OpenHCL Architecture

Prerequisites:

• Getting Started: OpenHCL.
• Architecture: OpenVMM Architecture.

This page is under construction

Overview

The following diagram offers a brief, high-level overview of the OpenHCL Architecture.

VTLs

OpenHCL currently relies on Hyper-V's implementation of Virtual Trust Levels (VTLs) to implement the security boundaries necessary for running OpenVMM as a paravisor.

VTLs can be backed by:

• Hardware-based TEEs, like Intel TDX and AMD SEV-SNP
• Software-based constructs, like Hyper-V VSM

OpenHCL runs within VTL2¹, and provides virtualization services to a Guest OS running in VTL0.

OpenHCL Linux

By building on-top of Linux, OpenHCL is able to leverage the extensive Linux software and development ecosystem, and avoid re-implementing various components like core OS primitives, device drivers, and software libraries. As a result: OpenHCL provides a familiar and productive environment for developers.

The OpenHCL Linux Kernel uses a minimal kernel configuration, designed to host a single specialized build of OpenVMM in userspace.

In debug configurations, userspace may include additional facilities (such as an interactive shell, additional perf and debugging tools, etc). Release configurations use a lean, minimal userspace, consisting entirely of OpenHCL components.

Scenario: Azure Boost Storage/Networking Translation

Traditionally, Azure VMs have used Hyper-V VMBus-based synthetic networking and synthetic storage for I/O. Azure Boost introduces hardware accelerated storage and networking. It exposes different interfaces to guest VMs for networking and storage. Specifically, it exposes a new proprietary Microsoft Azure Network Adapter (MANA) and an NVMe interface for storage.

OpenHCL is able to provide a compatibility layer for I/O virtualization on Azure Boost enabled systems.

Specifically, OpenHCL exposes Hyper-V VMBus-based synthetic networking and synthetic storage for I/O to the guest OS in a VM. OpenHCL then maps those synthetic storage and networking interfaces to the hardware accelerated interfaces provided by Azure Boost.

The following diagram shows a high level overview of how synthetic networking is supported in OpenHCL over Microsoft Azure Network Adapter (MANA)

The following diagram shows a high level overview of how accelerated networking is supported in OpenHCL over MANA