Kernel-based Virtual Machine

Kernel-based Virtual Machine (KVM) is a 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. KVM requires a processor with hardware virtualization extensions, such as Intel VT or AMD-V. KVM has also been ported to other operating systems such as FreeBSD and illumos in the form of loadable kernel modules.
KVM was originally designed for x86 processors but has since been ported to S/390, PowerPC, IA-64, and ARM.
KVM provides hardware-assisted virtualization for a wide variety of guest operating systems including Linux, BSD, Solaris, Windows, Haiku, ReactOS, Plan 9, AROS Research Operating System and macOS. 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.
Additionally, KVM provides paravirtualization support for Linux, OpenBSD, FreeBSD, NetBSD, Plan 9 and Windows guests using the VirtIO API. This includes a paravirtual Ethernet card, disk I/O controller, 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 that was acquired by Red Hat 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:
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.
Features.
KVM supports hot plug vCPUs, dynamic memory management, and Live Migration since February 2007. memory write intensive workload impacts 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:
Licensing.
The kernel-mode component of KVM is a part of Linux kernel, itself licensed under GNU General Public License, version 2.