Kernel-Based Virtual Machine

Kernel-based Virtual Machine (KVM) is a virtualization infrastructure for the Linux kernel that turns it into a hypervisor. It was merged into the Linux kernel mainline in kernel version 2.6.20, which was released on February 5, 2007. KVM requires a processor with hardware virtualization extension. KVM has also been ported to FreeBSD and illumos in the form of loadable kernel modules.

KVM originally supported x86 processors and has been ported to S/390, PowerPC, and IA-64. An ARM port was merged during the 3.9 kernel merge window.

A wide variety of guest operating systems work with KVM, including many flavours and versions of Linux, BSD, Solaris, Windows, Haiku, ReactOS, Plan 9, AROS Research Operating System and OS X. In addition, Android 2.2, GNU/Hurd (Debian K16), Minix 3.1.2a, Solaris 10 U3 and Darwin 8.0.1, together with other operating systems and some newer versions of these listed, are known to work with certain limitations.

Paravirtualization support for certain devices is available for Linux, OpenBSD, FreeBSD, NetBSD, Plan 9 and Windows guests using the VirtIO API. This supports a paravirtual Ethernet card, a paravirtual disk I/O controller, a balloon device for adjusting guest memory usage, and a VGA graphics interface using SPICE or VMware drivers.

Internals

A high-level overview of the KVM/QEMU virtualization environment^:3

By itself, KVM does not perform any emulation. Instead, it exposes the /dev/kvm interface, which a userspace host can then use to:

Set up the guest VM's address space. The host must also supply a firmware image (usually a custom BIOS when emulating PCs) that the guest can use to bootstrap into its main OS.
Feed the guest simulated I/O.
Map the guest's video display back onto the host.

On Linux, QEMU versions 0.10.1 and later is one such userspace host. QEMU uses KVM when available to virtualize guests at near-native speeds, but otherwise falls back to software-only emulation.

Internally, KVM uses SeaBIOS as an open source implementation of a 16-bit x86 BIOS.

Licensing

KVM's parts are licensed under various GNU licenses:

KVM kernel module: GPL v2
KVM user module: LGPL v2
QEMU virtual CPU core library (libqemu.a) and QEMU PC system emulator: LGPL
Linux user mode QEMU emulator: GPL
BIOS files (bios.bin, vgabios.bin and vgabios-cirrus.bin): LGPL v2 or later

History

Avi Kivity began the development of KVM at Qumranet, a technology startup company that was acquired by Red Hat in 2008.

KVM was merged into the Linux kernel mainline in kernel version 2.6.20, which was released on 5 February 2007.

KVM is maintained by Paolo Bonzini.

Graphical management tools

libvirt supports KVM

Kimchi – web-based virtualization management tool for KVM
Virtual Machine Manager – supports creating, editing, starting, and stopping KVM-based virtual machines, as well as live or cold drag-and-drop migration of VMs between hosts.
Proxmox Virtual Environment – an open-source virtualization management package including KVM and OpenVZ. It has a bare-metal installer, a web-based remote management GUI, and optional commercial support.
OpenQRM – management platform for managing heterogeneous data center infrastructures.
GNOME Boxes – Gnome interface for managing libvirt guests on Linux.
oVirt – open-source virtualization management tool for KVM built on top of libvirt

Emulated hardware

Class	Device
Video card	Cirrus CLGD 5446 PCI VGA card, dummy VGA card with Bochs VESA extensions, or Virgil as a virtual 3D GPU
PCI	i440FX host PCI bridge and PIIX3 PCI to ISA bridge
Input device	PS/2 Mouse and Keyboard
Sound card	Sound Blaster 16, ENSONIQ AudioPCI ES1370, Gravis Ultrasound GF1, CS4231A compatible
Ethernet Network card	AMD Am79C970A (Am7990), E1000 (Intel 82540EM, 82573L, 82544GC), NE2000, and Realtek RTL8139
Watchdog timer	Intel 6300ESB or IB700
RAM	between 50 MB and 32 TB
CPU	1 – 160 CPUs