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ACRN v3.1 (Sep 2022)

We are pleased to announce the release of the Project ACRN hypervisor version 3.1.

ACRN is a flexible, lightweight reference hypervisor that is built with real-time and safety-criticality in mind. It is optimized to streamline embedded development through an open-source platform. See the What Is ACRN introduction for more information.

All project ACRN source code is maintained in the repository and includes folders for the ACRN hypervisor, the ACRN device model, tools, and documentation. You can download this source code either as a zip or tar.gz file (see the ACRN v3.1 GitHub release page) or use Git clone and checkout commands:

git clone
cd acrn-hypervisor
git checkout v3.1

The project’s online technical documentation is also tagged to correspond with a specific release: generated v3.1 documents can be found at Documentation for the latest development branch is found at

ACRN v3.1 requires Ubuntu 20.04. Follow the instructions in the Getting Started Guide to get started with ACRN.

What’s New in v3.1

More ACRN Configuration Improvements

Release v3.0 featured a new ACRN Configurator UI tool with a more intuitive design and workflow that simplifies getting the setup for the ACRN hypervisor right. With this v3.1 release, we’ve continued making improvements to the Configurator including more comprehensive error checking with more developer-friendly messages. You’ll also see additional advanced configuration settings for tuning real-time performance including Cache Allocation Technology (CAT) and vCPU affinity. Read more in the ACRN Configurator Tool and Scenario Configuration Options documents.

If you have feedback on this, or other aspects of ACRN, please share them on the ACRN users mailing list.

As with the v3.0 release, we’ve simplified installation of the Configurator by providing a Debian package that you can download from the ACRN v3.1 tag assets and install. See the Getting Started Guide for more information.

Improved Board Inspector Collection and Reporting

You run the ACRN Board Inspector tool to collect information about your target system’s processors, memory, devices, and more. The generated board XML file is used by the ACRN Configurator to determine which ACRN configuration options are possible, as well as possible values for target system resources. The v3.1 Board Inspector has improved scanning and provides more messages about potential issues or limitations of your target system that could impact ACRN configuration options.

The Board Inspector is updated to probe beyond CPUID information for Cache Allocation Technology (CAT) support and also detects availability of L3 CAT by accessing the CAT MSRs directly. Read more in Board Inspector Tool.

Sample Application with Two Post-Launched VMs

With this v3.1 release, we provide a follow-on Sample Application User Guide to the Getting Started Guide. This sample application shows how to create two VMs that are launched on your target system running ACRN. One VM is a real-time VM running cyclictest, an open-source application commonly used to measure latencies in real-time systems. This real-time VM (RT_VM) uses inter-VM shared memory (IVSHMEM) to send data to a second Human-Machine Interface VM (HMI_VM) that formats and presents the collected data as a histogram on a web page shown by a browser. This guide shows how to configure, create, and launch the two VM images that make up this application. Full code for the sample application is provided in the acrn-hypervisor GitHub repo misc/sample_application.

Multiple-Displays Support for VMs

The virtio-gpu mechanism is enhanced to support VMs with multiple displays.

Improved TSC Frequency Reporting

The hypervisor now reports Time Stamp Counter (TSC) frequency in KHz so that VMs can get that number without calibrating to a high precision timer.

Upgrading to v3.1 from Previous Releases

We recommend you generate a new board XML for your target system with the v3.1 Board Inspector. You should also use the v3.1 Configurator to generate a new scenario XML file and launch scripts. Scenario XML files and launch scripts created by previous ACRN versions will not work with the v3.1 ACRN hypervisor build process and could produce unexpected errors during the build.

Given the scope of changes for the v3.1 release, we have recommendations for how to upgrade from prior ACRN versions:

  1. Start fresh from our Getting Started Guide. This is the best way to ensure you have a v3.1-ready board XML file from your target system and generate a new scenario XML and launch scripts from the new ACRN Configurator that are consistent and will work for the v3.1 build system.

  2. Use the upgrader tool to attempt upgrading configuration files that worked with a release before v3.1. You’ll need the matched pair of scenario XML and launch XML files from a prior configuration, and use them to create a new merged scenario XML file. See Upgrading ACRN Configurations to Recent Releases for details.

  3. Manually edit your prior scenario XML and launch XML files to make them compatible with v3.1. This is not our recommended approach.

Here are some additional details about upgrading to the v3.1 release.

Generate New Board XML

Board XML files, generated by ACRN Board Inspector, contain board information that is essential for building the ACRN hypervisor and setting up User VMs. Compared to previous versions, ACRN v3.1 adds the following information to the board XML file for supporting new features and fixes:

  • Probe and detect availability of L3 CAT by accessing the CAT MSRs directly

  • Refactor MSR utilities

  • Record all details from the real-time configuration table (RTCT) in the board XML and generate vRTCT instead of copying a physical one

The v3.1 Board Inspector includes a progress bar and timeout mechanism, as well as more developer-friendly logs and error messages. See the Board Inspector Tool documentation for a complete list of steps to install and run the tool.

Update Configuration Options

As explained in this Upgrading ACRN Configurations to Recent Releases document, we do provide a tool that can assist upgrading your existing pre-v3.1 scenario XML files in the new merged v3.1 format. From there, you can use the v3.1 ACRN Configurator to open the upgraded scenario file for viewing and further editing if the upgrader tool lost meaningful data during the conversion.

As part of the developer experience improvements to ACRN configuration, the following XML elements were refined in the scenario XML file:




See the Scenario Configuration Options documentation for details about all the available configuration options in the new Configurator.

Document Updates

Sample Application User Guide

The new Sample Application User Guide documentation shows how to configure, build, and run a practical application with a Real-Time VM and Human-Machine Interface VM that communicate using inter-VM shared memory.

We’ve also made edits throughout the documentation to improve clarity, formatting, and presentation. We started updating feature enabling tutorials based on the new Configurator, and will continue updating them after the v3.1 release (in the latest documentation). Here are some of the more significant updates:

Fixed Issues Details

  • #8162 - dm: virtio-blk parameter error

  • #8125 - [hypercube][ADL]Assertion’0’ failed found during hypercube_PIO_SCAN testing

  • #8111 - [life_mngr] Sync between SOS and RTVM failed when startup hence life_mngr cannot work

  • #7948 - Tiger Lake product with CAT enabled needed

  • #8063 - Need to generate config_summary.rst

  • #8098 - configurator build has dependency on published release documentation

  • #8087 - ACRN Configurator enable RDT and CDP after launch scenario

  • #8066 - User VM doesn’t have IP if launched by acrnd with virtio-net

  • #7563 - [ADL-S][SSRAM]RTCM Unit run failed with 2G memory size

  • #8068 - [config_tool] Imported scenarios not populating CAT widget

  • #7973 - config-tools: User concern about the progress of generating board.xml and not sure whether need exit after waiting some time.

  • #7975 - GSG python package xmlschema/elementpath incompatibility

  • #8050 - config_tools: cpu affinity

  • #8051 - ADL-S][S5]Can’t shutdown WaaG with user VM name same as in launch script

  • #8046 - [config_tool] Configurator creates duplicate VM name

  • #8018 - config-tools: default value & MAX_PCI_BUS_NUM

  • #7991 - [Workshop] Configurator create scenario popup window disappear sometimes.

  • #8033 - [config_tool] vUART widget address for pre-launched VM doesn’t update or display error

  • #8000 - [config_tool] Real-time vCPU checkbox is confusing to users

  • #7898 - [config_tool] Warning message when users attempt to create a new scenario or import an existing scenario for an existing configuration

  • #5692 - Keep Open: Used when updating config option documentation in .xsd files

  • #7914 - [config_tool] Focus change to new VM when added

  • #7661 - config-tools: Change MCE AC and UC (GP) to enable

  • #7927 - [acrn-configuration-tool] ACRN-Configurator does not consider L3 CAT config when opening an exiting configuration

  • #7958 - [configurator] Need highlight success or fail status in the popup window of save scenario button

  • #7913 - config-tools: build acrn successfully even set the same memory address between the pre vm 0 and hv

  • #7931 - Improve HV console as a bash-like one

  • #7960 - dm cannot stop correctly

  • #7935 - Build EFI-Stub fail

  • #7921 - [config_tool] Cache widget: Instructions missing for L2-only users

  • #7925 - [configurator] invalid virtual bdf in ivshmem could be saved

  • #7942 - [config_tool] vUART and IVSHMEM widgets don’t generate address

  • #7947 - Need optimize user flow to configure SSRAM for pre-launched RTVM

  • #7944 - Service VM hang when reboot user VM

  • #7940 - DM: add support for iothread

  • #7933 - [config_tool] Add tooltips to CPU affinity virtio

  • #7926 - [acrn-configuration-tool]Memory warning when build ACRN for WHL

  • #7902 - coding style cleanup in pci.c

  • #7917 - [config_tool] Order of plus and minus icons is inconsistent

  • #7790 - User VM fail to get IP with vhost net

  • #7759 - ERROR: LeakSanitizer: detected memory leaks found when run

  • #7915 - [config_tool] Duplicate VM error message - add spacing

  • #7906 - config-tools: Board inspector crashed when command line is too long in dmesg

  • #7907 - RRSBA should be disabled on platform using retpoline if enumerated

  • #7897 - [config_tool] Placement of plus icon for virtio

  • #7582 - configurator: board name truncated incorrectly

  • #7707 - configurator: IVSHMEM region name lacks pattern check

  • #7886 - config-tools: need to hide the ‘update-pciids: download failed’ message

  • #7559 - Copyright year range in code headers is not up to date

  • #7884 - config_tool: Move “BIOS Revision” line in Configurator UI

  • #7893 - [config_tool] Incompatibility with latest elementpath library

  • #7887 - hv: Surges of external interrupts may cause guest hang

  • #7880 - fail to run acrn-dm with wrong iasl path

Known Issues

  • #6631 - [KATA] Kata support is broken since v2.7

  • #6978 - openstack failed since ACRN v2.7

  • #7827 - [Configurator] Pre_launched standard VMs cannot share CPU with Service VM

  • #8202 - [HV][qemu0][v3.1]HV fail to boot acrn on qemu