For only being a release candidate the Linux 2.6.20 kernel has already generated quite a bit of attention. On top of adding asynchronous SCSI scanning, multi-threaded USB probing, and many driver updates, the Linux 2.6.20 kernel will include a full virtualization (not para-virtualization) solution. Kernel-based Virtual Machine (or KVM for short) is a GPL software project that has been developed and sponsored by Qumranet. In this article we are offering a brief overview of the Kernel-based Virtual Machine for Linux as well as offering up in-house performance numbers as we compare KVM to other virtualization solutions such as QEMU Accelerator and Xen.
What has been merged into the Linux 2.6.20 kernel is the device driver for managing the virtualization hardware. The other component that comprises KVM is the user-space program, which is a modified version of QEMU. Kernel-based Virtual Machine for Linux uses Intel Virtualization Technology (VT) and AMD Secure Virtual Machine (SVM/AMD-V) for hardware virtualization support. With that said, one of the presented hardware requirements to use KVM is an x86 processor with either of these technologies. The respective technologies are present in the Intel Core series and later, Xeon 5000 series and later, Xeon LV series, and AMD's Socket F and AM2 processors.
The Kernel-based Virtual Machine also assigns every virtual machine as a regular Linux process handled by the Linux scheduler by adding a guest mode execution. With the virtual machine being a standard Linux process, all standard process management tools can be used. The KVM kernel component is embedded into Linux 2.6.20-rc1 kernels and newer, but the KVM module can be built on older kernels (2.6.16 to 2.6.19) as well. At this stage, KVM supports Intel hosts, AMD hosts, Linux guests (x86 and x86_64), Windows guests (x86), SMP hosts, and non-live migration of guests. However, still being worked on is optimized MMU virtualization, live migration, and SMP guests. Microsoft Windows x64 does not work with KVM at this time.
Whether you are using a kernel with KVM built-in or loading it as a module, the process for setting up and running guest operating systems is quite easy. After setting up an image (qemu-img will work with KVM) and the KVM kernel component loaded, the modified version of QEMU can be used with the standard QEMU arguments to get you running.