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docs: acrn: Introduce ACRN

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Add documentation on the following aspects of ACRN:

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

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

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>
Reviewed-by: Zhi Wang <zhi.a.wang@intel.com>
Reviewed-by: Reinette Chatre <reinette.chatre@intel.com>
Reviewed-by: Borislav Petkov <bp@suse.de>
Signed-off-by: Shuo Liu <shuo.a.liu@intel.com>
Link: https://lore.kernel.org/r/20210207031040.49576-2-shuo.a.liu@intel.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
This commit is contained in:
Shuo Liu 2021-02-07 11:10:23 +08:00 committed by Greg Kroah-Hartman
parent b212658aeb
commit c619a804cc
6 changed files with 206 additions and 0 deletions
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.. SPDX-License-Identifier: GPL-2.0
===============
ACRN CPUID bits
===============
A guest VM running on an ACRN hypervisor can check some of its features using
CPUID.
ACRN cpuid functions are:
function: 0x40000000
returns::
eax = 0x40000010
ebx = 0x4e524341
ecx = 0x4e524341
edx = 0x4e524341
Note that this value in ebx, ecx and edx corresponds to the string
"ACRNACRNACRN". The value in eax corresponds to the maximum cpuid function
present in this leaf, and will be updated if more functions are added in the
future.
function: define ACRN_CPUID_FEATURES (0x40000001)
returns::
ebx, ecx, edx
eax = an OR'ed group of (1 << flag)
where ``flag`` is defined as below:
================================= =========== ================================
flag value meaning
================================= =========== ================================
ACRN_FEATURE_PRIVILEGED_VM 0 guest VM is a privileged VM
================================= =========== ================================
function: 0x40000010
returns::
ebx, ecx, edx
eax = (Virtual) TSC frequency in kHz.

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.. SPDX-License-Identifier: GPL-2.0
===============
ACRN Hypervisor
===============
.. toctree::
:maxdepth: 1
introduction
io-request
cpuid

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.. SPDX-License-Identifier: GPL-2.0
ACRN Hypervisor Introduction
============================
The ACRN Hypervisor is a Type 1 hypervisor, running directly on 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.
The ACRN hypervisor is open for contribution from anyone. The source repo is
available at https://github.com/projectacrn/acrn-hypervisor.

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.. 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 worker to dispatch I/O requests.
d. The worker 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.

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@ -12,6 +12,7 @@ Linux Virtualization Support
paravirt_ops
guest-halt-polling
ne_overview
acrn/index
.. only:: html and subproject

7
MAINTAINERS
View File

@ -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