This patch introduces the vfio-user protocol specification (formerly known as VFIO-over-socket), which is designed to allow devices to be emulated outside QEMU, in a separate process. vfio-user reuses the existing VFIO defines, structs and concepts.
It has been earlier discussed as an RFC in: "RFC: use VFIO over a UNIX domain socket to implement device offloading" Signed-off-by: John G Johnson <john.g.john...@oracle.com> Signed-off-by: Thanos Makatos <thanos.maka...@nutanix.com> --- Changed since v1: * fix coding style issues * update MAINTAINERS for VFIO-over-socket * add vfio-over-socket to ToC Changed since v2: * fix whitespace Changed since v3: * rename protocol to vfio-user * add table of contents * fix Unicode problems * fix typos and various reStructuredText issues * various stylistic improvements * add backend program conventions * rewrite part of intro, drop QEMU-specific stuff * drop QEMU-specific paragraph about implementation * explain that passing of FDs isn't necessary * minor improvements in the VFIO section * various text substitutions for the sake of consistency * drop paragraph about client and server, already explained in intro * drop device ID * drop type from version * elaborate on request concurrency * convert some inessential paragraphs into notes * explain why some existing VFIO defines cannot be reused * explain how to make changes to the protocol * improve text of DMA map * reword comment about existing VFIO commands * add reference to Version section * reset device on disconnection * reword live migration section * replace sys/vfio.h with linux/vfio.h * drop reference to iovec * use argz the same way it is used in VFIO * add type field in header for clarity Changed since v4: * introduce support for live migration as defined in include/uapi/linux/vfio.h * introduce 'max_fds' and 'migration' capabilities: * remove 'index' from VFIO_USER_DEVICE_GET_IRQ_INFO * fix minor typos and reworded some text for clarity You can focus on v4 to v5 changes by cloning my fork (https://github.com/tmakatos/qemu) and doing: git diff refs/tags/vfio-user/v4 refs/heads/vfio-user/v5 --- MAINTAINERS | 6 + docs/devel/index.rst | 1 + docs/devel/vfio-user.rst | 1552 ++++++++++++++++++++++++++++++++++++++++++++++ 3 files changed, 1559 insertions(+) create mode 100644 docs/devel/vfio-user.rst diff --git a/MAINTAINERS b/MAINTAINERS index 7e442b5247..3611f9e365 100644 --- a/MAINTAINERS +++ b/MAINTAINERS @@ -1754,6 +1754,12 @@ F: hw/vfio/ap.c F: docs/system/s390x/vfio-ap.rst L: qemu-s3...@nongnu.org +vfio-user +M: John G Johnson <john.g.john...@oracle.com> +M: Thanos Makatos <thanos.maka...@nutanix.com> +S: Supported +F: docs/devel/vfio-user.rst + vhost M: Michael S. Tsirkin <m...@redhat.com> S: Supported diff --git a/docs/devel/index.rst b/docs/devel/index.rst index 77baae5c77..7c7740a096 100644 --- a/docs/devel/index.rst +++ b/docs/devel/index.rst @@ -34,3 +34,4 @@ Contents: clocks qom block-coroutine-wrapper + vfio-user diff --git a/docs/devel/vfio-user.rst b/docs/devel/vfio-user.rst new file mode 100644 index 0000000000..d8664e864f --- /dev/null +++ b/docs/devel/vfio-user.rst @@ -0,0 +1,1552 @@ +.. include:: <isonum.txt> + +******************************** +vfio-user Protocol Specification +******************************** + +------------ +Version_ 0.1 +------------ + +.. contents:: Table of Contents + +Introduction +============ +vfio-user is a protocol that allows a device to be emulated in a separate +process outside of a Virtual Machine Monitor (VMM). vfio-user devices consist +of a generic VFIO device type, living inside the VMM, which we call the client, +and the core device implementation, living outside the VMM, which we call the +server. + +The `Linux VFIO ioctl interface <https://www.kernel.org/doc/html/latest/driver-api/vfio.html>`_ +been chosen as the base for this protocol for the following reasons: + +1) It is a mature and stable API, backed by an extensively used framework. +2) The existing VFIO client implementation in QEMU (qemu/hw/vfio/) can be + largely reused. + +.. Note:: + In a proof of concept implementation it has been demonstrated that using VFIO + over a UNIX domain socket is a viable option. vfio-user is designed with + QEMU in mind, however it could be used by other client applications. The + vfio-user protocol does not require that QEMU's VFIO client implementation + is used in QEMU. + +None of the VFIO kernel modules are required for supporting the protocol, +neither in the client nor the server, only the source header files are used. + +The main idea is to allow a virtual device to function in a separate process in +the same host over a UNIX domain socket. A UNIX domain socket (AF_UNIX) is +chosen because file descriptors can be trivially sent over it, which in turn +allows: + +* Sharing of client memory for DMA with the server. +* Sharing of server memory with the client for fast MMIO. +* Efficient sharing of eventfd's for triggering interrupts. + +Other socket types could be used which allow the server to run in a separate +guest in the same host (AF_VSOCK) or remotely (AF_INET). Theoretically the +underlying transport does not necessarily have to be a socket, however we do +not examine such alternatives. In this protocol version we focus on using a +UNIX domain socket and introduce basic support for the other two types of +sockets without considering performance implications. + +While passing of file descriptors is desirable for performance reasons, it is +not necessary neither for the client nor for the server to support it in order +to implement the protocol. There is always an in-band, message-passing fall +back mechanism. + +VFIO +==== +VFIO is a framework that allows a physical device to be securely passed through +to a user space process; the device-specific kernel driver does not drive the +device at all. Typically, the user space process is a VMM and the device is +passed through to it in order to achieve high performance. VFIO provides an API +and the required functionality in the kernel. QEMU has adopted VFIO to allow a +guest to directly access physical devices, instead of emulating them in +software. + +vfio-user reuses the core VFIO concepts defined in its API, but implements them +as messages to be sent over a socket. It does not change the kernel-based VFIO +in any way, in fact none of the VFIO kernel modules need to be loaded to use +vfio-user. It is also possible for the client to concurrently use the current +kernel-based VFIO for one device, and vfio-user for another device. + +VFIO Device Model +----------------- +A device under VFIO presents a standard interface to the user process. Many of +the VFIO operations in the existing interface use the ioctl() system call, and +references to the existing interface are called the ioctl() implementation in +this document. + +The following sections describe the set of messages that implement the VFIO +interface over a socket. In many cases, the messages are direct translations of +data structures used in the ioctl() implementation. Messages derived from +ioctl()s will have a name derived from the ioctl() command name. E.g., the +VFIO_GET_INFO ioctl() command becomes a VFIO_USER_GET_INFO message. The +purpose of this reuse is to share as much code as feasible with the ioctl() +implementation. + +Connection Initiation +^^^^^^^^^^^^^^^^^^^^^ +After the client connects to the server, the initial server message is +VFIO_USER_VERSION to propose a protocol version and set of capabilities to +apply to the session. The client replies with a compatible version and set of +capabilities it supports, or closes the connection if it cannot support the +advertised version. + +DMA Memory Configuration +^^^^^^^^^^^^^^^^^^^^^^^^ +The client uses VFIO_USER_DMA_MAP and VFIO_USER_DMA_UNMAP messages to inform +the server of the valid DMA ranges that the server can access on behalf +of a device. DMA memory may be accessed by the server via VFIO_USER_DMA_READ +and VFIO_USER_DMA_WRITE messages over the socket. + +An optimization for server access to client memory is for the client to provide +file descriptors the server can mmap() to directly access client memory. Note +that mmap() privileges cannot be revoked by the client, therefore file +descriptors should only be exported in environments where the client trusts the +server not to corrupt guest memory. + +Device Information +^^^^^^^^^^^^^^^^^^ +The client uses a VFIO_USER_DEVICE_GET_INFO message to query the server for +information about the device. This information includes: + +* The device type and whether it supports reset (``VFIO_DEVICE_FLAGS_``), +* the number of device regions, and +* the device presents to the client the number of interrupt types the device + supports. + +Region Information +^^^^^^^^^^^^^^^^^^ +The client uses VFIO_USER_DEVICE_GET_REGION_INFO messages to query the server +for information about the device's memory regions. This information describes: + +* Read and write permissions, whether it can be memory mapped, and whether it + supports additional capabilities (``VFIO_REGION_INFO_CAP_``). +* Region index, size, and offset. + +When a region can be mapped by the client, the server provides a file +descriptor which the client can mmap(). The server is responsible for polling +for client updates to memory mapped regions. + +Region Capabilities +""""""""""""""""""" +Some regions have additional capabilities that cannot be described adequately +by the region info data structure. These capabilities are returned in the +region info reply in a list similar to PCI capabilities in a PCI device's +configuration space. + +Sparse Regions +"""""""""""""" +A region can be memory-mappable in whole or in part. When only a subset of a +region can be mapped by the client, a VFIO_REGION_INFO_CAP_SPARSE_MMAP +capability is included in the region info reply. This capability describes +which portions can be mapped by the client. + +.. Note:: + For example, in a virtual NVMe controller, sparse regions can be used so + that accesses to the NVMe registers (found in the beginning of BAR0) are + trapped (an infrequent event), while allowing direct access to the doorbells + (an extremely frequent event as every I/O submission requires a write to + BAR0), found right after the NVMe registers in BAR0. + +Device-Specific Regions +""""""""""""""""""""""" + +A device can define regions additional to the standard ones (e.g. PCI indexes +0-8). This is achieved by including a VFIO_REGION_INFO_CAP_TYPE capability +in the region info reply of a device-specific region. Such regions are reflected +in ``struct vfio_device_info.num_regions``. Thus, for PCI devices this value can +be equal to, or higher than, VFIO_PCI_NUM_REGIONS. + +Interrupts +^^^^^^^^^^ +The client uses VFIO_USER_DEVICE_GET_IRQ_INFO messages to query the server for +the device's interrupt types. The interrupt types are specific to the bus the +device is attached to, and the client is expected to know the capabilities of +each interrupt type. The server can signal an interrupt either with +VFIO_USER_VM_INTERRUPT messages over the socket, or can directly inject +interrupts into the guest via an event file descriptor. The client configures +how the server signals an interrupt with VFIO_USER_SET_IRQS messages. + +Device Read and Write +^^^^^^^^^^^^^^^^^^^^^ +When the guest executes load or store operations to device memory, the client +forwards these operations to the server with VFIO_USER_REGION_READ or +VFIO_USER_REGION_WRITE messages. The server will reply with data from the +device on read operations or an acknowledgement on write operations. + +DMA +^^^ +When a device performs DMA accesses to guest memory, the server will forward +them to the client with VFIO_USER_DMA_READ and VFIO_USER_DMA_WRITE messages. +These messages can only be used to access guest memory the client has +configured into the server. + +Protocol Specification +====================== +To distinguish from the base VFIO symbols, all vfio-user symbols are prefixed +with vfio_user or VFIO_USER. In revision 0.1, all data is in the little-endian +format, although this may be relaxed in future revision in cases where the +client and server are both big-endian. The messages are formatted for seamless +reuse of the native VFIO structs. + +Socket +------ + +A server can serve: + +1) one or more clients, and/or +2) one or more virtual devices, belonging to one or more clients. + +The current protocol specification requires a dedicated socket per +client/server connection. It is a server-side implementation detail whether a +single server handles multiple virtual devices from the same or multiple +clients. The location of the socket is implementation-specific. Multiplexing +clients, devices, and servers over the same socket is not supported in this +version of the protocol. + +Authentication +-------------- +For AF_UNIX, we rely on OS mandatory access controls on the socket files, +therefore it is up to the management layer to set up the socket as required. +Socket types than span guests or hosts will require a proper authentication +mechanism. Defining that mechanism is deferred to a future version of the +protocol. + +Command Concurrency +------------------- +A client may pipeline multiple commands without waiting for previous command +replies. The server will process commands in the order they are received. +A consequence of this is if a client issues a command with the *No_reply* bit, +then subseqently issues a command without *No_reply*, the older command will +have been processed before the reply to the younger command is sent by the +server. The client must be aware of the device's capability to process concurrent +commands if pipelining is used. For example, pipelining allows multiple client +threads to concurently access device memory; the client must ensure these acceses +obey device semantics. + +An example is a frame buffer device, where the device may allow concurrent access +to different areas of video memory, but may have indeterminate behavior if concurrent +acceses are performed to command or status registers. + +Socket Disconnection Behavior +----------------------------- +The server and the client can disconnect from each other, either intentionally +or unexpectedly. Both the client and the server need to know how to handle such +events. + +Server Disconnection +^^^^^^^^^^^^^^^^^^^^ +A server disconnecting from the client may indicate that: + +1) A virtual device has been restarted, either intentionally (e.g. because of a + device update) or unintentionally (e.g. because of a crash). +2) A virtual device has been shut down with no intention to be restarted. + +It is impossible for the client to know whether or not a failure is +intermittent or innocuous and should be retried, therefore the client should +reset the VFIO device when it detects the socket has been disconnected. +Error recovery will be driven by the guest's device error handling +behavior. + +Client Disconnection +^^^^^^^^^^^^^^^^^^^^ +The client disconnecting from the server primarily means that the client +has exited. Currently, this means that the guest is shut down so the device is +no longer needed therefore the server can automatically exit. However, there +can be cases where a client disconnection should not result in a server exit: + +1) A single server serving multiple clients. +2) A multi-process QEMU upgrading itself step by step, which is not yet + implemented. + +Therefore in order for the protocol to be forward compatible the server should +take no action when the client disconnects. If anything happens to the client +the control stack will know about it and can clean up resources +accordingly. + +Request Retry and Response Timeout +^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ +A failed command is a command that has been successfully sent and has been +responded to with an error code. Failure to send the command in the first place +(e.g. because the socket is disconnected) is a different type of error examined +earlier in the disconnect section. + +.. Note:: + QEMU's VFIO retries certain operations if they fail. While this makes sense + for real HW, we don't know for sure whether it makes sense for virtual + devices. + +Defining a retry and timeout scheme is deferred to a future version of the +protocol. + +.. _Commands: + +Commands +-------- +The following table lists the VFIO message command IDs, and whether the +message command is sent from the client or the server. + ++----------------------------------+---------+-------------------+ +| Name | Command | Request Direction | ++==================================+=========+===================+ +| VFIO_USER_VERSION | 1 | server -> client | ++----------------------------------+---------+-------------------+ +| VFIO_USER_DMA_MAP | 2 | client -> server | ++----------------------------------+---------+-------------------+ +| VFIO_USER_DMA_UNMAP | 3 | client -> server | ++----------------------------------+---------+-------------------+ +| VFIO_USER_DEVICE_GET_INFO | 4 | client -> server | ++----------------------------------+---------+-------------------+ +| VFIO_USER_DEVICE_GET_REGION_INFO | 5 | client -> server | ++----------------------------------+---------+-------------------+ +| VFIO_USER_DEVICE_GET_IRQ_INFO | 6 | client -> server | ++----------------------------------+---------+-------------------+ +| VFIO_USER_DEVICE_SET_IRQS | 7 | client -> server | ++----------------------------------+---------+-------------------+ +| VFIO_USER_REGION_READ | 8 | client -> server | ++----------------------------------+---------+-------------------+ +| VFIO_USER_REGION_WRITE | 9 | client -> server | ++----------------------------------+---------+-------------------+ +| VFIO_USER_DMA_READ | 10 | server -> client | ++----------------------------------+---------+-------------------+ +| VFIO_USER_DMA_WRITE | 11 | server -> client | ++----------------------------------+---------+-------------------+ +| VFIO_USER_VM_INTERRUPT | 12 | server -> client | ++----------------------------------+---------+-------------------+ +| VFIO_USER_DEVICE_RESET | 13 | client -> server | ++----------------------------------+---------+-------------------+ +| VFIO_USER_DIRTY_PAGES | 14 | client -> server | ++----------------------------------+---------+-------------------+ + + +.. Note:: Some VFIO defines cannot be reused since their values are + architecture-specific (e.g. VFIO_IOMMU_MAP_DMA). + +Header +------ +All messages, both command messages and reply messages, are preceded by a +header that contains basic information about the message. The header is +followed by message-specific data described in the sections below. + ++----------------+--------+-------------+ +| Name | Offset | Size | ++================+========+=============+ +| Message ID | 0 | 2 | ++----------------+--------+-------------+ +| Command | 2 | 2 | ++----------------+--------+-------------+ +| Message size | 4 | 4 | ++----------------+--------+-------------+ +| Flags | 8 | 4 | ++----------------+--------+-------------+ +| | +-----+------------+ | +| | | Bit | Definition | | +| | +=====+============+ | +| | | 0-3 | Type | | +| | +-----+------------+ | +| | | 4 | No_reply | | +| | +-----+------------+ | +| | | 5 | Error | | +| | +-----+------------+ | ++----------------+--------+-------------+ +| Error | 12 | 4 | ++----------------+--------+-------------+ +| <message data> | 16 | variable | ++----------------+--------+-------------+ + +* *Message ID* identifies the message, and is echoed in the command's reply message. +* *Command* specifies the command to be executed, listed in Commands_. +* *Message size* contains the size of the entire message, including the header. +* *Flags* contains attributes of the message: + + * The *Type* bits indicate the message type. + + * *Command* (value 0x0) indicates a command message. + * *Reply* (value 0x1) indicates a reply message acknowledging a previous + command with the same message ID. + * *No_reply* in a command message indicates that no reply is needed for this command. + This is commonly used when multiple commands are sent, and only the last needs + acknowledgement. + * *Error* in a reply message indicates the command being acknowledged had + an error. In this case, the *Error* field will be valid. + +* *Error* in a reply message is a UNIX errno value. It is reserved in a command message. + +Each command message in Commands_ must be replied to with a reply message, unless the +message sets the *No_Reply* bit. The reply consists of the header with the *Reply* +bit set, plus any additional data. + +VFIO_USER_VERSION +----------------- + +Message format +^^^^^^^^^^^^^^ + ++--------------+------------------------+ +| Name | Value | ++==============+========================+ +| Message ID | <ID> | ++--------------+------------------------+ +| Command | 1 | ++--------------+------------------------+ +| Message size | 16 + version length | ++--------------+------------------------+ +| Flags | Reply bit set in reply | ++--------------+------------------------+ +| Error | 0/errno | ++--------------+------------------------+ +| Version | JSON byte array | ++--------------+------------------------+ + +This is the initial message sent by the server after the socket connection is +established. The version is in JSON format, and the following objects must be +included: + ++--------------+--------+---------------------------------------------------+ +| Name | Type | Description | ++==============+========+===================================================+ +| version | object | ``{"major": <number>, "minor": <number>}`` | +| | | | +| | | Version supported by the sender, e.g. "0.1". | ++--------------+--------+---------------------------------------------------+ +| capabilities | array | Reserved. Can be omitted for v0.1, otherwise must | +| | | be empty. | ++--------------+--------+---------------------------------------------------+ + +Common capabilities: + ++---------------+------------------------------------------------------------+ +| Name | Description | ++===============+============================================================+ +| ``max_fds`` | Maximum number of file descriptors that can be received by | +| | the sender. Optional. | ++---------------+------------------------------------------------------------+ +| ``migration`` | Migration capability object with the following format: | +| | | +| | +------------+-------------------------------------------+ | +| | | Name | Description | | +| | +============+===========================================+ | +| | | ``pgsize`` | Page size of dirty pages bitmap. The | | +| | | | smallest between the client and the | | +| | | | server is used. | | +| | +------------+-------------------------------------------+ | ++---------------+------------------------------------------------------------+ + +.. _Version: + +Versioning and Feature Support +^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ +Upon accepting a connection, the server must send a VFIO_USER_VERSION message +proposing a protocol version and a set of capabilities. The client compares +these with the versions and capabilities it supports and sends a +VFIO_USER_VERSION reply according to the following rules. + +* The major version in the reply must be the same as proposed. If the client + does not support the proposed major, it closes the connection. +* The minor version in the reply must be equal to or less than the minor + version proposed. +* The capability list must be a subset of those proposed. If the client + requires a capability the server did not include, it closes the connection. + +The protocol major version will only change when incompatible protocol changes +are made, such as changing the message format. The minor version may change +when compatible changes are made, such as adding new messages or capabilities, +Both the client and server must support all minor versions less than the +maximum minor version it supports. E.g., an implementation that supports +version 1.3 must also support 1.0 through 1.2. + +When making a change to this specification, the protocol version number must +be included in the form "added in version X.Y" + + +VFIO_USER_DMA_MAP and VFIO_USER_DMA_UNMAP +----------------------------------------- + +Message Format +^^^^^^^^^^^^^^ + ++--------------+------------------------+ +| Name | Value | ++==============+========================+ +| Message ID | <ID> | ++--------------+------------------------+ +| Command | MAP=2, UNMAP=3 | ++--------------+------------------------+ +| Message size | 16 + table size | ++--------------+------------------------+ +| Flags | Reply bit set in reply | ++--------------+------------------------+ +| Error | 0/errno | ++--------------+------------------------+ +| Table | array of table entries | ++--------------+------------------------+ + +This command message is sent by the client to the server to inform it of the +memory regions the server can access. It must be sent before the server can +perform any DMA to the client. It is normally sent directly after the version +handshake is completed, but may also occur when memory is added to or +subtracted from the client, or if the client uses a vIOMMU. If the client does +not expect the server to perform DMA then it does not need to send to the +server VFIO_USER_DMA_MAP and VFIO_USER_DMA_UNMAP commands. If the server does +not need to perform DMA then it can ignore such commands but it must still +reply to them. The table is an array of the following structure. This +structure is 32 bytes in size, so the message size is: +16 + (# of table entries * 32). + +VFIO bitmap format +^^^^^^^^^^^^^^^^^^^^^^ + ++--------+--------+------+ +| Name | Offset | Size | ++========+========+======+ +| pgsize | 0 | 8 | ++--------+--------+------+ +| size | 8 | 8 | ++--------+--------+------+ +| data | 16 | 8 | ++--------+--------+------+ + +* *pgsize* is the page size for the bitmap, in bytes. +* *size* the size for the bitmap, in bytes. +* *data* This field is unused in vfio-user. + +The VFIO bitmap structure is defined in ``<linux/vfio.h>`` +(``struct vfio_bitmap``). + +Table entry format +^^^^^^^^^^^^^^^^^^ + ++-------------+--------+--------------------------------------------------+ +| Name | Offset | Size | ++=============+========+==================================================+ +| Address | 0 | 8 | ++-------------+--------+--------------------------------------------------+ +| Size | 8 | 8 | ++-------------+--------+--------------------------------------------------+ +| Offset | 16 | 8 | ++-------------+--------+--------------------------------------------------+ +| Protections | 24 | 4 | ++-------------+--------+--------------------------------------------------+ +| Flags | 28 | 4 | ++-------------+--------+--------------------------------------------------+ +| | +-----+-------------------------------------------------+ | +| | | Bit | Definition | | +| | +=====+=================================================+ | +| | | 0 | Mappable/VFIO_DMA_UNMAP_FLAG_GET_DIRTY_BITMAP | | +| | +-----+-------------------------------------------------+ | ++-------------+--------+--------------------------------------------------+ +| Data | 32 | variable | ++-------------+--------+--------------------------------------------------+ + + +* *Address* is the base DMA address of the region. +* *Size* is the size of the region. +* *Offset* is the file offset of the region with respect to the associated file + descriptor. +* *Protections* are the region's protection attributes as encoded in + ``<sys/mman.h>``. +* *Flags* contain the following region attributes: + + * *Mappable* indicates that the region can be mapped via the mmap() system call + using the file descriptor provided in the message meta-data. This flag is + only valid for VFIO_USER_DMA_MAP. + + * *VFIO_DMA_UNMAP_FLAG_GET_DIRTY_BITMAP* indicates that a dirty page bitmap + must be populated before unmapping the the DMA region. This flag is only + valid for VFIO_USER_DMA_UNMAP. The client must provide a + ``struct vfio_bitmap`` in the data field with the ``vfio_bitmap.pgsize`` + and ``vfio_bitmap.size`` fields initialized. + +VFIO_USER_DMA_MAP +""""""""""""""""" +If a DMA region being added can be directly mapped by the server, an array of +file descriptors must be sent as part of the message meta-data. Each region +entry must have a corresponding file descriptor. On AF_UNIX sockets, the file +descriptors must be passed as SCM_RIGHTS type ancillary data. Otherwise, if a +DMA region cannot be directly mapped by the server, it can be accessed by the +server using VFIO_USER_DMA_READ and VFIO_USER_DMA_WRITE messages, explained in +`Read and Write Operations`_. A command to map over an existing region must be +failed by the server with ``EEXIST`` set in error field in the reply. + +VFIO_USER_DMA_UNMAP +""""""""""""""""""" +Upon receiving a VFIO_USER_DMA_UNMAP command, if the file descriptor is mapped +then the server must release all references to that DMA region before replying, +which includes potentially in flight DMA transactions. Removing a portion of a +DMA region is possible. If the VFIO_DMA_UNMAP_FLAG_GET_DIRTY_BITMAP bit is set +in the request, the server must append to the header the ``struct vfio_bitmap`` +received in the command, followed by the bitmap. Thus, the message size the +client should is expect is the size of the header plus the size of +``struct vfio_bitmap`` plus ``vfio_bitmap.size`` bytes. Each bit in the bitmap +represents one page of size ``vfio_bitmap.pgsize``. + +.. Note:: + I suppose dirt page logging must have been previously enabled in order for the + client to be able to use the VFIO_DMA_UNMAP_FLAG_GET_DIRTY_BITMAP flag? + +VFIO_USER_DEVICE_GET_INFO +------------------------- + +Message format +^^^^^^^^^^^^^^ + ++--------------+----------------------------+ +| Name | Value | ++==============+============================+ +| Message ID | <ID> | ++--------------+----------------------------+ +| Command | 4 | ++--------------+----------------------------+ +| Message size | 16 in command, 32 in reply | ++--------------+----------------------------+ +| Flags | Reply bit set in reply | ++--------------+----------------------------+ +| Error | 0/errno | ++--------------+----------------------------+ +| Device info | VFIO device info | ++--------------+----------------------------+ + +This command message is sent by the client to the server to query for basic +information about the device. Only the message header is needed in the command +message. The VFIO device info structure is defined in ``<linux/vfio.h>`` +(``struct vfio_device_info``). + +VFIO device info format +^^^^^^^^^^^^^^^^^^^^^^^ + ++-------------+--------+--------------------------+ +| Name | Offset | Size | ++=============+========+==========================+ +| argsz | 16 | 4 | ++-------------+--------+--------------------------+ +| flags | 20 | 4 | ++-------------+--------+--------------------------+ +| | +-----+-------------------------+ | +| | | Bit | Definition | | +| | +=====+=========================+ | +| | | 0 | VFIO_DEVICE_FLAGS_RESET | | +| | +-----+-------------------------+ | +| | | 1 | VFIO_DEVICE_FLAGS_PCI | | +| | +-----+-------------------------+ | ++-------------+--------+--------------------------+ +| num_regions | 24 | 4 | ++-------------+--------+--------------------------+ +| num_irqs | 28 | 4 | ++-------------+--------+--------------------------+ + +* *argsz* is the size of the VFIO device info structure. +* *flags* contains the following device attributes. + + * VFIO_DEVICE_FLAGS_RESET indicates that the device supports the + VFIO_USER_DEVICE_RESET message. + * VFIO_DEVICE_FLAGS_PCI indicates that the device is a PCI device. + +* *num_regions* is the number of memory regions that the device exposes. +* *num_irqs* is the number of distinct interrupt types that the device supports. + +This version of the protocol only supports PCI devices. Additional devices may +be supported in future versions. + +VFIO_USER_DEVICE_GET_REGION_INFO +-------------------------------- + +Message format +^^^^^^^^^^^^^^ + ++--------------+------------------------+ +| Name | Value | ++==============+========================+ +| Message ID | <ID> | ++--------------+------------------------+ +| Command | 5 | ++--------------+------------------------+ +| Message size | 48 + any caps | ++--------------+------------------------+ +| Flags | Reply bit set in reply | ++--------------+------------------------+ +| Error | 0/errno | ++--------------+------------------------+ +| Region info | VFIO region info | ++--------------+------------------------+ + +This command message is sent by the client to the server to query for +information about device memory regions. The VFIO region info structure is +defined in ``<linux/vfio.h>`` (``struct vfio_region_info``). Since the client +does not know the size of the capabilities, the size of the reply it should +expect is 48 plus any capabilities whose size is indicated in the size field of +the reply header. + +VFIO region info format +^^^^^^^^^^^^^^^^^^^^^^^ + ++------------+--------+------------------------------+ +| Name | Offset | Size | ++============+========+==============================+ +| argsz | 16 | 4 | ++------------+--------+------------------------------+ +| flags | 20 | 4 | ++------------+--------+------------------------------+ +| | +-----+-----------------------------+ | +| | | Bit | Definition | | +| | +=====+=============================+ | +| | | 0 | VFIO_REGION_INFO_FLAG_READ | | +| | +-----+-----------------------------+ | +| | | 1 | VFIO_REGION_INFO_FLAG_WRITE | | +| | +-----+-----------------------------+ | +| | | 2 | VFIO_REGION_INFO_FLAG_MMAP | | +| | +-----+-----------------------------+ | +| | | 3 | VFIO_REGION_INFO_FLAG_CAPS | | +| | +-----+-----------------------------+ | ++------------+--------+------------------------------+ +| index | 24 | 4 | ++------------+--------+------------------------------+ +| cap_offset | 28 | 4 | ++------------+--------+------------------------------+ +| size | 32 | 8 | ++------------+--------+------------------------------+ +| offset | 40 | 8 | ++------------+--------+------------------------------+ + +* *argsz* is the size of the VFIO region info structure plus the + size of any region capabilities returned. +* *flags* are attributes of the region: + + * *VFIO_REGION_INFO_FLAG_READ* allows client read access to the region. + * *VFIO_REGION_INFO_FLAG_WRITE* allows client write access to the region. + * *VFIO_REGION_INFO_FLAG_MMAP* specifies the client can mmap() the region. + When this flag is set, the reply will include a file descriptor in its + meta-data. On AF_UNIX sockets, the file descriptors will be passed as + SCM_RIGHTS type ancillary data. + * *VFIO_REGION_INFO_FLAG_CAPS* indicates additional capabilities found in the + reply. + +* *index* is the index of memory region being queried, it is the only field + that is required to be set in the command message. +* *cap_offset* describes where additional region capabilities can be found. + cap_offset is relative to the beginning of the VFIO region info structure. + The data structure it points is a VFIO cap header defined in + ``<linux/vfio.h>``. +* *size* is the size of the region. +* *offset* is the offset given to the mmap() system call for regions with the + MMAP attribute. It is also used as the base offset when mapping a VFIO + sparse mmap area, described below. + +VFIO Region capabilities +^^^^^^^^^^^^^^^^^^^^^^^^ +The VFIO region information can also include a capabilities list. This list is +similar to a PCI capability list - each entry has a common header that +identifies a capability and where the next capability in the list can be found. +The VFIO capability header format is defined in ``<linux/vfio.h>`` (``struct +vfio_info_cap_header``). + +VFIO cap header format +^^^^^^^^^^^^^^^^^^^^^^ + ++---------+--------+------+ +| Name | Offset | Size | ++=========+========+======+ +| id | 0 | 2 | ++---------+--------+------+ +| version | 2 | 2 | ++---------+--------+------+ +| next | 4 | 4 | ++---------+--------+------+ + +* *id* is the capability identity. +* *version* is a capability-specific version number. +* *next* specifies the offset of the next capability in the capability list. It + is relative to the beginning of the VFIO region info structure. + +VFIO sparse mmap +^^^^^^^^^^^^^^^^ + ++------------------+----------------------------------+ +| Name | Value | ++==================+==================================+ +| id | VFIO_REGION_INFO_CAP_SPARSE_MMAP | ++------------------+----------------------------------+ +| version | 0x1 | ++------------------+----------------------------------+ +| next | <next> | ++------------------+----------------------------------+ +| sparse mmap info | VFIO region info sparse mmap | ++------------------+----------------------------------+ + +This capability is defined when only a subrange of the region supports +direct access by the client via mmap(). The VFIO sparse mmap area is defined in +``<linux/vfio.h>`` (``struct vfio_region_sparse_mmap_area``). + +VFIO region info cap sparse mmap +^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ ++----------+--------+------+ +| Name | Offset | Size | ++==========+========+======+ +| nr_areas | 0 | 4 | ++----------+--------+------+ +| reserved | 4 | 4 | ++----------+--------+------+ +| offset | 8 | 8 | ++----------+--------+------+ +| size | 16 | 9 | ++----------+--------+------+ +| ... | | | ++----------+--------+------+ + +* *nr_areas* is the number of sparse mmap areas in the region. +* *offset* and size describe a single area that can be mapped by the client. + There will be nr_areas pairs of offset and size. The offset will be added to + the base offset given in the VFIO_USER_DEVICE_GET_REGION_INFO to form the + offset argument of the subsequent mmap() call. + +The VFIO sparse mmap area is defined in ``<linux/vfio.h>`` (``struct +vfio_region_info_cap_sparse_mmap``). + +VFIO Region Type +^^^^^^^^^^^^^^^^ + ++------------------+---------------------------+ +| Name | Value | ++==================+===========================+ +| id | VFIO_REGION_INFO_CAP_TYPE | ++------------------+---------------------------+ +| version | 0x1 | ++------------------+---------------------------+ +| next | <next> | ++------------------+---------------------------+ +| region info type | VFIO region info type | ++------------------+---------------------------+ + +This capability is defined when a region is specific to the device. + +VFIO region info type +^^^^^^^^^^^^^^^^^^^^^ + +The VFIO region info type is defined in ``<linux/vfio.h>`` +(``struct vfio_region_info_cap_type``). + ++---------+--------+------+ +| Name | Offset | Size | ++=========+========+======+ +| type | 0 | 4 | ++---------+--------+------+ +| subtype | 4 | 4 | ++---------+--------+------+ + +The only device-specific region type and subtype supported by vfio-user is +VFIO_REGION_TYPE_MIGRATION (3) and VFIO_REGION_SUBTYPE_MIGRATION (1). + +VFIO Device Migration Info +^^^^^^^^^^^^^^^^^^^^^^^^^^ + +The beginning of the subregion must contain +``struct vfio_device_migration_info``, defined in ``<linux/vfio.h>``. This +subregion is accessed like any other part of a standard vfio-user PCI region +using VFIO_USER_REGION_READ/VFIO_USER_REGION_WRITE. + ++---------------+--------+-----------------------------+ +| Name | Offset | Size | ++===============+========+=============================+ +| device_state | 0 | 4 | ++---------------+--------+-----------------------------+ +| | +-----+----------------------------+ | +| | | Bit | Definition | | +| | +=====+============================+ | +| | | 0 | VFIO_DEVICE_STATE_RUNNING | | +| | +-----+----------------------------+ | +| | | 1 | VFIO_DEVICE_STATE_SAVING | | +| | +-----+----------------------------+ | +| | | 2 | VFIO_DEVICE_STATE_RESUMING | | +| | +-----+----------------------------+ | ++---------------+--------+-----------------------------+ +| reserved | 4 | 4 | ++---------------+--------+-----------------------------+ +| pending_bytes | 8 | 8 | ++---------------+--------+-----------------------------+ +| data_offset | 16 | 8 | ++---------------+--------+-----------------------------+ +| data_size | 24 | 8 | ++---------------+--------+-----------------------------+ + +* *device_state* defines the state of the device: + + The client initiates device state transition by writing the intended state. + The server must respond only after it has succesfully transitioned to the new + state. If an error occurs then the server must respond to the + VFIO_USER_REGION_WRITE operation with the Error field set accordingly and + must remain at the previous state, or in case of internal error it must + transtition to the error state, defined as + VFIO_DEVICE_STATE_RESUMING | VFIO_DEVICE_STATE_SAVING. The client must + re-read the device state in order to determine it afresh. + + The following device states are defined: + + +-----------+---------+----------+-----------------------------------+ + | _RESUMING | _SAVING | _RUNNING | Description | + +===========+=========+==========+===================================+ + | 0 | 0 | 0 | Device is stopped. | + +-----------+---------+----------+-----------------------------------+ + | 0 | 0 | 1 | Device is running, default state. | + +-----------+---------+----------+-----------------------------------+ + | 0 | 1 | 0 | Stop-and-copy state | + +-----------+---------+----------+-----------------------------------+ + | 0 | 1 | 1 | Pre-copy state | + +-----------+---------+----------+-----------------------------------+ + | 1 | 0 | 0 | Resuming | + +-----------+---------+----------+-----------------------------------+ + | 1 | 0 | 1 | Invalid state | + +-----------+---------+----------+-----------------------------------+ + | 1 | 1 | 1 | Error state | + +-----------+---------+----------+-----------------------------------+ + | 1 | 1 | 1 | Invalid state | + +-----------+---------+----------+-----------------------------------+ + + Valid state transitions are shown in the following table: + + +-------------------------+---------+---------+---------------+----------+----------+ + | |darr| From / To |rarr| | Stopped | Running | Stop-and-copy | Pre-copy | Resuming | + +=========================+=========+=========+===============+==========+==========+ + | Stopped | \- | 0 | 0 | 0 | 0 | + +-------------------------+---------+---------+---------------+----------+----------+ + | Running | 1 | \- | 1 | 1 | 1 | + +-------------------------+---------+---------+---------------+----------+----------+ + | Stop-and-copy | 1 | 0 | \- | 0 | 0 | + +-------------------------+---------+---------+---------------+----------+----------+ + | Pre-copy | 0 | 0 | 1 | \- | 0 | + +-------------------------+---------+---------+---------------+----------+----------+ + | Resuming | 0 | 1 | 0 | 0 | \- | + +-------------------------+---------+---------+---------------+----------+----------+ + + A device is migrated to the destination as follows: + + * The source client transitions the device state from the running state to + the pre-copy state. This transition is optional for the client but must be + supported by the server. The souce server starts sending device state data + to the source client through the migration region while the device is + running. + + * The source client transitions the device state from the running state or the + pre-copy state to the stop-and-copy state. The source server stops the + device, saves device state and sends it to the source client through the + migration region. + + The source client is responsible for sending the migration data to the + destination client. + + A device is resumed on the destination as follows: + + * The destination client transitions the device state from the running state + to the resuming state. The destination server uses the device state data + received through the migration region to resume the device. + + * The destination client provides saved device state to the destination + server and then transitions the device to back to the running state. + +* *reserved* This field is reserved and any access to it must be ignored by the + server. + +* *pending_bytes* Remaining bytes to be migrated by the server. This field is + read only. + +* *data_offset* Offset in the migration region where the client must: + + * read from, during the pre-copy or stop-and-copy state, or + + * write to, during the resuming state. + + This field is read only. + +* *data_size* Contains the size, in bytes, of the amount of data copied to: + + * the source migration region by the source server during the pre-copy or + stop-and copy state, or + + * the destination migration region by the destination client during the + resuming state. + +Device-specific data must be stored at any position after +`struct vfio_device_migration_info`. Note that the migration region can be +memory mappable, even partially. In practise, only the migration data portion +can be memory mapped. + +The client processes device state data during the pre-copy and the +stop-and-copy state in the following iterative manner: + + 1. The client reads `pending_bytes` to mark a new iteration. Repeated reads + of this field is an idempotent operation. If there are no migration data + to be consumed then the next step depends on the current device state: + + * pre-copy: the client must try again. + + * stop-and-copy: this procedure can end and the device can now start + resuming on the destination. + + 2. The client reads `data_offset`; at thich point the server must make + available a portion of migration data at this offset to be read by the + client, which must happen *before* completing the read operation. The + amount of data to be read must be stored in the `data_size` field, which + the client reads next. + + 3. The client reads `data_size` to determine the amount of migration data + available. + + 4. The client reads and processes the migration data. + + 5. Go to step 1. + +Note that the client can transition the device from the pre-copy state to the +stop-and-copy state at any time; `pending_bytes` does not need to become zero. + +The client initializes the device state on the destination by setting the +device state in the resuming state and writing the migration data to the +destination migration region at `data_offset` offset. The client can write the +source migration data in an iterative manner and the server must consume this +data before completing each write operation, updating the `data_offset` field. +The server must apply the source migration data on the device resume state. The +client must write data on the same order and transction size as read. + +If an error occurs then the server must fail the read or write operation. It is +an implementation detail of the client how to handle errors. + +VFIO_USER_DEVICE_GET_IRQ_INFO +----------------------------- + +Message format +^^^^^^^^^^^^^^ + ++--------------+------------------------+ +| Name | Value | ++==============+========================+ +| Message ID | <ID> | ++--------------+------------------------+ +| Command | 6 | ++--------------+------------------------+ +| Message size | 32 | ++--------------+------------------------+ +| Flags | Reply bit set in reply | ++--------------+------------------------+ +| Error | 0/errno | ++--------------+------------------------+ +| IRQ info | VFIO IRQ info | ++--------------+------------------------+ + +This command message is sent by the client to the server to query for +information about device interrupt types. The VFIO IRQ info structure is +defined in ``<linux/vfio.h>`` (``struct vfio_irq_info``). + +VFIO IRQ info format +^^^^^^^^^^^^^^^^^^^^ + ++-------+--------+---------------------------+ +| Name | Offset | Size | ++=======+========+===========================+ +| argsz | 16 | 4 | ++-------+--------+---------------------------+ +| flags | 20 | 4 | ++-------+--------+---------------------------+ +| | +-----+--------------------------+ | +| | | Bit | Definition | | +| | +=====+==========================+ | +| | | 0 | VFIO_IRQ_INFO_EVENTFD | | +| | +-----+--------------------------+ | +| | | 1 | VFIO_IRQ_INFO_MASKABLE | | +| | +-----+--------------------------+ | +| | | 2 | VFIO_IRQ_INFO_AUTOMASKED | | +| | +-----+--------------------------+ | +| | | 3 | VFIO_IRQ_INFO_NORESIZE | | +| | +-----+--------------------------+ | ++-------+--------+---------------------------+ +| index | 24 | 4 | ++-------+--------+---------------------------+ +| count | 28 | 4 | ++-------+--------+---------------------------+ + +* *argsz* is the size of the VFIO IRQ info structure. +* *flags* defines IRQ attributes: + + * *VFIO_IRQ_INFO_EVENTFD* indicates the IRQ type can support server eventfd + signalling. + * *VFIO_IRQ_INFO_MASKABLE* indicates that the IRQ type supports the MASK and + UNMASK actions in a VFIO_USER_DEVICE_SET_IRQS message. + * *VFIO_IRQ_INFO_AUTOMASKED* indicates the IRQ type masks itself after being + triggered, and the client must send an UNMASK action to receive new + interrupts. + * *VFIO_IRQ_INFO_NORESIZE* indicates VFIO_USER_SET_IRQS operations setup + interrupts as a set, and new sub-indexes cannot be enabled without disabling + the entire type. + +* index is the index of IRQ type being queried, it is the only field that is + required to be set in the command message. +* count describes the number of interrupts of the queried type. + +VFIO_USER_DEVICE_SET_IRQS +------------------------- + +Message format +^^^^^^^^^^^^^^ + ++--------------+------------------------+ +| Name | Value | ++==============+========================+ +| Message ID | <ID> | ++--------------+------------------------+ +| Command | 7 | ++--------------+------------------------+ +| Message size | 36 + any data | ++--------------+------------------------+ +| Flags | Reply bit set in reply | ++--------------+------------------------+ +| Error | 0/errno | ++--------------+------------------------+ +| IRQ set | VFIO IRQ set | ++--------------+------------------------+ + +This command message is sent by the client to the server to set actions for +device interrupt types. The VFIO IRQ set structure is defined in +``<linux/vfio.h>`` (``struct vfio_irq_set``). + +VFIO IRQ set format +^^^^^^^^^^^^^^^^^^^ + ++-------+--------+------------------------------+ +| Name | Offset | Size | ++=======+========+==============================+ +| argsz | 16 | 4 | ++-------+--------+------------------------------+ +| flags | 20 | 4 | ++-------+--------+------------------------------+ +| | +-----+-----------------------------+ | +| | | Bit | Definition | | +| | +=====+=============================+ | +| | | 0 | VFIO_IRQ_SET_DATA_NONE | | +| | +-----+-----------------------------+ | +| | | 1 | VFIO_IRQ_SET_DATA_BOOL | | +| | +-----+-----------------------------+ | +| | | 2 | VFIO_IRQ_SET_DATA_EVENTFD | | +| | +-----+-----------------------------+ | +| | | 3 | VFIO_IRQ_SET_ACTION_MASK | | +| | +-----+-----------------------------+ | +| | | 4 | VFIO_IRQ_SET_ACTION_UNMASK | | +| | +-----+-----------------------------+ | +| | | 5 | VFIO_IRQ_SET_ACTION_TRIGGER | | +| | +-----+-----------------------------+ | ++-------+--------+------------------------------+ +| index | 24 | 4 | ++-------+--------+------------------------------+ +| start | 28 | 4 | ++-------+--------+------------------------------+ +| count | 32 | 4 | ++-------+--------+------------------------------+ +| data | 36 | variable | ++-------+--------+------------------------------+ + +* *argsz* is the size of the VFIO IRQ set structure, including any *data* field. +* *flags* defines the action performed on the interrupt range. The DATA flags + describe the data field sent in the message; the ACTION flags describe the + action to be performed. The flags are mutually exclusive for both sets. + + * *VFIO_IRQ_SET_DATA_NONE* indicates there is no data field in the command. + The action is performed unconditionally. + * *VFIO_IRQ_SET_DATA_BOOL* indicates the data field is an array of boolean + bytes. The action is performed if the corresponding boolean is true. + * *VFIO_IRQ_SET_DATA_EVENTFD* indicates an array of event file descriptors + was sent in the message meta-data. These descriptors will be signalled when + the action defined by the action flags occurs. In AF_UNIX sockets, the + descriptors are sent as SCM_RIGHTS type ancillary data. + * *VFIO_IRQ_SET_ACTION_MASK* indicates a masking event. It can be used with + VFIO_IRQ_SET_DATA_BOOL or VFIO_IRQ_SET_DATA_NONE to mask an interrupt, or + with VFIO_IRQ_SET_DATA_EVENTFD to generate an event when the guest masks + the interrupt. + * *VFIO_IRQ_SET_ACTION_UNMASK* indicates an unmasking event. It can be used + with VFIO_IRQ_SET_DATA_BOOL or VFIO_IRQ_SET_DATA_NONE to unmask an + interrupt, or with VFIO_IRQ_SET_DATA_EVENTFD to generate an event when the + guest unmasks the interrupt. + * *VFIO_IRQ_SET_ACTION_TRIGGER* indicates a triggering event. It can be used + with VFIO_IRQ_SET_DATA_BOOL or VFIO_IRQ_SET_DATA_NONE to trigger an + interrupt, or with VFIO_IRQ_SET_DATA_EVENTFD to generate an event when the + server triggers the interrupt. + +* *index* is the index of IRQ type being setup. +* *start* is the start of the sub-index being set. +* *count* describes the number of sub-indexes being set. As a special case, a + count of 0 with data flags of VFIO_IRQ_SET_DATA_NONE disables all interrupts + of the index. +* *data* is an optional field included when the + VFIO_IRQ_SET_DATA_BOOL flag is present. It contains an array of booleans + that specify whether the action is to be performed on the corresponding + index. It's used when the action is only performed on a subset of the range + specified. + +Not all interrupt types support every combination of data and action flags. +The client must know the capabilities of the device and IRQ index before it +sends a VFIO_USER_DEVICE_SET_IRQ message. + +.. _Read and Write Operations: + +Read and Write Operations +------------------------- + +Not all I/O operations between the client and server can be done via direct +access of memory mapped with an mmap() call. In these cases, the client and +server use messages sent over the socket. It is expected that these operations +will have lower performance than direct access. + +The client can access server memory with VFIO_USER_REGION_READ and +VFIO_USER_REGION_WRITE commands. These share a common data structure that +appears after the message header. + +REGION Read/Write Data +^^^^^^^^^^^^^^^^^^^^^^ + ++--------+--------+----------+ +| Name | Offset | Size | ++========+========+==========+ +| Offset | 16 | 8 | ++--------+--------+----------+ +| Region | 24 | 4 | ++--------+--------+----------+ +| Count | 28 | 4 | ++--------+--------+----------+ +| Data | 32 | variable | ++--------+--------+----------+ + +* *Offset* into the region being accessed. +* *Region* is the index of the region being accessed. +* *Count* is the size of the data to be transferred. +* *Data* is the data to be read or written. + +The server can access client memory with VFIO_USER_DMA_READ and +VFIO_USER_DMA_WRITE messages. These also share a common data structure that +appears after the message header. + +DMA Read/Write Data +^^^^^^^^^^^^^^^^^^^ + ++---------+--------+----------+ +| Name | Offset | Size | ++=========+========+==========+ +| Address | 16 | 8 | ++---------+--------+----------+ +| Count | 24 | 4 | ++---------+--------+----------+ +| Data | 28 | variable | ++---------+--------+----------+ + +* *Address* is the area of client memory being accessed. This address must have + been previously exported to the server with a VFIO_USER_DMA_MAP message. +* *Count* is the size of the data to be transferred. +* *Data* is the data to be read or written. + +VFIO_USER_REGION_READ +--------------------- + +Message format +^^^^^^^^^^^^^^ + ++--------------+------------------------+ +| Name | Value | ++==============+========================+ +| Message ID | <ID> | ++--------------+------------------------+ +| Command | 8 | ++--------------+------------------------+ +| Message size | 32 + data size | ++--------------+------------------------+ +| Flags | Reply bit set in reply | ++--------------+------------------------+ +| Error | 0/errno | ++--------------+------------------------+ +| Read info | REGION read/write data | ++--------------+------------------------+ + +This command message is sent from the client to the server to read from server +memory. In the command messages, there is no data, and the count is the amount +of data to be read. The reply message must include the data read, and its count +field is the amount of data read. + +VFIO_USER_REGION_WRITE +---------------------- + +Message format +^^^^^^^^^^^^^^ + ++--------------+------------------------+ +| Name | Value | ++==============+========================+ +| Message ID | <ID> | ++--------------+------------------------+ +| Command | 9 | ++--------------+------------------------+ +| Message size | 32 + data size | ++--------------+------------------------+ +| Flags | Reply bit set in reply | ++--------------+------------------------+ +| Error | 0/errno | ++--------------+------------------------+ +| Write info | REGION read/write data | ++--------------+------------------------+ + +This command message is sent from the client to the server to write to server +memory. The command message must contain the data to be written, and its count +field must contain the amount of write data. The count field in the reply +message must be zero. + +VFIO_USER_DMA_READ +------------------ + +Message format +^^^^^^^^^^^^^^ + ++--------------+------------------------+ +| Name | Value | ++==============+========================+ +| Message ID | <ID> | ++--------------+------------------------+ +| Command | 10 | ++--------------+------------------------+ +| Message size | 28 + data size | ++--------------+------------------------+ +| Flags | Reply bit set in reply | ++--------------+------------------------+ +| Error | 0/errno | ++--------------+------------------------+ +| DMA info | DMA read/write data | ++--------------+------------------------+ + +This command message is sent from the server to the client to read from client +memory. In the command message, there is no data, and the count must will be +the amount of data to be read. The reply message must include the data read, +and its count field must be the amount of data read. + +VFIO_USER_DMA_WRITE +------------------- + +Message format +^^^^^^^^^^^^^^ + ++--------------+------------------------+ +| Name | Value | ++==============+========================+ +| Message ID | <ID> | ++--------------+------------------------+ +| Command | 11 | ++--------------+------------------------+ +| Message size | 28 + data size | ++--------------+------------------------+ +| Flags | Reply bit set in reply | ++--------------+------------------------+ +| Error | 0/errno | ++--------------+------------------------+ +| DMA info | DMA read/write data | ++--------------+------------------------+ + +This command message is sent from the server to the client to write to server +memory. The command message must contain the data to be written, and its count +field must contain the amount of write data. The count field in the reply +message must be zero. + +VFIO_USER_VM_INTERRUPT +---------------------- + +Message format +^^^^^^^^^^^^^^ + ++----------------+------------------------+ +| Name | Value | ++================+========================+ +| Message ID | <ID> | ++----------------+------------------------+ +| Command | 12 | ++----------------+------------------------+ +| Message size | 20 | ++----------------+------------------------+ +| Flags | Reply bit set in reply | ++----------------+------------------------+ +| Error | 0/errno | ++----------------+------------------------+ +| Interrupt info | <interrupt> | ++----------------+------------------------+ + +This command message is sent from the server to the client to signal the device +has raised an interrupt. + +Interrupt info format +^^^^^^^^^^^^^^^^^^^^^ + ++-----------+--------+------+ +| Name | Offset | Size | ++===========+========+======+ +| Sub-index | 16 | 4 | ++-----------+--------+------+ + +* *Sub-index* is relative to the IRQ index, e.g., the vector number used in PCI + MSI/X type interrupts. + +VFIO_USER_DEVICE_RESET +---------------------- + +Message format +^^^^^^^^^^^^^^ + ++--------------+------------------------+ +| Name | Value | ++==============+========================+ +| Message ID | <ID> | ++--------------+------------------------+ +| Command | 13 | ++--------------+------------------------+ +| Message size | 16 | ++--------------+------------------------+ +| Flags | Reply bit set in reply | ++--------------+------------------------+ +| Error | 0/errno | ++--------------+------------------------+ + +This command message is sent from the client to the server to reset the device. + +VFIO_USER_DIRY_PAGES +-------------------- + +Message format +^^^^^^^^^^^^^^ + ++--------------------+------------------------+ +| Name | Value | ++====================+========================+ +| Message ID | <ID> | ++--------------------+------------------------+ +| Command | 14 | ++--------------------+------------------------+ +| Message size | 16 | ++--------------------+------------------------+ +| Flags | Reply bit set in reply | ++--------------------+------------------------+ +| Error | 0/errno | ++--------------------+------------------------+ +| VFIO Dirty bitmap | <dirty bitmap> | ++--------------------+------------------------+ + +This command is analogous to VFIO_IOMMU_DIRTY_PAGES. It is sent by the client +to the server in order to control logging of dirty pages, usually during a live +migration. The VFIO dirty bitmap structure is defined in ``<linux/vfio.h>`` +(``struct vfio_iommu_type1_dirty_bitmap``). + +VFIO Dirty Bitmap Format +^^^^^^^^^^^^^^^^^^^^^^^^ + ++-------+--------+-----------------------------------------+ +| Name | Offset | Size | ++=======+========+=========================================+ +| argsz | 0 | 4 | ++-------+--------+-----------------------------------------+ +| flags | 4 | 4 | ++-------+--------+-----------------------------------------+ +| | +-----+----------------------------------------+ | +| | | Bit | Definition | | +| | +=====+========================================+ | +| | | 0 | VFIO_IOMMU_DIRTY_PAGES_FLAG_START | | +| | +-----+----------------------------------------+ | +| | | 1 | VFIO_IOMMU_DIRTY_PAGES_FLAG_STOP | | +| | +-----+----------------------------------------+ | +| | | 2 | VFIO_IOMMU_DIRTY_PAGES_FLAG_GET_BITMAP | | +| | +-----+----------------------------------------+ | ++-------+--------+-----------------------------------------+ +| data | 8 | 4 | ++-------+--------+-----------------------------------------+ + +* *argsz* is the size of the VFIO dirty bitmap info structure. + +* *flags* defines the action to be performed by the server: + + * *VFIO_IOMMU_DIRTY_PAGES_FLAG_START* instructs the server to start logging + pages it dirties. Logging continues until explicitly disabled by + VFIO_IOMMU_DIRTY_PAGES_FLAG_STOP. + + * *VFIO_IOMMU_DIRTY_PAGES_FLAG_STOP* instructs the server to stop logging + dirty pages. + + * *VFIO_IOMMU_DIRTY_PAGES_FLAG_GET_BITMAP* requests from the server to return + the dirty bitmap for a specific IOVA range. The IOVA range is specified by + "VFIO dirty bitmap get" structure, which must immediatelly follow the + "VFIO dirty bitmap" structure, explained next. This operation is only valid + if logging of dirty pages has been previously started. The server must + respond the same way it does for VFIO_USER_DMA_UNMAP (the dirty pages + bitmap must follow the response header). + + These flags are mutually exclusive with each other. + +* *data* This field is unused in vfio-user. + +VFIO Dirty Bitmap Get Format +^^^^^^^^^^^^^^^^^^^^^^^^^^^^ + ++--------+--------+------+ +| Name | Offset | Size | ++========+========+======+ +| iova | 0 | 8 | ++--------+--------+------+ +| size | 8 | 8 | ++--------+--------+------+ +| bitmap | 16 | 24 | ++--------+--------+------+ + +* *iova* is the IOVA offset + +* *size* is the size of the IOVA region + +* *bitmap* is the VFIO bitmap (``struct vfio_bitmap``), with the same semantics + as VFIO_USER_DMA_UNMAP. + + +Appendices +========== + +Unused VFIO ioctl() commands +---------------------------- + +The following VFIO commands do not have an equivalent vfio-user command: + +* VFIO_GET_API_VERSION +* VFIO_CHECK_EXTENSION +* VFIO_SET_IOMMU +* VFIO_GROUP_GET_STATUS +* VFIO_GROUP_SET_CONTAINER +* VFIO_GROUP_UNSET_CONTAINER +* VFIO_GROUP_GET_DEVICE_FD +* VFIO_IOMMU_GET_INFO + +However, once support for live migration for VFIO devices is finalized some +of the above commands may have to be handled by the client in their +corresponding vfio-user form. This will be addressed in a future protocol +version. + +VFIO groups and containers +^^^^^^^^^^^^^^^^^^^^^^^^^^ + +The current VFIO implementation includes group and container idioms that +describe how a device relates to the host IOMMU. In the vfio-user +implementation, the IOMMU is implemented in SW by the client, and is not +visible to the server. The simplest idea would be that the client put each +device into its own group and container. + +Backend Program Conventions +--------------------------- + +vfio-user backend program conventions are based on the vhost-user ones. + +* The backend program must not daemonize itself. +* No assumptions must be made as to what access the backend program has on the + system. +* File descriptors 0, 1 and 2 must exist, must have regular + stdin/stdout/stderr semantics, and can be redirected. +* The backend program must honor the SIGTERM signal. +* The backend program must accept the following commands line options: + + * ``--socket-path=PATH``: path to UNIX domain socket, + * ``--fd=FDNUM``: file descriptor for UNIX domain socket, incompatible with + ``--socket-path`` +* The backend program must be accompanied with a JSON file stored under + ``/usr/share/vfio-user``. -- 2.12.2
