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Subject[PATCH v4 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>
---
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..019dc5978f7c
--- /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 a 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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