Kernel-based Virtual Machine

Kernel-based Virtual Machine (KVM) is a free and open-source virtualization module in the Linux kernel that allows the kernel to function as a hypervisor. It was merged into the mainline Linux kernel in version 2.6.20, which was released on February 5, 2007.[1] KVM requires a processor with hardware virtualization extensions, such as Intel VT or AMD-V.[2] KVM has also been ported to other operating systems such as FreeBSD[3] and illumos[4] in the form of loadable kernel modules.

Not to be confused with KVM switch.
KVM
Original author(s)Qumranet
Developer(s)The Linux Kernel community
Repository
Written inC
Operating systemUnix-like
PlatformARM, PowerPC, ESA/390, IA-32, x86-64
TypeHypervisor
LicenseGNU GPL or LGPL
Websitewww.linux-kvm.org

KVM was originally designed for x86 processors but has since been ported to ESA/390,[5] PowerPC,[6] IA-64, and ARM.[7] The IA-64 port was removed in 2014.[8]

KVM supports hardware-assisted virtualization for a wide variety of guest operating systems including BSD, Solaris, Windows, Haiku, ReactOS, Plan 9, AROS, macOS, and even other Linux systems.[9][10] In addition, Android 2.2, GNU/Hurd[11] (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.[12]

Additionally, KVM provides paravirtualization support for Linux, OpenBSD,[13] FreeBSD,[14] NetBSD,[15] Plan 9[16] and Windows guests using the VirtIO API.[17] This includes a paravirtual Ethernet card, disk I/O controller,[18] balloon driver, and a VGA graphics interface using SPICE or VMware drivers.

History

Avi Kivity began the development of KVM in mid-2006 at Qumranet, a technology startup company[19] that was acquired by Red Hat in 2008.[20]

KVM surfaced in October 2006[21] and was merged into the Linux kernel mainline in kernel version 2.6.20, which was released on 5 February 2007.[1]

KVM is maintained by Paolo Bonzini.[22]

Internals
A high-level overview of the KVM/QEMU virtualization environment[23]: 3 

KVM provides device abstraction but no processor emulation. It exposes the /dev/kvm 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.[24]

Features

KVM has had support for hot swappable vCPUs,[25] dynamic memory management,[26] and Live Migration since February 2007.[27][28] It also reduces the impact that memory write-intensive workloads have on the migration process.[29]

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:

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 LXC. 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 – open-source virtualization management tool for KVM built on top of libvirt

Licensing

The kernel-mode component of KVM is a part of Linux kernel, itself licensed under GNU General Public License, version 2.[31]

See also

References
  1. "Linux kernel 2.6.20, Section 2.2. Virtualization support through KVM". kernelnewbies.org. 2007-02-05. Retrieved 2014-06-16.
  2. KVM FAQ: What do I need to use KVM?
  3. "FreeBSD Quarterly Status Report: Porting Linux KVM to FreeBSD".
  4. "KVM on illumos".
  5. "Gmane - Mail To News And Back Again". Archived from the original on 2007-09-29. Retrieved 2007-05-07.
  6. Gmane Loom Archived 2007-09-29 at the Wayback Machine
  7. "KVM/ARM Open Source Project". Archived from the original on 2013-03-10. Retrieved 2017-11-01.
  8. "kernel/git/torvalds/linux.git: KVM: ia64: remove".
  9. "KVM wiki: Guest support status". Retrieved 2007-05-27.
  10. "Running Mac OS X as a QEMU/KVM Guest". Retrieved 2014-08-20.
  11. "status". Gnu.org. Retrieved 2014-02-12.
  12. "Guest Support Status - KVM". Linux-kvm.org. Retrieved 2014-02-12.
  13. "OpenBSD man page virtio(4)". Retrieved 2018-02-04.
  14. "virtio binary packages for FreeBSD". Retrieved 2012-10-29.
  15. "NetBSD man page virtio(4)". Archived from the original on 2019-11-13. Retrieved 2013-07-15.
  16. "plan9front". Retrieved 2013-02-11.
  17. "An API for virtual I/O: virtio". LWN.net. 2007-07-11. Retrieved 2014-04-16.
  18. "SCSI target for KVM wiki". linux-iscsi.org. 2012-08-07. Archived from the original on 2020-06-05. Retrieved 2012-08-12.
  19. Interview: Avi Kivity Archived 2007-04-26 at the Wayback Machine on KernelTrap
  20. "Red Hat Advances Virtualization Leadership with Qumranet, Inc. Acquisition". Red Hat. 4 September 2008. Retrieved 16 June 2015.
  21. "KVM 15 equipped with live migration | IT World Canada News". 7 March 2007.
  22. Libby Clark (7 April 2015). "Git Success Stories and Tips from KVM Maintainer Paolo Bonzini". Linux.com. Archived from the original on 15 March 2016. Retrieved 17 June 2015.
  23. Khoa Huynh; Stefan Hajnoczi (2010). "KVM/QEMU Storage Stack Performance Discussion" (PDF). IBM. Linux Plumbers Conference. Retrieved January 3, 2015.
  24. "SeaBIOS". seabios.org. 2013-12-21. Retrieved 2014-06-16.
  25. "Hot Plugging Virtual CPUs with Red Hat Enterprise Virtualization Manager".
  26. "Faq - KVM".
  27. "KVM-15 release [LWN.net]".
  28. "Migration - KVM".
  29. "Daniel P. Berrangé » Blog Archive » Analysis of techniques for ensuring migration completion with KVM".
  30. "The Definitive KVM (Kernel-based Virtual Machine) API Documentation — the Linux Kernel documentation".
  31. "Linux kernel licensing rules — The Linux Kernel documentation". www.kernel.org. Archived from the original on 7 March 2020. Retrieved 2020-01-06.

Bibliography


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