Kernel-based Virtual Machine (KVM)

Kernel-based Virtual Machine is a virtualization module in the Linux kernel that allows the kernel to function as a hypervisor. 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 and 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 device, and a VGA graphics interface using SPICE or VMware drivers.

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.

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.

KVM supports hot plug vCPUs, dynamic memory management, and Live Migration since February 2007. Memory write intensive workload impacts in migration process.