We are pleased to announce the release of the Project ACRN hypervisor version 2.7.

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 v2.7 GitHub release page) or use Git clone and checkout commands:

git clone
cd acrn-hypervisor
git checkout v2.7

The project’s online technical documentation is also tagged to correspond with a specific release: generated v2.7 documents can be found at Documentation for the latest development branch is found at

ACRN v2.7 requires Ubuntu 18.04. Follow the instructions in the Getting Started Guide to get started with ACRN.

What’s New in v2.7

API and Documentation Updates for User VM and Service VM Terminology

More often than not, the terms “UOS” and “SOS” referred to the User VM and Service VM components of an ACRN Hypervisor system and not to the VM’s OS. We’ve updated the hypervisor APIs and documentation to properly reflect these names and removed uses of UOS and SOS.

In the code, uses of uos and sos in names were changed to user_vm and service_vm respectively. When specifically referring to the OS of these VMs, we now use user_vm_os and service_vm_os. These changes appear throughout the C files, as well as in the .xml configuration files.

For example, here are examples of old and new names:

Old Name

New Name

#define SOS_SOCKET_PORT 0x2000




static uint16_t get_uos_count(void)

static uint16_t get_user_vm_count(void)

static uint16_t get_phy_addr(uint8_t uos_id, uint16_t vaddr)

static uint16_t get_phy_addr(uint8_t user_vmid, uint16_t vaddr)

Update Scenario Names

The pre-defined scenario names were changed to be indicative of their properties instead of an example use. The “industry” scenario is now called “shared”, the “logical partitioning” scenario is now called “partitioned”, and the “hybrid” scenario name remains the same.

Here are the three configuration scenarios:

  • Shared: The physical hardware resources can be shared among post-launched User VMs. The Service VM (Device Model) provides device emulation for the shared virtual devices.

  • Partitioned: The physical resources are strictly dedicated to individual pre-launched User VMs and there is no Service VM needed.

  • Hybrid: The physical resource are dedicated to pre-launched User VMs and the Service VM provides resource emulation and sharing for post-launched User VMs, all in the same system configuration.

User-Friendly VM names

Instead of using a UUID as the User VM identifier, we’re now using a user-friendly VM name.

Extend Use of CAT Cache Tuning to VMs

In previous releases, Cache Allocation Technology (vCAT) was available only at the hypervisor level and with per-VM granularity. In this v2.7 release, each VM with exclusive cache resources can partition its cache resources with per-thread granularity and allocate cache resources to prioritized tasks.

Expand Passthrough Device Use Cases to Pre-Launched VMs

We now allow pre-launched VMs (in partitioned or hybrid scenarios) to use graphics device passthrough for improved performance, a feature previously available to only post-launched VMs.

We’ve extended Trusted Platform Module (TPM) 2.0 and its associated resource passthrough to post-launched VMs.

Upgrading to v2.7 From Previous Releases

We highly recommended that you follow these instructions to upgrade to v2.7 from previous ACRN releases.

Generate New Board XML

Board XML files, generated by ACRN board inspector, contain board information that is essential to build ACRN. Compared to previous versions, ACRN v2.7 adds the following hardware information to board XMLs to support new features and fixes.

  • Always initialize hw_ignore when parsing DMAR.

The new board XML can be generated using the ACRN board inspector in the same way as ACRN v2.6. Refer to Using ACRN Configuration Toolset for a complete list of steps to deploy and run the tool.

Update Configuration Options

In v2.7, the following elements are added to scenario XML files.

The following elements were removed.

  • KATA_VM VM type.


Document Updates

We’ve updated references throughout the documentation to use “Service VM” and “User VM” instead of “SOS” and “UOS” respectively.

We’ve also made edits throughout the documentation to improve clarity, formatting, and presentation:

Fixed Issues Details

  • 6610 - [ConfigTool]Remove the restriction that SERIAL_CONSOLE needs to be ttys0, ttys1, ttys2 or ttys3

  • 6620 - [ConfigTool]pci devices’ io-ports passthrough

Known Issues