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Everything you wanted to know about Kernel-based Virtual Machine, but were afraid to ask
By Jon Benedict, oVirt Board of Directors and NetApp and Denise Ridolfo, Open Virtualization Alliance Governing Member, NetApp.
What is KVM? KVM (short for Kernel-based Virtual Machine) refers to a set of open source kernel modules that turns the Linux kernel into a hypervisor. It requires the use of CPU extensions that are available in both Intel and AMD CPU’s. As such, KVM provides “full virtualization”, as opposed to para-virtualized virtualization.
Because it is part of the Linux kernel, as opposed to a separate layer above an operating system, it is a “type 1” or “bare-metal hypervisor.” Avi Kivity and others originally created KVM at Qumranet and it was officially accepted into the upstream Linux kernel in February of 2007, as part of the 2.6.20 kernel release. Red Hat subsequently purchased Qumranet in 2008.
KVM was designed from the ground up to be a secure and high performance hypervisor. To that end, KVM takes advantages of things that the Linux kernel already does well on it’s own such as memory management, driver support, security, scheduling, and
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www.dcseurope.info I February 2014
other things. KVM simply adds in the missing components necessary to virtualize servers and/or desktops.
Acceptance into the Linux kernel is an important distinction to make for a few reasons. Architecturally speaking, this makes it much easier to take advantage of new kernel features and fixes.
As these features such as enhanced security, bug fixes, and hardware enablement are added, KVM can use them almost immediately. This is in stark contrast to other hypervisors that remain a separate layer and require guest kernel modification or recompiling of the host kernel in order to take full advantage of features. Under KVM, one can run multiple virtual machines running unmodified Linux, UNIX, or Windows guests.
Being part of the Linux kernel also means that a data center can use the same Linux operating system for virtual and native workloads. This cuts down on training
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