6: Hybrid methods: KVM

To improve performance of desktop virtualization systems following the software/userspace paradigma there was the idea to move virtualization code into the Linux kernel:





There is still the normal Linux operating system running with all applications needed for work - but to access other systems you may start the "Kernel Virtual Machine" (KVM). This is a kernel module which does virtualization for you. It takes some amount of RAM for himself and runs virtual guest systems. Overhead is much smaller than in the normal software/userspace paradigma so performance is better.

If you are running a recent debian Linux system (as an example) you may just turn KVM on and create a virtual machine. No "Virtualization process" will appear in your process list as there is no such process running (outside of the kernel).

Redhat Inc. uses this technique to offer its own commercial virtualization system.

KVM also uses the Bochs Open Source BIOS (as in the xen HVM case) and the QEMU device emulators if no kvm guest drivers are present.

Examples of products following this paradigma:

• Redhat Enterprise Linux 5.4
• Debian Lenny

1. Why virtualization?
2. Userspace-based virtualization (the easy way)
3. Xen: Hypervisor-based virtualization
4. ESX: Hypervisor-based virtualization
   
5. Solaris Zones: A sharing approach
   
6. Hybrid methods: KVM