Introduction

OpenVMM is a modular, cross-platform, general-purpose Virtual Machine Monitor (VMM), written in Rust.

The project is open-source, MIT Licensed, and developed publicly at microsoft/openvmm on GitHub.

Cross-Platform

OpenVMM supports a variety of host operating systems, architectures, and virtualization backends:

General Purpose

Similar to other general-purpose VMMs (such as Hyper-V, QEMU, VirtualBox), OpenVMM is able to host a wide variety of both modern and legacy guest operating systems on-top of its flexible virtual hardware platform.

• Modern operating systems can boot via UEFI, and interface with a wide selection of paravirtualized devices for services like networking, storage, and graphics.

• Legacy x86 operating systems can boot via BIOS, and are presented with a PC-compatible emulated device platform which includes legacy hardware such as IDE hard-disk/optical drives, floppy disk drives, and VGA graphics cards.

OpenVMM is regularly tested to ensure compatibility with popular operating systems (such as Windows, Linux, and FreeBSD), and strives to maintain reasonable compatibility with other, more niche/legacy operating systems as well.

Modular

OpenVMM is designed from the ground up to support a wide variety of distinct virtualization scenarios, each with their own unique needs and constraints.

Rather than relying on a "one size fits all" solution, the OpenVMM project enables users to build specialized versions of OpenVMM with the precise set of features required to power their particular scenario.

For example: A build of OpenVMM designed to run on a user's personal PC might compile-in all available features, in order support a wide variety of workloads, whereas a build of OpenVMM designed to run linux container workloads might opt for a narrow set of enabled features, in order to minimize resource consumption and VM-visible surface area.

One particularly notable use-case of OpenVMM is in OpenHCL (AKA, OpenVMM as a paravisor).

Unlike in traditional virtualization, where a VMM runs in a privileged host/root partition and provides virtualization services to a unprivileged guest partition, the "paravisor" model enables a VMM to provide virtualization services from within the guest partition itself.

It can be considered a form of "virtual firmware", running at a higher privilege level than the primary guest OS.

Paravisors are quite exciting, as they enable a wide variety of useful and novel virtualization scenarios! For example: at Microsoft, OpenHCL plays a key role in enabling several important Azure scenarios:

• Enabling existing workloads to seamlessly leverage Azure Boost (Azure's next-generation hardware accelerator), without requiring any modifications to the guest VM image.

• Enabling existing guest operating systems to run inside hardware-backed Confidential VMs.

• Powering Trusted Launch VMs - VMs that support Secure Boot, and include a vTPM.

To learn more about different facets of the OpenVMM project, check out the following links: