Kernel-based Virtual Machine (KVM) is a virtualization module in the

Linux kernel The Linux kernel is a free and open-source, monolithic, modular, multitasking, Unix-like operating system kernel. It was originally authored in 1991 by Linus Torvalds for his i386-based PC, and it was soon adopted as the kernel for the GNU ope ...

that allows the kernel to function as a hypervisor. It was merged into the

mainline Linux kernel The Linux kernel is a Free and open-source software, free and open-source, Monolithic kernel, monolithic, Modular programming, modular, Computer multitasking, multitasking, Unix-like operating system kernel (operating system), kernel. It was ori ...

in version 2.6.20, which was released on February 5, 2007. KVM requires a processor with hardware virtualization extensions, such as Intel VT or

AMD-V x86 virtualization is the use of hardware-assisted virtualization capabilities on an x86/x86-64 CPU. In the late 1990s x86 virtualization was achieved by complex software techniques, necessary to compensate for the processor's lack of hardware-as ...

. KVM has also been ported to other operating systems such as

FreeBSD FreeBSD is a free and open-source Unix-like operating system descended from the Berkeley Software Distribution (BSD), which was based on Research Unix. The first version of FreeBSD was released in 1993. In 2005, FreeBSD was the most popular ...

and illumos in the form of loadable kernel modules. KVM was originally designed for x86 processors but has since been ported to

S/390 The IBM System/390 is a discontinued mainframe product family implementing the ESA/390, the fifth generation of the System/360 instruction set architecture. The first computers to use the ESA/390 were the Enterprise System/9000 (ES/90 ...

PowerPC PowerPC (with the backronym Performance Optimization With Enhanced RISC – Performance Computing, sometimes abbreviated as PPC) is a reduced instruction set computer (RISC) instruction set architecture (ISA) created by the 1991 Apple Inc., App ...

, IA-64, and ARM. KVM provides hardware-assisted virtualization for a wide variety of guest operating systems including Linux,

BSD The Berkeley Software Distribution or Berkeley Standard Distribution (BSD) is a discontinued operating system based on Research Unix, developed and distributed by the Computer Systems Research Group (CSRG) at the University of California, Berk ...

Solaris Solaris may refer to: Arts and entertainment Literature, television and film * ''Solaris'' (novel), a 1961 science fiction novel by Stanisław Lem ** ''Solaris'' (1968 film), directed by Boris Nirenburg ** ''Solaris'' (1972 film), directed by ...

, Windows, Haiku,

ReactOS ReactOS is a free and open-source operating system for amd64/i686 personal computers intended to be binary-compatible with computer programs and device drivers made for Windows Server 2003 and later versions of Windows. ReactOS has been noted a ...

Plan 9 Plan 9 or Plan Nine may refer to: Music * Plan 9 (band), a psychedelic rock band from Rhode Island * ''Plan 9'', an album by Big Guitars From Memphis with Rick Lindy * "Plan 9", a song on the 1993 album ''Gorgeous'' by electronica band 808 Stat ...

, AROS Research Operating System and macOS. In addition, Android 2.2,

GNU/Hurd GNU Hurd is a collection of microkernel servers written as part of GNU, for the GNU Mach microkernel. It has been under development since 1990 by the GNU Project of the Free Software Foundation, designed as a replacement for the Unix kernel, and ...

(

Debian Debian (), also known as Debian GNU/Linux, is a Linux distribution composed of free and open-source software, developed by the community-supported Debian Project, which was established by Ian Murdock on August 16, 1993. The first version of D ...

K16), Minix 3.1.2a, Solaris 10 U3 and

Darwin Darwin may refer to: Common meanings * Charles Darwin (1809–1882), English naturalist and writer, best known as the originator of the theory of biological evolution by natural selection * Darwin, Northern Territory, a territorial capital city i ...

8.0.1, together with other operating systems and some newer versions of these listed, are known to work with certain limitations. Additionally, KVM provides paravirtualization support for Linux,

OpenBSD OpenBSD is a security-focused, free and open-source, Unix-like operating system based on the Berkeley Software Distribution (BSD). Theo de Raadt created OpenBSD in 1995 by forking NetBSD 1.0. According to the website, the OpenBSD project em ...

, FreeBSD,

NetBSD NetBSD is a free and open-source Unix operating system based on the Berkeley Software Distribution (BSD). It was the first open-source BSD descendant officially released after 386BSD was forked. It continues to be actively developed and is a ...

, Plan 9 and Windows guests using the VirtIO API. This includes a paravirtual

Ethernet card A network interface controller (NIC, also known as a network interface card, network adapter, LAN adapter or physical network interface, and by similar terms) is a computer hardware component that connects a computer to a computer network. Ear ...

, disk I/O controller,

balloon driver In computing, memory ballooning is a technique used to eliminate the need to overprovision host memory used by a virtual machine (VM). To implement it, the virtual machine's kernel implements a "balloon driver" which allocates unused memory within ...

, and a

VGA Video Graphics Array (VGA) is a video display controller and accompanying de facto graphics standard, first introduced with the IBM PS/2 line of computers in 1987, which became ubiquitous in the PC industry within three years. The term can now ...

graphics interface using SPICE or VMware drivers.

History

Avi Kivity began the development of KVM in mid-2006 at

Qumranet Qumranet, Inc. was an enterprise software company offering a desktop virtualization platform based on hosted desktops in Kernel-based Virtual Machines (KVM) on servers, linked with their SPICE protocol. The company was also the creator, maintainer ...

, a technology startup company that was acquired by

Red Hat Red Hat, Inc. is an American software company that provides open source software products to enterprises. Founded in 1993, Red Hat has its corporate headquarters in Raleigh, North Carolina, with other offices worldwide. Red Hat has become ass ...

in 2008. KVM surfaced in October, 2006 and 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.

Internals

KVM provides device abstraction but no processor emulation. It exposes the interface, which a user mode 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 system host. Originally a forked version of QEMU was provided to launch guests and deal with hardware emulation that isn't handled by the kernel. That support was eventually merged into the upstream project. There are now numerous Virtual Machine Monitors (VMMs) which can utilise the KVM interface including kvmtool, crosvm and Firecracker and numerous specialised VMMs build with frameworks such as rust-vmm. Internally, KVM uses SeaBIOS as an open source implementation of a 16-bit x86

BIOS In computing, BIOS (, ; Basic Input/Output System, also known as the System BIOS, ROM BIOS, BIOS ROM or PC BIOS) is firmware used to provide runtime services for operating systems and programs and to perform hardware initialization during the ...

Features

KVM has had support for hot swappable vCPUs, dynamic memory management, and Live Migration since February 2007. Memory write intensive workload impact in migration process

Emulated hardware

KVM itself emulates very little hardware, instead deferring to a higher level client application such as QEMU, crosvm, or Firecracker for device emulation. KVM provides the following emulated devices: * Virtual

CPU A central processing unit (CPU), also called a central processor, main processor or just processor, is the electronic circuitry that executes instructions comprising a computer program. The CPU performs basic arithmetic, logic, controlling, and ...

and memory * VirtIO

Graphical management tools

* Kimchi web-based virtualization management tool for KVM *

Virtual Machine Manager In computing, the Red Hat Virtual Machine Manager, also known as virt-manager, is a desktop virtual machine monitor. Features Virtual Machine Manager allows users to: * create, edit, start and stop VMs * view and control each VM's conso ...

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 Proxmox Virtual Environment (Proxmox VE or PVE) is an open-source software server for virtualization management. It is a hosted hypervisor that can run operating systems including Linux and Windows on x64 hardware. It is a Debian-based Lin ...

an open-source virtualization management package including KVM and

LXC Linux Containers (LXC) is an operating-system-level virtualization method for running multiple isolated Linux systems (containers) on a control host using a single Linux kernel. The Linux kernel provides the cgroups functionality that allows l ...

. It has a bare-metal installer, a web-based remote management GUI, a HA cluster stack, unified storage, flexible network, and optional commercial support. * OpenQRM management platform for managing heterogeneous data center infrastructures * GNOME Boxes Gnome interface for managing libvirt guests on Linux *

oVirt oVirt is a free, open-source virtualization management platform. It was founded by Red Hat as a community project on which Red Hat Virtualization is based. It allows centralized management of virtual machines, compute, storage and networking r ...

open-source virtualization management tool for KVM built on top of

libvirt libvirt is an open-source API, daemon and management tool for managing platform virtualization. It can be used to manage KVM, Xen, VMware ESXi, QEMU and other virtualization technologies. These APIs are widely used in the orchestration layer o ...

Licensing

The kernel-mode component of KVM is a part of

, itself licensed under GNU General Public License, version 2.

References

Bibliography

External links

*
Best practices for the Kernel-based Virtual Machine
IBM, second edition, April 2012
Virtio-blk Performance Improvement
KVM Forum 2012, November 8, 2012, by Asias He
Wikibook QEMU & KVM

crosvm - chrome OS virtual machine monitor

Firecracker VMM for KVM
{{DEFAULTSORT:Kernel-based Virtual Machine Free emulation software Free software programmed in C Free virtualization software Linux kernel features Virtualization software Virtualization software for Linux Red Hat software