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    Subject[PATCH v5 01/17] docs: acrn: Introduce ACRN
    Date
    From: Shuo Liu <shuo.a.liu@intel.com>

    Add documentation on the following aspects of ACRN:

    1) A brief introduction on the architecture of ACRN.
    2) I/O request handling in ACRN.

    To learn more about ACRN, please go to ACRN project website
    https://projectacrn.org, or the documentation page
    https://projectacrn.github.io/.

    Signed-off-by: Shuo Liu <shuo.a.liu@intel.com>
    Reviewed-by: Zhi Wang <zhi.a.wang@intel.com>
    Reviewed-by: Reinette Chatre <reinette.chatre@intel.com>
    Cc: Dave Hansen <dave.hansen@intel.com>
    Cc: Sen Christopherson <sean.j.christopherson@intel.com>
    Cc: Dan Williams <dan.j.williams@intel.com>
    Cc: Fengwei Yin <fengwei.yin@intel.com>
    Cc: Zhi Wang <zhi.a.wang@intel.com>
    Cc: Zhenyu Wang <zhenyuw@linux.intel.com>
    Cc: Yu Wang <yu1.wang@intel.com>
    Cc: Reinette Chatre <reinette.chatre@intel.com>
    Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
    Cc: Randy Dunlap <rdunlap@infradead.org>
    ---
    Documentation/virt/acrn/index.rst | 11 +++
    Documentation/virt/acrn/introduction.rst | 40 ++++++++++
    Documentation/virt/acrn/io-request.rst | 97 ++++++++++++++++++++++++
    Documentation/virt/index.rst | 1 +
    MAINTAINERS | 7 ++
    5 files changed, 156 insertions(+)
    create mode 100644 Documentation/virt/acrn/index.rst
    create mode 100644 Documentation/virt/acrn/introduction.rst
    create mode 100644 Documentation/virt/acrn/io-request.rst

    diff --git a/Documentation/virt/acrn/index.rst b/Documentation/virt/acrn/index.rst
    new file mode 100644
    index 000000000000..e3cf99033bdb
    --- /dev/null
    +++ b/Documentation/virt/acrn/index.rst
    @@ -0,0 +1,11 @@
    +.. SPDX-License-Identifier: GPL-2.0
    +
    +===============
    +ACRN Hypervisor
    +===============
    +
    +.. toctree::
    + :maxdepth: 1
    +
    + introduction
    + io-request
    diff --git a/Documentation/virt/acrn/introduction.rst b/Documentation/virt/acrn/introduction.rst
    new file mode 100644
    index 000000000000..6b44924d5c0e
    --- /dev/null
    +++ b/Documentation/virt/acrn/introduction.rst
    @@ -0,0 +1,40 @@
    +.. SPDX-License-Identifier: GPL-2.0
    +
    +ACRN Hypervisor Introduction
    +============================
    +
    +The ACRN Hypervisor is a Type 1 hypervisor, running directly on the bare-metal
    +hardware. It has a privileged management VM, called Service VM, to manage User
    +VMs and do I/O emulation.
    +
    +ACRN userspace is an application running in the Service VM that emulates
    +devices for a User VM based on command line configurations. ACRN Hypervisor
    +Service Module (HSM) is a kernel module in the Service VM which provides
    +hypervisor services to the ACRN userspace.
    +
    +Below figure shows the architecture.
    +
    +::
    +
    + Service VM User VM
    + +----------------------------+ | +------------------+
    + | +--------------+ | | | |
    + | |ACRN userspace| | | | |
    + | +--------------+ | | | |
    + |-----------------ioctl------| | | | ...
    + |kernel space +----------+ | | | |
    + | | HSM | | | | Drivers |
    + | +----------+ | | | |
    + +--------------------|-------+ | +------------------+
    + +---------------------hypercall----------------------------------------+
    + | ACRN Hypervisor |
    + +----------------------------------------------------------------------+
    + | Hardware |
    + +----------------------------------------------------------------------+
    +
    +ACRN userspace allocates memory for the User VM, configures and initializes the
    +devices used by the User VM, loads the virtual bootloader, initializes the
    +virtual CPU state and handles I/O request accesses from the User VM. It uses
    +ioctls to communicate with the HSM. HSM implements hypervisor services by
    +interacting with the ACRN Hypervisor via hypercalls. HSM exports a char device
    +interface (/dev/acrn_hsm) to userspace.
    diff --git a/Documentation/virt/acrn/io-request.rst b/Documentation/virt/acrn/io-request.rst
    new file mode 100644
    index 000000000000..79022a671ea7
    --- /dev/null
    +++ b/Documentation/virt/acrn/io-request.rst
    @@ -0,0 +1,97 @@
    +.. SPDX-License-Identifier: GPL-2.0
    +
    +I/O request handling
    +====================
    +
    +An I/O request of a User VM, which is constructed by the hypervisor, is
    +distributed by the ACRN Hypervisor Service Module to an I/O client
    +corresponding to the address range of the I/O request. Details of I/O request
    +handling are described in the following sections.
    +
    +1. I/O request
    +--------------
    +
    +For each User VM, there is a shared 4-KByte memory region used for I/O requests
    +communication between the hypervisor and Service VM. An I/O request is a
    +256-byte structure buffer, which is 'struct acrn_io_request', that is filled by
    +an I/O handler of the hypervisor when a trapped I/O access happens in a User
    +VM. ACRN userspace in the Service VM first allocates a 4-KByte page and passes
    +the GPA (Guest Physical Address) of the buffer to the hypervisor. The buffer is
    +used as an array of 16 I/O request slots with each I/O request slot being 256
    +bytes. This array is indexed by vCPU ID.
    +
    +2. I/O clients
    +--------------
    +
    +An I/O client is responsible for handling User VM I/O requests whose accessed
    +GPA falls in a certain range. Multiple I/O clients can be associated with each
    +User VM. There is a special client associated with each User VM, called the
    +default client, that handles all I/O requests that do not fit into the range of
    +any other clients. The ACRN userspace acts as the default client for each User
    +VM.
    +
    +Below illustration shows the relationship between I/O requests shared buffer,
    +I/O requests and I/O clients.
    +
    +::
    +
    + +------------------------------------------------------+
    + | Service VM |
    + |+--------------------------------------------------+ |
    + || +----------------------------------------+ | |
    + || | shared page ACRN userspace | | |
    + || | +-----------------+ +------------+ | | |
    + || +----+->| acrn_io_request |<-+ default | | | |
    + || | | | +-----------------+ | I/O client | | | |
    + || | | | | ... | +------------+ | | |
    + || | | | +-----------------+ | | |
    + || | +-|--------------------------------------+ | |
    + ||---|----|-----------------------------------------| |
    + || | | kernel | |
    + || | | +----------------------+ | |
    + || | | | +-------------+ HSM | | |
    + || | +--------------+ | | | |
    + || | | | I/O clients | | | |
    + || | | | | | | |
    + || | | +-------------+ | | |
    + || | +----------------------+ | |
    + |+---|----------------------------------------------+ |
    + +----|-------------------------------------------------+
    + |
    + +----|-------------------------------------------------+
    + | +-+-----------+ |
    + | | I/O handler | ACRN Hypervisor |
    + | +-------------+ |
    + +------------------------------------------------------+
    +
    +3. I/O request state transition
    +-------------------------------
    +
    +The state transitions of an ACRN I/O request are as follows.
    +
    +::
    +
    + FREE -> PENDING -> PROCESSING -> COMPLETE -> FREE -> ...
    +
    +- FREE: this I/O request slot is empty
    +- PENDING: a valid I/O request is pending in this slot
    +- PROCESSING: the I/O request is being processed
    +- COMPLETE: the I/O request has been processed
    +
    +An I/O request in COMPLETE or FREE state is owned by the hypervisor. HSM and
    +ACRN userspace are in charge of processing the others.
    +
    +4. Processing flow of I/O requests
    +-------------------------------
    +
    +a. The I/O handler of the hypervisor will fill an I/O request with PENDING
    + state when a trapped I/O access happens in a User VM.
    +b. The hypervisor makes an upcall, which is a notification interrupt, to
    + the Service VM.
    +c. The upcall handler schedules a tasklet to dispatch I/O requests.
    +d. The tasklet looks for the PENDING I/O requests, assigns them to different
    + registered clients based on the address of the I/O accesses, updates
    + their state to PROCESSING, and notifies the corresponding client to handle.
    +e. The notified client handles the assigned I/O requests.
    +f. The HSM updates I/O requests states to COMPLETE and notifies the hypervisor
    + of the completion via hypercalls.
    diff --git a/Documentation/virt/index.rst b/Documentation/virt/index.rst
    index de1ab81df958..c10b519507f5 100644
    --- a/Documentation/virt/index.rst
    +++ b/Documentation/virt/index.rst
    @@ -11,6 +11,7 @@ Linux Virtualization Support
    uml/user_mode_linux
    paravirt_ops
    guest-halt-polling
    + acrn/index

    .. only:: html and subproject

    diff --git a/MAINTAINERS b/MAINTAINERS
    index deaafb617361..e0fea5e464b4 100644
    --- a/MAINTAINERS
    +++ b/MAINTAINERS
    @@ -436,6 +436,13 @@ S: Orphan
    F: drivers/platform/x86/wmi.c
    F: include/uapi/linux/wmi.h

    +ACRN HYPERVISOR SERVICE MODULE
    +M: Shuo Liu <shuo.a.liu@intel.com>
    +L: acrn-dev@lists.projectacrn.org
    +S: Supported
    +W: https://projectacrn.org
    +F: Documentation/virt/acrn/
    +
    AD1889 ALSA SOUND DRIVER
    L: linux-parisc@vger.kernel.org
    S: Maintained
    --
    2.28.0
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