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_HWPT_PAGING, representing an actual hardware I/O page table (i.e. a single struct iommu_domain) managed by the iommu driver. “PAGING” primarly indicates this type of HWPT should be linked to an IOAS. It also indicates that it is backed by an iommu_domain with __IOMMU_DOMAIN_PAGING feature flag. This can be either an UNMANAGED stage-1 domain for a device running in the user space, or a nesting parent stage-2 domain for mappings from guest-level physical addresses to host-level physical addresses.

The IOAS has a list of HWPT_PAGINGs that share the same IOVA mapping and it will synchronize its mapping with each member HWPT_PAGING.
IOMMUFD_OBJ_HWPT_NESTED, representing an actual hardware I/O page table (i.e. a single struct iommu_domain) managed by user space (e.g. guest OS). “NESTED” indicates that this type of HWPT should be linked to an HWPT_PAGING. It also indicates that it is backed by an iommu_domain that has a type of IOMMU_DOMAIN_NESTED. This must be a stage-1 domain for a device running in the user space (e.g. in a guest VM enabling the IOMMU nested translation feature.) As such, it must be created with a given nesting parent stage-2 domain to associate to. This nested stage-1 page table managed by the user space usually has mappings from guest-level I/O virtual addresses to guest- level physical addresses.
IOMMUFD_OBJ_VIOMMU, representing a slice of the physical IOMMU instance, passed to or shared with a VM. It may be some HW-accelerated virtualization features and some SW resources used by the VM. For examples:
- Security namespace for guest owned ID, e.g. guest-controlled cache tags
- Non-device-affiliated event reporting, e.g. invalidation queue errors
- Access to a sharable nesting parent pagetable across physical IOMMUs
- Virtualization of various platforms IDs, e.g. RIDs and others
- Delivery of paravirtualized invalidation
- Direct assigned invalidation queues
- Direct assigned interrupts
Such a vIOMMU object generally has the access to a nesting parent pagetable to support some HW-accelerated virtualization features. So, a vIOMMU object must be created given a nesting parent HWPT_PAGING object, and then it would encapsulate that HWPT_PAGING object. Therefore, a vIOMMU object can be used to allocate an HWPT_NESTED object in place of the encapsulated HWPT_PAGING.

Note

The name “vIOMMU” isn’t necessarily identical to a virtualized IOMMU in a VM. A VM can have one giant virtualized IOMMU running on a machine having multiple physical IOMMUs, in which case the VMM will dispatch the requests or configurations from this single virtualized IOMMU instance to multiple vIOMMU objects created for individual slices of different physical IOMMUs. In other words, a vIOMMU object is always a representation of one physical IOMMU, not necessarily of a virtualized IOMMU. For VMMs that want the full virtualization features from physical IOMMUs, it is suggested to build the same number of virtualized IOMMUs as the number of physical IOMMUs, so the passed-through devices would be connected to their own virtualized IOMMUs backed by corresponding vIOMMU objects, in which case a guest OS would do the “dispatch” naturally instead of VMM trappings.
IOMMUFD_OBJ_VDEVICE, representing a virtual device for an IOMMUFD_OBJ_DEVICE against an IOMMUFD_OBJ_VIOMMU. This virtual device holds the device’s virtual information or attributes (related to the vIOMMU) in a VM. An immediate vDATA example can be the virtual ID of the device on a vIOMMU, which is a unique ID that VMM assigns to the device for a translation channel/port of the vIOMMU, e.g. vSID of ARM SMMUv3, vDeviceID of AMD IOMMU, and vRID of Intel VT-d to a Context Table. Potential use cases of some advanced security information can be forwarded via this object too, such as security level or realm information in a Confidential Compute Architecture. A VMM should create a vDEVICE object to forward all the device information in a VM, when it connects a device to a vIOMMU, which is a separate ioctl call from attaching the same device to an HWPT_PAGING that the vIOMMU holds.

All user-visible objects are destroyed via the IOMMU_DESTROY uAPI.

The diagrams below show relationships between user-visible objects and kernel datastructures (external to iommufd), with numbers referred to operations creating the objects and links:

 _______________________________________________________________________
|                      iommufd (HWPT_PAGING only)                       |
|                                                                       |
|        [1]                  [3]                                [2]    |
|  ________________      _____________                        ________  |
| |                |    |             |                      |        | |
| |      IOAS      |<---| HWPT_PAGING |<---------------------| DEVICE | |
| |________________|    |_____________|                      |________| |
|         |                    |                                  |     |
|_________|____________________|__________________________________|_____|
          |                    |                                  |
          |              ______v_____                          ___v__
          | PFN storage |  (paging)  |                        |struct|
          |------------>|iommu_domain|<-----------------------|device|
                        |____________|                        |______|

 _______________________________________________________________________
|                      iommufd (with HWPT_NESTED)                       |
|                                                                       |
|        [1]                  [3]                [4]             [2]    |
|  ________________      _____________      _____________     ________  |
| |                |    |             |    |             |   |        | |
| |      IOAS      |<---| HWPT_PAGING |<---| HWPT_NESTED |<--| DEVICE | |
| |________________|    |_____________|    |_____________|   |________| |
|         |                    |                  |               |     |
|_________|____________________|__________________|_______________|_____|
          |                    |                  |               |
          |              ______v_____       ______v_____       ___v__
          | PFN storage |  (paging)  |     |  (nested)  |     |struct|
          |------------>|iommu_domain|<----|iommu_domain|<----|device|
                        |____________|     |____________|     |______|

 _______________________________________________________________________
|                      iommufd (with vIOMMU/vDEVICE)                    |
|                                                                       |
|                             [5]                [6]                    |
|                        _____________      _____________               |
|                       |             |    |             |              |
|      |----------------|    vIOMMU   |<---|   vDEVICE   |<----|        |
|      |                |             |    |_____________|     |        |
|      |                |             |                        |        |
|      |      [1]       |             |          [4]           | [2]    |
|      |     ______     |             |     _____________     _|______  |
|      |    |      |    |     [3]     |    |             |   |        | |
|      |    | IOAS |<---|(HWPT_PAGING)|<---| HWPT_NESTED |<--| DEVICE | |
|      |    |______|    |_____________|    |_____________|   |________| |
|      |        |              |                  |               |     |
|______|________|______________|__________________|_______________|_____|
       |        |              |                  |               |
 ______v_____   |        ______v_____       ______v_____       ___v__
|   struct   |  |  PFN  |  (paging)  |     |  (nested)  |     |struct|
|iommu_device|  |------>|iommu_domain|<----|iommu_domain|<----|device|
|____________|   storage|____________|     |____________|     |______|

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.
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.
IOMMUFD_OBJ_HWPT_PAGING can be created in two ways:
- IOMMUFD_OBJ_HWPT_PAGING is automatically 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 member HWPT_PAGING object exists in the IOAS’s HWPT_PAGING list, then it will be reused. Otherwise a new HWPT_PAGING that represents an iommu_domain to userspace will be created, and then added to the list. Successful completion of this operation sets up the linkages among IOAS, device and iommu_domain. Once this completes the device could do DMA.
- IOMMUFD_OBJ_HWPT_PAGING can be manually created via the IOMMU_HWPT_ALLOC uAPI, provided an ioas_id via @pt_id to associate the new HWPT_PAGING to the corresponding IOAS object. The benefit of this manual allocation is to allow allocation flags (defined in enum iommufd_hwpt_alloc_flags), e.g. it allocates a nesting parent HWPT_PAGING if the IOMMU_HWPT_ALLOC_NEST_PARENT flag is set.
IOMMUFD_OBJ_HWPT_NESTED can be only manually created via the IOMMU_HWPT_ALLOC uAPI, provided an hwpt_id or a viommu_id of a vIOMMU object encapsulating a nesting parent HWPT_PAGING via @pt_id to associate the new HWPT_NESTED object to the corresponding HWPT_PAGING object. The associating HWPT_PAGING object must be a nesting parent manually allocated via the same uAPI previously with an IOMMU_HWPT_ALLOC_NEST_PARENT flag, otherwise the allocation will fail. The allocation will be further validated by the IOMMU driver to ensure that the nesting parent domain and the nested domain being allocated are compatible. Successful completion of this operation sets up linkages among IOAS, device, and iommu_domains. Once this completes the device could do DMA via a 2-stage translation, a.k.a nested translation. Note that multiple HWPT_NESTED objects can be allocated by (and then associated to) the same nesting parent.

Note

Either a manual IOMMUFD_OBJ_HWPT_PAGING or an IOMMUFD_OBJ_HWPT_NESTED is created via the same IOMMU_HWPT_ALLOC uAPI. The difference is at the type of the object passed in via the @pt_id field of struct iommufd_hwpt_alloc.
IOMMUFD_OBJ_VIOMMU can be only manually created via the IOMMU_VIOMMU_ALLOC uAPI, provided a dev_id (for the device’s physical IOMMU to back the vIOMMU) and an hwpt_id (to associate the vIOMMU to a nesting parent HWPT_PAGING). The iommufd core will link the vIOMMU object to the struct iommu_device that the struct device is behind. And an IOMMU driver can implement a viommu_alloc op to allocate its own vIOMMU data structure embedding the core-level structure iommufd_viommu and some driver-specific data. If necessary, the driver can also configure its HW virtualization feature for that vIOMMU (and thus for the VM). Successful completion of this operation sets up the linkages between the vIOMMU object and the HWPT_PAGING, then this vIOMMU object can be used as a nesting parent object to allocate an HWPT_NESTED object described above.
IOMMUFD_OBJ_VDEVICE can be only manually created via the IOMMU_VDEVICE_ALLOC uAPI, provided a viommu_id for an iommufd_viommu object and a dev_id for an iommufd_device object. The vDEVICE object will be the binding between these two parent objects. Another @virt_id will be also set via the uAPI providing the iommufd core an index to store the vDEVICE object to a vDEVICE array per vIOMMU. If necessary, the IOMMU driver may choose to implement a vdevce_alloc op to init its HW for virtualization feature related to a vDEVICE. Successful completion of this operation sets up the linkages between vIOMMU and device.

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_hwpt_paging for IOMMUFD_OBJ_HWPT_PAGING.
iommufd_hwpt_nested for IOMMUFD_OBJ_HWPT_NESTED.
iommufd_viommu for IOMMUFD_OBJ_VIOMMU.
iommufd_vdevice for IOMMUFD_OBJ_VDEVICE.

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 shareable between subsystems, e.g. VFIO and VDPA, as long as devices managed by different subsystems are bound to a same iommufd.

IOMMUFD User API¶

General ioctl format

The ioctl interface follows a general format to allow for extensibility. Each ioctl is passed in a structure pointer as the argument providing the size of the structure in the first u32. The kernel checks that any structure space beyond what it understands is 0. This allows userspace to use the backward compatible portion while consistently using the newer, larger, structures.

ioctls use a standard meaning for common errnos:

ENOTTY: The IOCTL number itself is not supported at all

E2BIG: The IOCTL number is supported, but the provided structure has non-zero in a part the kernel does not understand.

EOPNOTSUPP: The IOCTL number is supported, and the structure is understood, however a known field has a value the kernel does not understand or support.

EINVAL: Everything about the IOCTL was understood, but a field is not correct.

ENOENT: An ID or IOVA provided does not exist.

ENOMEM: Out of memory.

EOVERFLOW: Mathematics overflowed.

As well as additional errnos, within specific ioctls.

struct iommu_destroy¶: ioctl(IOMMU_DESTROY)

Definition:

struct iommu_destroy {
    __u32 size;
    __u32 id;
};

Members

size: sizeof(struct iommu_destroy)
id: iommufd object ID to destroy. Can be any destroyable object type.

Description

Destroy any object held within iommufd.

struct iommu_ioas_alloc¶: ioctl(IOMMU_IOAS_ALLOC)

Definition:

struct iommu_ioas_alloc {
    __u32 size;
    __u32 flags;
    __u32 out_ioas_id;
};

Members

size: sizeof(struct iommu_ioas_alloc)
flags: Must be 0
out_ioas_id: Output IOAS ID for the allocated object

Description

Allocate an IO Address Space (IOAS) which holds an IO Virtual Address (IOVA) to memory mapping.

struct iommu_iova_range¶: ioctl(IOMMU_IOVA_RANGE)

Definition:

struct iommu_iova_range {
    __aligned_u64 start;
    __aligned_u64 last;
};

Members

start: First IOVA
last: Inclusive last IOVA

Description

An interval in IOVA space.

struct iommu_ioas_iova_ranges¶: ioctl(IOMMU_IOAS_IOVA_RANGES)

Definition:

struct iommu_ioas_iova_ranges {
    __u32 size;
    __u32 ioas_id;
    __u32 num_iovas;
    __u32 __reserved;
    __aligned_u64 allowed_iovas;
    __aligned_u64 out_iova_alignment;
};

Members

size: sizeof(struct iommu_ioas_iova_ranges)
ioas_id: IOAS ID to read ranges from
num_iovas: Input/Output total number of ranges in the IOAS
__reserved: Must be 0
allowed_iovas: Pointer to the output array of struct iommu_iova_range
out_iova_alignment: Minimum alignment required for mapping IOVA

Description

Query an IOAS for ranges of allowed IOVAs. Mapping IOVA outside these ranges is not allowed. num_iovas will be set to the total number of iovas and the allowed_iovas[] will be filled in as space permits.

The allowed ranges are dependent on the HW path the DMA operation takes, and can change during the lifetime of the IOAS. A fresh empty IOAS will have a full range, and each attached device will narrow the ranges based on that device’s HW restrictions. Detaching a device can widen the ranges. Userspace should query ranges after every attach/detach to know what IOVAs are valid for mapping.

On input num_iovas is the length of the allowed_iovas array. On output it is the total number of iovas filled in. The ioctl will return -EMSGSIZE and set num_iovas to the required value if num_iovas is too small. In this case the caller should allocate a larger output array and re-issue the ioctl.

out_iova_alignment returns the minimum IOVA alignment that can be given to IOMMU_IOAS_MAP/COPY. IOVA’s must satisfy:

starting_iova % out_iova_alignment == 0
(starting_iova + length) % out_iova_alignment == 0

out_iova_alignment can be 1 indicating any IOVA is allowed. It cannot be higher than the system PAGE_SIZE.

struct iommu_ioas_allow_iovas¶: ioctl(IOMMU_IOAS_ALLOW_IOVAS)

Definition:

struct iommu_ioas_allow_iovas {
    __u32 size;
    __u32 ioas_id;
    __u32 num_iovas;
    __u32 __reserved;
    __aligned_u64 allowed_iovas;
};

Members

size: sizeof(struct iommu_ioas_allow_iovas)
ioas_id: IOAS ID to allow IOVAs from
num_iovas: Input/Output total number of ranges in the IOAS
__reserved: Must be 0
allowed_iovas: Pointer to array of struct iommu_iova_range

Description

Ensure a range of IOVAs are always available for allocation. If this call succeeds then IOMMU_IOAS_IOVA_RANGES will never return a list of IOVA ranges that are narrower than the ranges provided here. This call will fail if IOMMU_IOAS_IOVA_RANGES is currently narrower than the given ranges.

When an IOAS is first created the IOVA_RANGES will be maximally sized, and as devices are attached the IOVA will narrow based on the device restrictions. When an allowed range is specified any narrowing will be refused, ie device attachment can fail if the device requires limiting within the allowed range.

Automatic IOVA allocation is also impacted by this call. MAP will only allocate within the allowed IOVAs if they are present.

This call replaces the entire allowed list with the given list.

enum iommufd_ioas_map_flags¶: Flags for map and copy

Constants

IOMMU_IOAS_MAP_FIXED_IOVA: If clear the kernel will compute an appropriate IOVA to place the mapping at
IOMMU_IOAS_MAP_WRITEABLE: DMA is allowed to write to this mapping
IOMMU_IOAS_MAP_READABLE: DMA is allowed to read from this mapping

struct iommu_ioas_map¶: ioctl(IOMMU_IOAS_MAP)

Definition:

struct iommu_ioas_map {
    __u32 size;
    __u32 flags;
    __u32 ioas_id;
    __u32 __reserved;
    __aligned_u64 user_va;
    __aligned_u64 length;
    __aligned_u64 iova;
};

Members

size: sizeof(struct iommu_ioas_map)
flags: Combination of enum iommufd_ioas_map_flags
ioas_id: IOAS ID to change the mapping of
__reserved: Must be 0
user_va: Userspace pointer to start mapping from
length: Number of bytes to map
iova: IOVA the mapping was placed at. If IOMMU_IOAS_MAP_FIXED_IOVA is set then this must be provided as input.

Description

Set an IOVA mapping from a user pointer. If FIXED_IOVA is specified then the mapping will be established at iova, otherwise a suitable location based on the reserved and allowed lists will be automatically selected and returned in iova.

If IOMMU_IOAS_MAP_FIXED_IOVA is specified then the iova range must currently be unused, existing IOVA cannot be replaced.

struct iommu_ioas_map_file¶: ioctl(IOMMU_IOAS_MAP_FILE)

Definition:

struct iommu_ioas_map_file {
    __u32 size;
    __u32 flags;
    __u32 ioas_id;
    __s32 fd;
    __aligned_u64 start;
    __aligned_u64 length;
    __aligned_u64 iova;
};

Members

size: sizeof(struct iommu_ioas_map_file)
flags: same as for iommu_ioas_map
ioas_id: same as for iommu_ioas_map
fd: the memfd to map
start: byte offset from start of file to map from
length: same as for iommu_ioas_map
iova: same as for iommu_ioas_map

Description

Set an IOVA mapping from a memfd file. All other arguments and semantics match those of IOMMU_IOAS_MAP.

struct iommu_ioas_copy¶: ioctl(IOMMU_IOAS_COPY)

Definition:

struct iommu_ioas_copy {
    __u32 size;
    __u32 flags;
    __u32 dst_ioas_id;
    __u32 src_ioas_id;
    __aligned_u64 length;
    __aligned_u64 dst_iova;
    __aligned_u64 src_iova;
};

Members

size: sizeof(struct iommu_ioas_copy)
flags: Combination of enum iommufd_ioas_map_flags
dst_ioas_id: IOAS ID to change the mapping of
src_ioas_id: IOAS ID to copy from
length: Number of bytes to copy and map
dst_iova: IOVA the mapping was placed at. If IOMMU_IOAS_MAP_FIXED_IOVA is set then this must be provided as input.
src_iova: IOVA to start the copy

Description

Copy an already existing mapping from src_ioas_id and establish it in dst_ioas_id. The src iova/length must exactly match a range used with IOMMU_IOAS_MAP.

This may be used to efficiently clone a subset of an IOAS to another, or as a kind of ‘cache’ to speed up mapping. Copy has an efficiency advantage over establishing equivalent new mappings, as internal resources are shared, and the kernel will pin the user memory only once.

struct iommu_ioas_unmap¶: ioctl(IOMMU_IOAS_UNMAP)

Definition:

struct iommu_ioas_unmap {
    __u32 size;
    __u32 ioas_id;
    __aligned_u64 iova;
    __aligned_u64 length;
};

Members

size: sizeof(struct iommu_ioas_unmap)
ioas_id: IOAS ID to change the mapping of
iova: IOVA to start the unmapping at
length: Number of bytes to unmap, and return back the bytes unmapped

Description

Unmap an IOVA range. The iova/length must be a superset of a previously mapped range used with IOMMU_IOAS_MAP or IOMMU_IOAS_COPY. Splitting or truncating ranges is not allowed. The values 0 to U64_MAX will unmap everything.

enum iommufd_option¶: ioctl(IOMMU_OPTION_RLIMIT_MODE) and ioctl(IOMMU_OPTION_HUGE_PAGES)

Constants

IOMMU_OPTION_RLIMIT_MODE

Change how RLIMIT_MEMLOCK accounting works. The caller must have privilege to invoke this. Value 0 (default) is user based accounting, 1 uses process based accounting. Global option, object_id must be 0

IOMMU_OPTION_HUGE_PAGES

Value 1 (default) allows contiguous pages to be combined when generating iommu mappings. Value 0 disables combining, everything is mapped to PAGE_SIZE. This can be useful for benchmarking. This is a per-IOAS option, the object_id must be the IOAS ID.

enum iommufd_option_ops¶: ioctl(IOMMU_OPTION_OP_SET) and ioctl(IOMMU_OPTION_OP_GET)

Constants

IOMMU_OPTION_OP_SET: Set the option’s value
IOMMU_OPTION_OP_GET: Get the option’s value

struct iommu_option¶: iommu option multiplexer

Definition:

struct iommu_option {
    __u32 size;
    __u32 option_id;
    __u16 op;
    __u16 __reserved;
    __u32 object_id;
    __aligned_u64 val64;
};

Members

size: sizeof(struct iommu_option)
option_id: One of enum iommufd_option
op: One of enum iommufd_option_ops
__reserved: Must be 0
object_id: ID of the object if required
val64: Option value to set or value returned on get

Description

Change a simple option value. This multiplexor allows controlling options on objects. IOMMU_OPTION_OP_SET will load an option and IOMMU_OPTION_OP_GET will return the current value.

enum iommufd_vfio_ioas_op¶: IOMMU_VFIO_IOAS_* ioctls

Constants

IOMMU_VFIO_IOAS_GET: Get the current compatibility IOAS
IOMMU_VFIO_IOAS_SET: Change the current compatibility IOAS
IOMMU_VFIO_IOAS_CLEAR: Disable VFIO compatibility

struct iommu_vfio_ioas¶: ioctl(IOMMU_VFIO_IOAS)

Definition:

struct iommu_vfio_ioas {
    __u32 size;
    __u32 ioas_id;
    __u16 op;
    __u16 __reserved;
};

Members

size: sizeof(struct iommu_vfio_ioas)
ioas_id: For IOMMU_VFIO_IOAS_SET the input IOAS ID to set For IOMMU_VFIO_IOAS_GET will output the IOAS ID
op: One of enum iommufd_vfio_ioas_op
__reserved: Must be 0

Description

The VFIO compatibility support uses a single ioas because VFIO APIs do not support the ID field. Set or Get the IOAS that VFIO compatibility will use. When VFIO_GROUP_SET_CONTAINER is used on an iommufd it will get the compatibility ioas, either by taking what is already set, or auto creating one. From then on VFIO will continue to use that ioas and is not effected by this ioctl. SET or CLEAR does not destroy any auto-created IOAS.

enum iommufd_hwpt_alloc_flags¶: Flags for HWPT allocation

Constants

IOMMU_HWPT_ALLOC_NEST_PARENT: If set, allocate a HWPT that can serve as the parent HWPT in a nesting configuration.
IOMMU_HWPT_ALLOC_DIRTY_TRACKING: Dirty tracking support for device IOMMU is enforced on device attachment
IOMMU_HWPT_FAULT_ID_VALID: The fault_id field of hwpt allocation data is valid.
IOMMU_HWPT_ALLOC_PASID: Requests a domain that can be used with PASID. The domain can be attached to any PASID on the device. Any domain attached to the non-PASID part of the device must also be flagged, otherwise attaching a PASID will blocked. If IOMMU does not support PASID it will return error (-EOPNOTSUPP).

enum iommu_hwpt_vtd_s1_flags¶: Intel VT-d stage-1 page table entry attributes

Constants

IOMMU_VTD_S1_SRE: Supervisor request
IOMMU_VTD_S1_EAFE: Extended access enable
IOMMU_VTD_S1_WPE: Write protect enable

struct iommu_hwpt_vtd_s1¶: Intel VT-d stage-1 page table info (IOMMU_HWPT_DATA_VTD_S1)

Definition:

struct iommu_hwpt_vtd_s1 {
    __aligned_u64 flags;
    __aligned_u64 pgtbl_addr;
    __u32 addr_width;
    __u32 __reserved;
};

Members

flags: Combination of enum iommu_hwpt_vtd_s1_flags
pgtbl_addr: The base address of the stage-1 page table.
addr_width: The address width of the stage-1 page table
__reserved: Must be 0

struct iommu_hwpt_arm_smmuv3¶: ARM SMMUv3 nested STE (IOMMU_HWPT_DATA_ARM_SMMUV3)

Definition:

struct iommu_hwpt_arm_smmuv3 {
    __aligned_le64 ste[2];
};

Members

ste: The first two double words of the user space Stream Table Entry for the translation. Must be little-endian. Allowed fields: (Refer to “5.2 Stream Table Entry” in SMMUv3 HW Spec) - word-0: V, Cfg, S1Fmt, S1ContextPtr, S1CDMax - word-1: EATS, S1DSS, S1CIR, S1COR, S1CSH, S1STALLD

Description

-EIO will be returned if ste is not legal or contains any non-allowed field. Cfg can be used to select a S1, Bypass or Abort configuration. A Bypass nested domain will translate the same as the nesting parent. The S1 will install a Context Descriptor Table pointing at userspace memory translated by the nesting parent.

enum iommu_hwpt_data_type¶: IOMMU HWPT Data Type

Constants

IOMMU_HWPT_DATA_NONE: no data
IOMMU_HWPT_DATA_VTD_S1: Intel VT-d stage-1 page table
IOMMU_HWPT_DATA_ARM_SMMUV3: ARM SMMUv3 Context Descriptor Table

struct iommu_hwpt_alloc¶: ioctl(IOMMU_HWPT_ALLOC)

Definition:

struct iommu_hwpt_alloc {
    __u32 size;
    __u32 flags;
    __u32 dev_id;
    __u32 pt_id;
    __u32 out_hwpt_id;
    __u32 __reserved;
    __u32 data_type;
    __u32 data_len;
    __aligned_u64 data_uptr;
    __u32 fault_id;
    __u32 __reserved2;
};

Members

size: sizeof(struct iommu_hwpt_alloc)
flags: Combination of enum iommufd_hwpt_alloc_flags
dev_id: The device to allocate this HWPT for
pt_id: The IOAS or HWPT or vIOMMU to connect this HWPT to
out_hwpt_id: The ID of the new HWPT
__reserved: Must be 0
data_type: One of enum iommu_hwpt_data_type
data_len: Length of the type specific data
data_uptr: User pointer to the type specific data
fault_id: The ID of IOMMUFD_FAULT object. Valid only if flags field of IOMMU_HWPT_FAULT_ID_VALID is set.
__reserved2: Padding to 64-bit alignment. Must be 0.

Description

Explicitly allocate a hardware page table object. This is the same object type that is returned by iommufd_device_attach() and represents the underlying iommu driver’s iommu_domain kernel object.

A kernel-managed HWPT will be created with the mappings from the given IOAS via the pt_id. The data_type for this allocation must be set to IOMMU_HWPT_DATA_NONE. The HWPT can be allocated as a parent HWPT for a nesting configuration by passing IOMMU_HWPT_ALLOC_NEST_PARENT via flags.

A user-managed nested HWPT will be created from a given vIOMMU (wrapping a parent HWPT) or a parent HWPT via pt_id, in which the parent HWPT must be allocated previously via the same ioctl from a given IOAS (pt_id). In this case, the data_type must be set to a pre-defined type corresponding to an I/O page table type supported by the underlying IOMMU hardware. The device via dev_id and the vIOMMU via pt_id must be associated to the same IOMMU instance.

If the data_type is set to IOMMU_HWPT_DATA_NONE, data_len and data_uptr should be zero. Otherwise, both data_len and data_uptr must be given.

enum iommu_hw_info_vtd_flags¶: Flags for VT-d hw_info

Constants

IOMMU_HW_INFO_VTD_ERRATA_772415_SPR17: If set, disallow read-only mappings on a nested_parent domain. https://www.intel.com/content/www/us/en/content-details/772415/content-details.html

struct iommu_hw_info_vtd¶: Intel VT-d hardware information

Definition:

struct iommu_hw_info_vtd {
    __u32 flags;
    __u32 __reserved;
    __aligned_u64 cap_reg;
    __aligned_u64 ecap_reg;
};

Members

flags: Combination of enum iommu_hw_info_vtd_flags
__reserved: Must be 0
cap_reg: Value of Intel VT-d capability register defined in VT-d spec section 11.4.2 Capability Register.
ecap_reg: Value of Intel VT-d capability register defined in VT-d spec section 11.4.3 Extended Capability Register.

Description

User needs to understand the Intel VT-d specification to decode the register value.

struct iommu_hw_info_arm_smmuv3¶: ARM SMMUv3 hardware information (IOMMU_HW_INFO_TYPE_ARM_SMMUV3)

Definition:

struct iommu_hw_info_arm_smmuv3 {
    __u32 flags;
    __u32 __reserved;
    __u32 idr[6];
    __u32 iidr;
    __u32 aidr;
};

Members

flags: Must be set to 0
__reserved: Must be 0
idr: Implemented features for ARM SMMU Non-secure programming interface
iidr: Information about the implementation and implementer of ARM SMMU, and architecture version supported
aidr: ARM SMMU architecture version

Description

For the details of idr, iidr and aidr, please refer to the chapters from 6.3.1 to 6.3.6 in the SMMUv3 Spec.

This reports the raw HW capability, and not all bits are meaningful to be read by userspace. Only the following fields should be used:

idr[0]: ST_LEVEL, TERM_MODEL, STALL_MODEL, TTENDIAN , CD2L, ASID16, TTF idr[1]: SIDSIZE, SSIDSIZE idr[3]: BBML, RIL idr[5]: VAX, GRAN64K, GRAN16K, GRAN4K

S1P should be assumed to be true if a NESTED HWPT can be created
VFIO/iommufd only support platforms with COHACC, it should be assumed to be true.
ATS is a per-device property. If the VMM describes any devices as ATS capable in ACPI/DT it should set the corresponding idr.

This list may expand in future (eg E0PD, AIE, PBHA, D128, DS etc). It is important that VMMs do not read bits outside the list to allow for compatibility with future kernels. Several features in the SMMUv3 architecture are not currently supported by the kernel for nesting: HTTU, BTM, MPAM and others.

enum iommu_hw_info_type¶: IOMMU Hardware Info Types

Constants

IOMMU_HW_INFO_TYPE_NONE: Used by the drivers that do not report hardware info
IOMMU_HW_INFO_TYPE_INTEL_VTD: Intel VT-d iommu info type
IOMMU_HW_INFO_TYPE_ARM_SMMUV3: ARM SMMUv3 iommu info type

enum iommufd_hw_capabilities¶

Constants

IOMMU_HW_CAP_DIRTY_TRACKING: IOMMU hardware support for dirty tracking If available, it means the following APIs are supported:

IOMMU_HWPT_GET_DIRTY_BITMAP IOMMU_HWPT_SET_DIRTY_TRACKING

struct iommu_hw_info¶: ioctl(IOMMU_GET_HW_INFO)

Definition:

struct iommu_hw_info {
    __u32 size;
    __u32 flags;
    __u32 dev_id;
    __u32 data_len;
    __aligned_u64 data_uptr;
    __u32 out_data_type;
    __u32 __reserved;
    __aligned_u64 out_capabilities;
};

Members

size: sizeof(struct iommu_hw_info)
flags: Must be 0
dev_id: The device bound to the iommufd
data_len: Input the length of a user buffer in bytes. Output the length of data that kernel supports
data_uptr: User pointer to a user-space buffer used by the kernel to fill the iommu type specific hardware information data
out_data_type: Output the iommu hardware info type as defined in the enum iommu_hw_info_type.
__reserved: Must be 0
out_capabilities: Output the generic iommu capability info type as defined in the enum iommu_hw_capabilities.

Description

Query an iommu type specific hardware information data from an iommu behind a given device that has been bound to iommufd. This hardware info data will be used to sync capabilities between the virtual iommu and the physical iommu, e.g. a nested translation setup needs to check the hardware info, so a guest stage-1 page table can be compatible with the physical iommu.

To capture an iommu type specific hardware information data, data_uptr and its length data_len must be provided. Trailing bytes will be zeroed if the user buffer is larger than the data that kernel has. Otherwise, kernel only fills the buffer using the given length in data_len. If the ioctl succeeds, data_len will be updated to the length that kernel actually supports, out_data_type will be filled to decode the data filled in the buffer pointed by data_uptr. Input data_len == zero is allowed.

struct iommu_hwpt_set_dirty_tracking¶: ioctl(IOMMU_HWPT_SET_DIRTY_TRACKING)

Definition:

struct iommu_hwpt_set_dirty_tracking {
    __u32 size;
    __u32 flags;
    __u32 hwpt_id;
    __u32 __reserved;
};

Members

size: sizeof(struct iommu_hwpt_set_dirty_tracking)
flags: Combination of enum iommufd_hwpt_set_dirty_tracking_flags
hwpt_id: HW pagetable ID that represents the IOMMU domain
__reserved: Must be 0

Description

Toggle dirty tracking on an HW pagetable.

enum iommufd_hwpt_get_dirty_bitmap_flags¶: Flags for getting dirty bits

Constants

IOMMU_HWPT_GET_DIRTY_BITMAP_NO_CLEAR: Just read the PTEs without clearing any dirty bits metadata. This flag can be passed in the expectation where the next operation is an unmap of the same IOVA range.

struct iommu_hwpt_get_dirty_bitmap¶: ioctl(IOMMU_HWPT_GET_DIRTY_BITMAP)

Definition:

struct iommu_hwpt_get_dirty_bitmap {
    __u32 size;
    __u32 hwpt_id;
    __u32 flags;
    __u32 __reserved;
    __aligned_u64 iova;
    __aligned_u64 length;
    __aligned_u64 page_size;
    __aligned_u64 data;
};

Members

size: sizeof(struct iommu_hwpt_get_dirty_bitmap)
hwpt_id: HW pagetable ID that represents the IOMMU domain
flags: Combination of enum iommufd_hwpt_get_dirty_bitmap_flags
__reserved: Must be 0
iova: base IOVA of the bitmap first bit
length: IOVA range size
page_size: page size granularity of each bit in the bitmap
data: bitmap where to set the dirty bits. The bitmap bits each represent a page_size which you deviate from an arbitrary iova.

Description

Checking a given IOVA is dirty:

data[(iova / page_size) / 64] & (1ULL << ((iova / page_size) % 64))

Walk the IOMMU pagetables for a given IOVA range to return a bitmap with the dirty IOVAs. In doing so it will also by default clear any dirty bit metadata set in the IOPTE.

enum iommu_hwpt_invalidate_data_type¶: IOMMU HWPT Cache Invalidation Data Type

Constants

IOMMU_HWPT_INVALIDATE_DATA_VTD_S1: Invalidation data for VTD_S1
IOMMU_VIOMMU_INVALIDATE_DATA_ARM_SMMUV3: Invalidation data for ARM SMMUv3

enum iommu_hwpt_vtd_s1_invalidate_flags¶: Flags for Intel VT-d stage-1 cache invalidation

Constants

IOMMU_VTD_INV_FLAGS_LEAF: Indicates whether the invalidation applies to all-levels page structure cache or just the leaf PTE cache.

struct iommu_hwpt_vtd_s1_invalidate¶: Intel VT-d cache invalidation (IOMMU_HWPT_INVALIDATE_DATA_VTD_S1)

Definition:

struct iommu_hwpt_vtd_s1_invalidate {
    __aligned_u64 addr;
    __aligned_u64 npages;
    __u32 flags;
    __u32 __reserved;
};

Members

addr: The start address of the range to be invalidated. It needs to be 4KB aligned.
npages: Number of contiguous 4K pages to be invalidated.
flags: Combination of enum iommu_hwpt_vtd_s1_invalidate_flags
__reserved: Must be 0

Description

The Intel VT-d specific invalidation data for user-managed stage-1 cache invalidation in nested translation. Userspace uses this structure to tell the impacted cache scope after modifying the stage-1 page table.

Invalidating all the caches related to the page table by setting addr to be 0 and npages to be U64_MAX.

The device TLB will be invalidated automatically if ATS is enabled.

struct iommu_viommu_arm_smmuv3_invalidate¶: ARM SMMUv3 cache invalidation (IOMMU_VIOMMU_INVALIDATE_DATA_ARM_SMMUV3)

Definition:

struct iommu_viommu_arm_smmuv3_invalidate {
    __aligned_le64 cmd[2];
};

Members

cmd: 128-bit cache invalidation command that runs in SMMU CMDQ. Must be little-endian.

Description

Supported command list only when passing in a vIOMMU via hwpt_id:: CMDQ_OP_TLBI_NSNH_ALL CMDQ_OP_TLBI_NH_VA CMDQ_OP_TLBI_NH_VAA CMDQ_OP_TLBI_NH_ALL CMDQ_OP_TLBI_NH_ASID CMDQ_OP_ATC_INV CMDQ_OP_CFGI_CD CMDQ_OP_CFGI_CD_ALL

-EIO will be returned if the command is not supported.

struct iommu_hwpt_invalidate¶: ioctl(IOMMU_HWPT_INVALIDATE)

Definition:

struct iommu_hwpt_invalidate {
    __u32 size;
    __u32 hwpt_id;
    __aligned_u64 data_uptr;
    __u32 data_type;
    __u32 entry_len;
    __u32 entry_num;
    __u32 __reserved;
};

Members

size: sizeof(struct iommu_hwpt_invalidate)
hwpt_id: ID of a nested HWPT or a vIOMMU, for cache invalidation
data_uptr: User pointer to an array of driver-specific cache invalidation data.
data_type: One of enum iommu_hwpt_invalidate_data_type, defining the data type of all the entries in the invalidation request array. It should be a type supported by the hwpt pointed by hwpt_id.
entry_len: Length (in bytes) of a request entry in the request array
entry_num: Input the number of cache invalidation requests in the array. Output the number of requests successfully handled by kernel.
__reserved: Must be 0.

Description

Invalidate iommu cache for user-managed page table or vIOMMU. Modifications on a user-managed page table should be followed by this operation, if a HWPT is passed in via hwpt_id. Other caches, such as device cache or descriptor cache can be flushed if a vIOMMU is passed in via the hwpt_id field.

Each ioctl can support one or more cache invalidation requests in the array that has a total size of entry_len * entry_num.

An empty invalidation request array by setting entry_num**==0 is allowed, and **entry_len and data_uptr would be ignored in this case. This can be used to check if the given data_type is supported or not by kernel.

enum iommu_hwpt_pgfault_flags¶: flags for struct iommu_hwpt_pgfault

Constants

IOMMU_PGFAULT_FLAGS_PASID_VALID: The pasid field of the fault data is valid.
IOMMU_PGFAULT_FLAGS_LAST_PAGE: It’s the last fault of a fault group.

enum iommu_hwpt_pgfault_perm¶: perm bits for struct iommu_hwpt_pgfault

Constants

IOMMU_PGFAULT_PERM_READ: request for read permission
IOMMU_PGFAULT_PERM_WRITE: request for write permission
IOMMU_PGFAULT_PERM_EXEC: (PCIE 10.4.1) request with a PASID that has the Execute Requested bit set in PASID TLP Prefix.
IOMMU_PGFAULT_PERM_PRIV: (PCIE 10.4.1) request with a PASID that has the Privileged Mode Requested bit set in PASID TLP Prefix.

struct iommu_hwpt_pgfault¶: iommu page fault data

Definition:

struct iommu_hwpt_pgfault {
    __u32 flags;
    __u32 dev_id;
    __u32 pasid;
    __u32 grpid;
    __u32 perm;
    __u64 addr;
    __u32 length;
    __u32 cookie;
};

Members

flags: Combination of enum iommu_hwpt_pgfault_flags
dev_id: id of the originated device
pasid: Process Address Space ID
grpid: Page Request Group Index
perm: Combination of enum iommu_hwpt_pgfault_perm
addr: Fault address
length: a hint of how much data the requestor is expecting to fetch. For example, if the PRI initiator knows it is going to do a 10MB transfer, it could fill in 10MB and the OS could pre-fault in 10MB of IOVA. It’s default to 0 if there’s no such hint.
cookie: kernel-managed cookie identifying a group of fault messages. The cookie number encoded in the last page fault of the group should be echoed back in the response message.

enum iommufd_page_response_code¶: Return status of fault handlers

Constants

IOMMUFD_PAGE_RESP_SUCCESS: Fault has been handled and the page tables populated, retry the access. This is the “Success” defined in PCI 10.4.2.1.
IOMMUFD_PAGE_RESP_INVALID: Could not handle this fault, don’t retry the access. This is the “Invalid Request” in PCI 10.4.2.1.

struct iommu_hwpt_page_response¶: IOMMU page fault response

Definition:

struct iommu_hwpt_page_response {
    __u32 cookie;
    __u32 code;
};

Members

cookie: The kernel-managed cookie reported in the fault message.
code: One of response code in enum iommufd_page_response_code.

struct iommu_fault_alloc¶: ioctl(IOMMU_FAULT_QUEUE_ALLOC)

Definition:

struct iommu_fault_alloc {
    __u32 size;
    __u32 flags;
    __u32 out_fault_id;
    __u32 out_fault_fd;
};

Members

size: sizeof(struct iommu_fault_alloc)
flags: Must be 0
out_fault_id: The ID of the new FAULT
out_fault_fd: The fd of the new FAULT

Description

Explicitly allocate a fault handling object.

enum iommu_viommu_type¶: Virtual IOMMU Type

Constants

IOMMU_VIOMMU_TYPE_DEFAULT: Reserved for future use
IOMMU_VIOMMU_TYPE_ARM_SMMUV3: ARM SMMUv3 driver specific type

struct iommu_viommu_alloc¶: ioctl(IOMMU_VIOMMU_ALLOC)

Definition:

struct iommu_viommu_alloc {
    __u32 size;
    __u32 flags;
    __u32 type;
    __u32 dev_id;
    __u32 hwpt_id;
    __u32 out_viommu_id;
};

Members

size: sizeof(struct iommu_viommu_alloc)
flags: Must be 0
type: Type of the virtual IOMMU. Must be defined in enum iommu_viommu_type
dev_id: The device’s physical IOMMU will be used to back the virtual IOMMU
hwpt_id: ID of a nesting parent HWPT to associate to
out_viommu_id: Output virtual IOMMU ID for the allocated object

Description

Allocate a virtual IOMMU object, representing the underlying physical IOMMU’s virtualization support that is a security-isolated slice of the real IOMMU HW that is unique to a specific VM. Operations global to the IOMMU are connected to the vIOMMU, such as: - Security namespace for guest owned ID, e.g. guest-controlled cache tags - Non-device-affiliated event reporting, e.g. invalidation queue errors - Access to a sharable nesting parent pagetable across physical IOMMUs - Virtualization of various platforms IDs, e.g. RIDs and others - Delivery of paravirtualized invalidation - Direct assigned invalidation queues - Direct assigned interrupts

struct iommu_vdevice_alloc¶: ioctl(IOMMU_VDEVICE_ALLOC)

Definition:

struct iommu_vdevice_alloc {
    __u32 size;
    __u32 viommu_id;
    __u32 dev_id;
    __u32 out_vdevice_id;
    __aligned_u64 virt_id;
};

Members

size: sizeof(struct iommu_vdevice_alloc)
viommu_id: vIOMMU ID to associate with the virtual device
dev_id: The physical device to allocate a virtual instance on the vIOMMU
out_vdevice_id: Object handle for the vDevice. Pass to IOMMU_DESTORY
virt_id: Virtual device ID per vIOMMU, e.g. vSID of ARM SMMUv3, vDeviceID of AMD IOMMU, and vRID of a nested Intel VT-d to a Context Table

Description

Allocate a virtual device instance (for a physical device) against a vIOMMU. This instance holds the device’s information (related to its vIOMMU) in a VM.

struct iommu_ioas_change_process¶: ioctl(VFIO_IOAS_CHANGE_PROCESS)

Definition:

struct iommu_ioas_change_process {
    __u32 size;
    __u32 __reserved;
};

Members

size: sizeof(struct iommu_ioas_change_process)
__reserved: Must be 0

Description

This transfers pinned memory counts for every memory map in every IOAS in the context to the current process. This only supports maps created with IOMMU_IOAS_MAP_FILE, and returns EINVAL if other maps are present. If the ioctl returns a failure status, then nothing is changed.

This API is useful for transferring operation of a device from one process to another, such as during userland live update.

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.

struct iommufd_device *iommufd_device_bind(struct iommufd_ctx *ictx, struct device *dev, u32 *id)¶: Bind a physical device to an iommu fd

Parameters

struct iommufd_ctx *ictx: iommufd file descriptor
struct device *dev: Pointer to a physical device struct
u32 *id: Output ID number to return to userspace for this device

Description

A successful bind establishes an ownership over the device and returns struct iommufd_device pointer, otherwise returns error pointer.

A driver using this API must set driver_managed_dma and must not touch the device until this routine succeeds and establishes ownership.

Binding a PCI device places the entire RID under iommufd control.

The caller must undo this with iommufd_device_unbind()

bool iommufd_ctx_has_group(struct iommufd_ctx *ictx, struct iommu_group *group)¶: True if any device within the group is bound to the ictx

Parameters

struct iommufd_ctx *ictx: iommufd file descriptor
struct iommu_group *group: Pointer to a physical iommu_group struct

Description

True if any device within the group has been bound to this ictx, ex. via iommufd_device_bind(), therefore implying ictx ownership of the group.

void iommufd_device_unbind(struct iommufd_device *idev)¶: Undo iommufd_device_bind()

Parameters

struct iommufd_device *idev: Device returned by iommufd_device_bind()

Description

Release the device from iommufd control. The DMA ownership will return back to unowned with DMA controlled by the DMA API. This invalidates the iommufd_device pointer, other APIs that consume it must not be called concurrently.

int iommufd_device_attach(struct iommufd_device *idev, u32 *pt_id)¶: Connect a device to an iommu_domain

Parameters

struct iommufd_device *idev: device to attach
u32 *pt_id: Input a IOMMUFD_OBJ_IOAS, or IOMMUFD_OBJ_HWPT_PAGING Output the IOMMUFD_OBJ_HWPT_PAGING ID

Description

This connects the device to an iommu_domain, either automatically or manually selected. Once this completes the device could do DMA.

The caller should return the resulting pt_id back to userspace. This function is undone by calling iommufd_device_detach().

int iommufd_device_replace(struct iommufd_device *idev, u32 *pt_id)¶: Change the device’s iommu_domain

Parameters

struct iommufd_device *idev: device to change
u32 *pt_id: Input a IOMMUFD_OBJ_IOAS, or IOMMUFD_OBJ_HWPT_PAGING Output the IOMMUFD_OBJ_HWPT_PAGING ID

Description

This is the same as:

iommufd_device_detach();
iommufd_device_attach();

If it fails then no change is made to the attachment. The iommu driver may implement this so there is no disruption in translation. This can only be called if iommufd_device_attach() has already succeeded.

void iommufd_device_detach(struct iommufd_device *idev)¶: Disconnect a device to an iommu_domain

Parameters

struct iommufd_device *idev: device to detach

Description

Undo iommufd_device_attach(). This disconnects the idev from the previously attached pt_id. The device returns back to a blocked DMA translation.

struct iommufd_access *iommufd_access_create(struct iommufd_ctx *ictx, const struct iommufd_access_ops *ops, void *data, u32 *id)¶: Create an iommufd_access

Parameters

struct iommufd_ctx *ictx: iommufd file descriptor
const struct iommufd_access_ops *ops: Driver’s ops to associate with the access
void *data: Opaque data to pass into ops functions
u32 *id: Output ID number to return to userspace for this access

Description

An iommufd_access allows a driver to read/write to the IOAS without using DMA. The underlying CPU memory can be accessed using the iommufd_access_pin_pages() or iommufd_access_rw() functions.

The provided ops are required to use iommufd_access_pin_pages().

void iommufd_access_destroy(struct iommufd_access *access)¶: Destroy an iommufd_access

Parameters

struct iommufd_access *access: The access to destroy

Description

The caller must stop using the access before destroying it.

void iommufd_access_unpin_pages(struct iommufd_access *access, unsigned long iova, unsigned long length)¶: Undo iommufd_access_pin_pages

Parameters

struct iommufd_access *access: IOAS access to act on
unsigned long iova: Starting IOVA
unsigned long length: Number of bytes to access

Description

Return the struct page’s. The caller must stop accessing them before calling this. The iova/length must exactly match the one provided to access_pages.

int iommufd_access_pin_pages(struct iommufd_access *access, unsigned long iova, unsigned long length, struct page **out_pages, unsigned int flags)¶: Return a list of pages under the iova

Parameters

struct iommufd_access *access: IOAS access to act on
unsigned long iova: Starting IOVA
unsigned long length: Number of bytes to access
struct page **out_pages: Output page list
unsigned int flags: IOPMMUFD_ACCESS_RW_* flags

Description

Reads length bytes starting at iova and returns the struct page * pointers. These can be kmap’d by the caller for CPU access.

The caller must perform iommufd_access_unpin_pages() when done to balance this.

This API always requires a page aligned iova. This happens naturally if the ioas alignment is >= PAGE_SIZE and the iova is PAGE_SIZE aligned. However smaller alignments have corner cases where this API can fail on otherwise aligned iova.

int iommufd_access_rw(struct iommufd_access *access, unsigned long iova, void *data, size_t length, unsigned int flags)¶: Read or write data under the iova

Parameters

struct iommufd_access *access: IOAS access to act on
unsigned long iova: Starting IOVA
void *data: Kernel buffer to copy to/from
size_t length: Number of bytes to access
unsigned int flags: IOMMUFD_ACCESS_RW_* flags

Description

Copy kernel to/from data into the range given by IOVA/length. If flags indicates IOMMUFD_ACCESS_RW_KTHREAD then a large copy can be optimized by changing it into copy_to/from_user().

void iommufd_ctx_get(struct iommufd_ctx *ictx)¶: Get a context reference

Parameters

struct iommufd_ctx *ictx: Context to get

Description

The caller must already hold a valid reference to ictx.

struct iommufd_ctx *iommufd_ctx_from_file(struct file *file)¶: Acquires a reference to the iommufd context

Parameters

struct file *file: File to obtain the reference from

Description

Returns a pointer to the iommufd_ctx, otherwise ERR_PTR. The struct file remains owned by the caller and the caller must still do fput. On success the caller is responsible to call iommufd_ctx_put().

struct iommufd_ctx *iommufd_ctx_from_fd(int fd)¶: Acquires a reference to the iommufd context

Parameters

int fd: File descriptor to obtain the reference from

Description

Returns a pointer to the iommufd_ctx, otherwise ERR_PTR. On success the caller is responsible to call iommufd_ctx_put().

void iommufd_ctx_put(struct iommufd_ctx *ictx)¶: Put back a reference

Parameters

struct iommufd_ctx *ictx: Context to put back

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

The Linux Kernel

Contents

This Page

IOMMUFD¶

Overview¶

Key Concepts¶

User Visible Objects¶

Kernel Datastructure¶

IOMMUFD User API¶

IOMMUFD Kernel API¶

VFIO and IOMMUFD¶

Future TODOs¶