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Yifan Liu d575edf79a hv: Change sched_event structure to resolve data race in event handling 
Currently the sched event handling may encounter data race problem, and
as a result some vcpus might be stalled forever.

One example can be wbinvd handling where more than 1 vcpus are doing
wbinvd concurrently. The following is a possible execution of 3 vcpus:
-------
0                            1                           2
                             req [Note: 0]
                             req bit0 set [Note: 1]
                             IPI -> 0
                             req bit2 set
                             IPI -> 2
                                                         VMExit
                                                         req bit2 cleared
                                                         wait
                                                         vcpu2 descheduled

VMExit
req bit0 cleared
wait
vcpu0 descheduled
                             signal 0
                             event0->set=true
                             wake 0

                             signal 2
                             event2->set=true [Note: 3]
                             wake 2
                                                         vcpu2 scheduled
                                                         event2->set=false
                                                         resume

                                                         req
                                                         req bit0 set
                                                         IPI -> 0
                                                         req bit1 set
                                                         IPI -> 1
                             (doesn't matter)
vcpu0 scheduled [Note: 4]
                                                         signal 0
                                                         event0->set=true
                                                         (no wake) [Note: 2]
event0->set=false                                        (the rest doesn't matter)
resume

Any VMExit
req bit0 cleared
wait
idle running

(blocked forever)

Notes:
0: req: vcpu_make_request(vcpu, ACRN_REQUEST_WAIT_WBINVD).
1: req bit: Bit in pending_req_bits. Bit0 stands for bit for vcpu0.
2: In function signal_event, At this time the event->waiting_thread
    is not NULL, so wake_thread will not execute
3: eventX: struct sched_event of vcpuX.
4: In function wait_event, the lock does not strictly cover the execution between
    schedule() and event->set=false, so other threads may kick in.
-----

As shown in above example, before the last random VMExit, vcpu0 ended up
with request bit set but event->set==false, so blocked forever.

This patch proposes to change event->set from a boolean variable to an
integer. The semantic is very similar to a semaphore. The wait_event
will add 1 to this value, and block when this value is > 0, whereas signal_event
will decrease this value by 1.

It may happen that this value was decreased to a negative number but that
is OK. As long as the wait_event and signal_event are paired and
program order is observed (that is, wait_event always happens-before signal_event
on a single vcpu), this value will eventually be 0.

Tracked-On: #6405
Signed-off-by: Yifan Liu <yifan1.liu@intel.com>
 		2021-08-20 08:11:40 +08:00
.github/ISSUE_TEMPLATE Update bug_report.md 2020-07-23 22:50:26 +08:00
devicemodel ACRN:DM: Fix the Null pointer error 2021-08-20 07:55:25 +08:00
doc doc: update configuration tool names 2021-08-19 16:34:08 -07:00
hypervisor hv: Change sched_event structure to resolve data race in event handling 2021-08-20 08:11:40 +08:00
misc config_tools: update lpc slot number in script 2021-08-20 08:07:43 +08:00
.checkpatch.conf checkpatch: fix the line limit back to 120 2018-10-29 14:10:22 +08:00
.clang-format config_tools: update clang-format file 2021-06-11 12:59:03 +08:00
.gitignore doc: update doc generation tooling to only work within the $BUILDDIR 2019-10-14 17:26:48 -04:00
CODEOWNERS doc: update CODEOWNERS for tech docs 2021-02-01 16:48:08 +08:00
LICENSE doc: update LICENSE copyright years 2020-12-18 15:12:18 +08:00
Makefile Makefile:add targz-pkg entry in Makefile 2021-08-09 11:52:27 +08:00
README.rst doc: Update address to report security vulnerability 2021-07-13 16:24:46 -07:00
VERSION version: 2.6-unstable 2021-06-25 14:45:38 +08:00
paths.make use variables for installation directories. 2020-06-05 15:25:12 +08:00

README.rst 

Project ACRN Embedded Hypervisor
################################


.. raw:: html

   <img src="doc/images/ACRN_Logo_PrimaryLockup_COLOR-300x300-1.png"
   height="175px" align="right">

The open source project ACRN defines a device hypervisor reference stack
and an architecture for running multiple software subsystems, managed
securely, on a consolidated system by means of a virtual machine
manager. It also defines a reference framework implementation for
virtual device emulation, called the "ACRN Device Model".

The ACRN Hypervisor is a Type 1 reference hypervisor stack, running
directly on the bare-metal hardware, and is suitable for a variety of
IoT and embedded device solutions. The ACRN hypervisor addresses the
gap that currently exists between datacenter hypervisors, and hard
partitioning hypervisors. The ACRN hypervisor architecture partitions
the system into different functional domains, with carefully selected
guest OS sharing optimizations for IoT and embedded devices.

.. start_include_here

Community Support
*****************

The Project ACRN Developer Community includes developers from member
organizations and the general community all joining in the development of
software within the project. Members contribute and discuss ideas,
submit bugs and bug fixes. They also help those in need
through the community's forums such as mailing lists and IRC channels. Anyone
can join the developer community and the community is always willing to help
its members and the User Community to get the most out of Project ACRN.

Welcome to the project ARCN community!

We're now holding weekly Technical Community Meetings and encourage you
to call in and learn more about the project. Meeting information is on
the `TCM Meeting page`_ in our `ACRN wiki <https://wiki.projectacrn.org/>`_.

.. _TCM Meeting page:
   https://github.com/projectacrn/acrn-hypervisor/wiki/ACRN-Committee-and-Working-Group-Meetings#technical-community-meetings

Resources
*********

Here's a quick summary of resources to find your way around the Project
ACRN support systems:

* **Project ACRN Website**: The https://projectacrn.org website is the
  central source of information about the project. On this site, you'll
  find background and current information about the project as well as
  relevant links to project material.  For a quick start, refer to the
  `Introduction`_ and `Getting Started Guide`_.

* **Source Code in GitHub**: Project ACRN source code is maintained on a
  public GitHub repository at https://github.com/projectacrn/acrn-hypervisor.
  You'll find information about getting access to the repository and how to
  contribute to the project in this `Contribution Guide`_ document.

* **Documentation**: Project technical documentation is developed
  along with the project's code, and can be found at
  https://projectacrn.github.io.  Additional documentation is maintained in
  the `Project ACRN GitHub wiki`_.

* **Issue Reporting and Tracking**: Requirements and Issue tracking is done in
  the Github issues system: https://github.com/projectacrn/acrn-hypervisor/issues.
  You can browse through the reported issues and submit issues of your own.

* **Reporting a Potential Security Vulnerability**: If you have discovered potential
  security vulnerability in ACRN, please send an e-mail to acrn-security@lists.projectacrn.org.

  It is important to include the following details:

  - The projects and versions affected
  - Detailed description of the vulnerability
  - Information on known exploits

* **Mailing List**: The `Project ACRN Development mailing list`_ is perhaps the most convenient
  way to track developer discussions and to ask your own support questions to
  the project ACRN community.  There are also specific `ACRN mailing list
  subgroups`_ for builds, users, and Technical
  Steering Committee notes, for example.
  You can read through the message archives to follow
  past posts and discussions, a good thing to do to discover more about the
  project.


.. _Introduction: https://projectacrn.github.io/latest/introduction/
.. _Getting Started Guide: https://projectacrn.github.io/latest/getting-started/
.. _Contribution Guide: https://projectacrn.github.io/latest/contribute.html
.. _Project ACRN GitHub wiki: https://github.com/projectacrn/acrn-hypervisor/wiki
.. _PGP Key: https://www.intel.com/content/www/us/en/security-center/pgp-public-key.html
.. _vulnerability handling guidelines:
   https://www.intel.com/content/www/us/en/security-center/vulnerability-handling-guidelines.html
.. _Project ACRN Development mailing list: https://lists.projectacrn.org/g/acrn-dev
.. _ACRN mailing list subgroups: https://lists.projectacrn.org/g/main/subgroups