GitHub - mistivia/mvvmm: a small kvm-based virtual machine monitor

4 min read Original article ↗

MVVMM – Minimal Viable Virtual Machine Monitor

License: GPL v3 Platform: Linux Arch: x86_64 Requires: KVM

A virtual machine monitor (VMM) built upon KVM, designed for experimentation and learning.

Features:

  • Boot Linux with minimal overhead
  • Virtio‑based block and network devices
  • Graceful shutdown via guest module
  • Performance optimizations: irqfd, ioeventfd, virtqueue interrupt suppression
  • Run AI agents (Codex, Claude Code, OpenClaw, etc.)

Table of Contents

Quick Start

For a quick test, follow these steps:

  1. Clone the repository and build the VMM:
git clone --depth 1 https://github.com/mistivia/mvvmm
cd mvvmm
make

  1. Prepare a Linux kernel with VirtIO‑MMIO support (see Creating a Guest for details).

  2. Create a disk image (Alpine Linux minirootfs for example) and a simple initramfs.

  3. Run the VM:

./mvvmm -k vmlinuz -i initrd -d disk.img -t tap0

The following sections provide detailed instructions for each step.

Prerequisites

  • A Linux host with KVM support (/dev/kvm accessible)
  • GCC, Make, and standard build tools
  • Root privileges for network setup and disk mounting
  • Enough RAM and disk space for the guest

Building

Compile mvvmm with a single command:

The binary mvvmm will be produced in the current directory.

Creating a Guest

1. Linux Kernel

Download and build a recent Linux kernel (6.18.9 used in this example):

wget https://cdn.kernel.org/pub/linux/kernel/v6.x/linux-6.18.9.tar.xz
tar -xf linux-6.18.9.tar.xz
cd linux-6.18.9

Enable the necessary VirtIO‑MMIO options:

make defconfig
make menuconfig

Search for and enable:

  • CONFIG_VIRTIO_MMIO
  • CONFIG_VIRTIO_MMIO_CMDLINE_DEVICES

Then compile the kernel:

make -j$(nproc)
cp arch/x86/boot/bzImage ../vmlinuz
cd ..

2. Initial RAM Disk (initrd)

Create a minimal initramfs with BusyBox:

wget https://busybox.net/downloads/binaries/1.35.0-x86_64-linux-musl/busybox
mkdir -p initramfs/bin
chmod +x busybox
./busybox --install initramfs/bin/

Write an init script at initramfs/init:

#!/bin/sh

mount -t devtmpfs devtmpfs /dev
mount -t proc proc /proc
mount -t sysfs sys /sys
mkdir -p /dev/pts
mount -t devpts devpts /dev/pts
mdev -s

mkdir /sysroot
mount /dev/vda /sysroot
mount --move /dev /sysroot/dev
mount --move /proc /sysroot/proc
mount --move /sys /sysroot/sys

ip link set eth0 up
ip addr add 192.168.200.2/24 dev eth0
ip route add default via 192.168.200.1

exec chroot /sysroot /sbin/init

Make it executable and pack the initrd:

cd initramfs
chmod +x init
find . -print0 | cpio --null -ov --format=newc | gzip > ../initrd
cd ..

3. Disk Image

Create a sparse disk image and install Alpine Linux:

dd if=/dev/zero of=disk.img bs=1 count=0 seek=15G
mkfs.ext4 disk.img
mkdir mnt
sudo mount disk.img ./mnt

Extract Alpine minirootfs:

cd mnt
wget https://dl-cdn.alpinelinux.org/alpine/v3.23/releases/x86_64/alpine-minirootfs-3.23.3-x86_64.tar.gz
tar -xf alpine-minirootfs-3.23.3-x86_64.tar.gz
cd ..

Chroot into the image for basic setup:

sudo chroot ./mnt
export PATH=/bin:/sbin:$PATH
passwd
echo 'nameserver 8.8.8.8' > ./etc/resolv.conf
apk add openrc fastfetch

Enable serial console by uncommenting the following line in /etc/inittab:

ttyS0::respawn:/sbin/getty -L 115200 ttyS0 vt100

Exit chroot and unmount:

4. Network Setup

Create a TAP device and enable NAT:

ip tuntap add dev tap0 mod tap
ip link set dev tap0 up
ip addr add 192.168.200.1/24 dev tap0

sysctl -w net.ipv4.ip_forward=1
iptables -A FORWARD -i tap0 -j ACCEPT
iptables -A FORWARD -o tap0 -j ACCEPT
iptables -t nat -A POSTROUTING -o [YOUR_INTERNET_INTERFACE] -j MASQUERADE

Replace [YOUR_INTERNET_INTERFACE] with your host's outward‑facing interface (e.g., eth0, wlan0).

Running the VM

Launch the virtual machine with the kernel, initrd, disk image, and TAP device:

./mvvmm -k vmlinuz -i initrd -d disk.img -t tap0

You will see the serial console. Log in with the root password you set during the chroot step.

Once logged in, you can run fastfetch to verify the system is operational.

To shut down the guest, issue:

Then press Ctrl+A Ctrl+C in the terminal to exit the VMM.

Power Management

mvvmm does not have ACPI. A small Linux kernel module (guest-module/) handles poweroff and graceful shutdown.

When the host receives SIGTERM, the guest module will shut down the guest gracefully.

Reboot is not supported; restart the virtual machine process if you need to reboot.

Screenshot

image