Cloud Hypervisor — Lightweight Virtual Machine Monitor in Rust

Introduction

Cloud Hypervisor is a virtual machine monitor (VMM) built on the rust-vmm project crates. It runs on Linux KVM and is designed for lightweight, secure VM execution in cloud infrastructure, offering a minimal codebase compared to QEMU while supporting essential cloud features like live migration and hotplug.

What Cloud Hypervisor Does

• Boots Linux and Windows guest VMs on KVM with minimal overhead
• Supports CPU, memory, disk, and network device hotplug
• Provides live migration for moving running VMs between hosts
• Exposes a REST API for programmatic VM lifecycle management
• Runs with a minimal device model to reduce attack surface

Architecture Overview

Cloud Hypervisor is built from modular rust-vmm crates: kvm-ioctls for KVM interaction, vm-memory for guest memory management, and virtio devices for I/O. The VMM process runs in user space, communicating with the kernel via KVM ioctls. A built-in HTTP API server allows external orchestrators to manage VM lifecycle.

Self-Hosting & Configuration

• Requires Linux with KVM support (Intel VT-x or AMD-V)
• Build with cargo; the binary has no runtime dependencies beyond KVM
• Configure VMs via command-line flags or the REST API
• Use cloud-init or ignition for guest OS provisioning
• Deploy behind orchestrators like Kata Containers or custom cloud platforms

Key Features

• Written in Rust for memory safety and reduced vulnerability surface
• Fast VM boot times (under 100ms for microVM workloads)
• CPU and memory hotplug for elastic scaling
• Live migration support for zero-downtime maintenance
• Virtio device model for efficient I/O

Comparison with Similar Tools

• QEMU — full-featured with broad hardware emulation; Cloud Hypervisor is leaner and Rust-native
• Firecracker — microVM focus with minimal device model; Cloud Hypervisor adds hotplug and live migration
• crosvm — Chrome OS VM monitor; Cloud Hypervisor targets cloud infrastructure
• NEMU — Intel's stripped QEMU fork; Cloud Hypervisor is a ground-up Rust implementation

FAQ

Q: Can Cloud Hypervisor run Windows guests? A: Yes. It supports Windows guests with virtio drivers for disk and network.

Q: How does it compare to Firecracker in performance? A: Boot times and overhead are similar. Cloud Hypervisor adds features like hotplug and live migration that Firecracker intentionally omits.

Q: Does it support GPU passthrough? A: VFIO-based PCI device passthrough is supported, enabling GPU and other device passthrough.

Q: Who uses Cloud Hypervisor? A: It is used in Microsoft Azure and other cloud platforms as a lightweight VMM for container and VM workloads.

Sources

• https://github.com/cloud-hypervisor/cloud-hypervisor
• https://www.cloudhypervisor.org/