMU drivers. All operations
+   on the IOAS must operate equally on each of the iommu_domains inside of it.
+
+2. IOMMUFD_OBJ_DEVICE is created when an external driver calls the IOMMUFD kAPI
+   to bind a device to an iommufd. The driver is expected to implement a set of
+   ioctls to allow userspace to initiate the binding operation. Successful
+   completion of this operation establishes the desired DMA ownership over the
+   device. The driver must also set the driver_managed_dma flag and must not
+   touch the device until this operation succeeds.
+
+3. IOMMUFD_OBJ_HW_PAGETABLE is created when an external driver calls the IOMMUFD
+   kAPI to attach a bound device to an IOAS. Similarly the external driver uAPI
+   allows userspace to initiate the attaching operation. If a compatible
+   pagetable already exists then it is reused for the attachment. Otherwise a
+   new pagetable object and iommu_domain is created. Successful completion of
+   this operation sets up the linkages among IOAS, device and iommu_domain. Once
+   this completes the device could do DMA.
+
+   Every iommu_domain inside the IOAS is also represented to userspace as a
+   HW_PAGETABLE object.
+
+   .. note::
+
+      Future IOMMUFD updates will provide an API to create and manipulate the
+      HW_PAGETABLE directly.
+
+A device can only bind to an iommufd due to DMA ownership claim and attach to at
+most one IOAS object (no support of PASID yet).
+
+Kernel Datastructure
+--------------------
+
+User visible objects are backed by following datastructures:
+
+- iommufd_ioas for IOMMUFD_OBJ_IOAS.
+- iommufd_device for IOMMUFD_OBJ_DEVICE.
+- iommufd_hw_pagetable for IOMMUFD_OBJ_HW_PAGETABLE.
+
+Several terminologies when looking at these datastructures:
+
+- Automatic domain - refers to an iommu domain created automatically when
+  attaching a device to an IOAS object. This is compatible to the semantics of
+  VFIO type1.
+
+- Manual domain - refers to an iommu domain designated by the user as the
+  target pagetable to be attached to by a device. Though currently there are
+  no uAPIs to directly create such domain, the datastructure and algorithms
+  are ready for handling that use case.
+
+- In-kernel user - refers to something like a VFIO mdev that is using the
+  IOMMUFD access interface to access the IOAS. This starts by creating an
+  iommufd_access object that is similar to the domain binding a physical device
+  would do. The access object will then allow converting IOVA ranges into struct
+  page * lists, or doing direct read/write to an IOVA.
+
+iommufd_ioas serves as the metadata datastructure to manage how IOVA ranges are
+mapped to memory pages, composed of:
+
+- struct io_pagetable holding the IOVA map
+- struct iopt_area's representing populated portions of IOVA
+- struct iopt_pages representing the storage of PFNs
+- struct iommu_domain representing the IO page table in the IOMMU
+- struct iopt_pages_access representing in-kernel users of PFNs
+- struct xarray pinned_pfns holding a list of pages pinned by in-kernel users
+
+Each iopt_pages represents a logical linear array of full PFNs. The PFNs are
+ultimately derived from userspace VAs via an mm_struct. Once they have been
+pinned the PFNs are stored in IOPTEs of an iommu_domain or inside the pinned_pfns
+xarray if they have been pinned through an iommufd_access.
+
+PFN have to be copied between all combinations of storage locations, depending
+on what domains are present and what kinds of in-kernel "software access" users
+exist. The mechanism ensures that a page is pinned only once.
+
+An io_pagetable is composed of iopt_areas pointing at iopt_pages, along with a
+list of iommu_domains that mirror the IOVA to PFN map.
+
+Multiple io_pagetable-s, through their iopt_area-s, can share a single
+iopt_pages which avoids multi-pinning and double accounting of page
+consumption.
+
+iommufd_ioas is sharable between subsystems, e.g. VFIO and VDPA, as long as
+devices managed by different subsystems are bound to a same iommufd.
+
+IOMMUFD User API
+================
+
+.. kernel-doc:: include/uapi/linux/iommufd.h
+
+IOMMUFD Kernel API
+==================
+
+The IOMMUFD kAPI is device-centric with group-related tricks managed behind the
+scene. This allows the external drivers calling such kAPI to implement a simple
+device-centric uAPI for connecting its device to an iommufd, instead of
+explicitly imposing the group semantics in its uAPI as VFIO does.
+
+.. kernel-doc:: drivers/iommu/iommufd/device.c
+   :export:
+
+.. kernel-doc:: drivers/iommu/iommufd/main.c
+   :export:
+
+VFIO and IOMMUFD
+----------------
+
+Connecting a VFIO device to iommufd can be done in two ways.
+
+First is a VFIO compatible way by directly implementing the /dev/vfio/vfio
+container IOCTLs by mapping them into io_pagetable operations. Doing so allows
+the use of iommufd in legacy VFIO applications by symlinking /dev/vfio/vfio to
+/dev/iommufd or extending VFIO to SET_CONTAINER using an iommufd instead of a
+container fd.
+
+The second approach directly extends VFIO to support a new set of device-centric
+user API based on aforementioned IOMMUFD kernel API. It requires userspace
+change but better matches the IOMMUFD API semantics and easier to support new
+iommufd features when comparing it to the first approach.
+
+Currently both approaches are still work-in-progress.
+
+There are still a few gaps to be resolved to catch up with VFIO type1, as
+documented in iommufd_vfio_check_extension().
+
+Future TODOs
+============
+
+Currently IOMMUFD supports only kernel-managed I/O page table, similar to VFIO
+type1. New features on the radar include:
+
+ - Binding iommu_domain's to PASID/SSID
+ - Userspace page tables, for ARM, x86 and S390
+ - Kernel bypass'd invalidation of user page tables
+ - Re-use of the KVM page table in the IOMMU
+ - Dirty page tracking in the IOMMU
+ - Runtime Increase/Decrease of IOPTE size
+ - PRI support with faults resolved in userspace