Project 5: “Write a Simple Virtual Machine Monitor (VMM)” — Virtualization / CPU Architecture

A user-space VMM that uses Intel VT-x directly (via /dev/kvm or raw VMXON) to run guest code, handle VM exits, and emulate a minimal set of devices.

Quick Reference

Attribute Value
Primary Language See main guide
Alternative Languages N/A
Difficulty Expert
Time Estimate 1+ month
Knowledge Area See main guide
Tooling See main guide
Prerequisites Strong C, x86 assembly, OS internals, patience for hardware documentation

What You Will Build

A user-space VMM that uses Intel VT-x directly (via /dev/kvm or raw VMXON) to run guest code, handle VM exits, and emulate a minimal set of devices.

Why It Matters

This project builds core skills that appear repeatedly in real-world systems and tooling.

Core Challenges

  • Programming the VMCS fields correctly for guest/host state (maps to: VT-x internals)
  • Implementing EPT for memory virtualization (maps to: hardware-assisted memory virtualization)
  • Handling complex VM exits (CPUID, MSR access, I/O) (maps to: instruction emulation)
  • Making the guest actually boot a real kernel (maps to: full system emulation)

Key Concepts

  • Concept Resource
  • |———|———-|
  • VT-x architecture “Intel SDM Volume 3C, Chapter 23-33” - Intel (the definitive reference)
  • VMCS programming “Hypervisor From Scratch” tutorial series - Sina Karvandi
  • Extended Page Tables “Understanding the Linux Kernel” Hardware-Assisted Virtualization chapter - Bovet & Cesati
  • x86 system programming “Write Great Code, Volume 2” - Randall Hyde

Real-World Outcome

Deliver a working demo with observable output that proves the feature is correct.

Implementation Guide

  1. Reproduce the simplest happy-path scenario.
  2. Build the smallest working version of the core feature.
  3. Add input validation and error handling.
  4. Add instrumentation/logging to confirm behavior.
  5. Refactor into clean modules with tests.

Milestones

  • Milestone 1: Minimal working program that runs end-to-end.
  • Milestone 2: Correct outputs for typical inputs.
  • Milestone 3: Robust handling of edge cases.
  • Milestone 4: Clean structure and documented usage.

Validation Checklist

  • Output matches the real-world outcome example
  • Handles invalid inputs safely
  • Provides clear errors and exit codes
  • Repeatable results across runs

References

  • Main guide: VIRTUALIZATION_HYPERVISORS_HYPERCONVERGENCE.md
  • Primary references are listed in the main guide