kvm: Virtualization
KVM stands for Kernel-based Virtual Machine. It is a virtualization module that is deeply integrated into the Linux kernel. Instead of forming a separate virtualization layer, KVM uses the existing functionality of the kernel to run virtual machines. This means that KVM is not a standalone program, but a part of the kernel itself. When KVM is enabled, the Linux kernel turns into a hypervisor — a layer of software that can run multiple operating systems simultaneously on the same physical hardware. KVM makes this possible by using hardware virtualization extensions available on modern x86 processors, such as Intel VMX (Virtual Machine Extensions) and AMD SVM (Secure Virtual Machine).
The development of KVM began in mid-2006 at Qumranet, an Israeli startup. Avi Kivity was the lead developer who initiated the project. The goal was to build an efficient, performant and open source virtualization solution that would integrate well with Linux. Unlike other virtualization solutions of that time, such as Xen, which required a separate hypervisor, Kivity chose a different approach: using the Linux kernel itself as a basis. This led to a simpler architecture and better integration with existing system tools and security mechanisms.
On October 19, 2006, KVM was announced for the first time on the Linux Kernel Mailing List (LKML), the official forum for discussion about the development of the Linux kernel. The announcement was made by Avi Kivity, who introduced a patchset containing the first version of KVM. This first patchset only supported Intel VMX, which meant that KVM could initially only run on Intel processors with virtualization capability. Support for AMD SVM was added shortly afterwards, allowing KVM to be used on AMD processors as well. This expansion was crucial for the broader adoption of the technology, as it significantly increased hardware compatibility.
KVM was quickly taken seriously within the Linux community. The integration into the mainline kernel — the official, central version of the Linux kernel — took place in version 2.6.20. This version was released on February 5, 2007. From that moment on, KVM was officially part of every standard Linux distribution that used the latest kernel. This was an important milestone, because it meant that KVM was no longer an experimental or external module, but a standard component of the operating system. The first stable kernel version with KVM, often referred to as the “vanilla” kernel, also appeared in February 2007.
The integration into the mainline kernel accelerated the development and adoption of KVM. Developers from all over the world could now directly contribute to improving the virtualization functionality within Linux. Because KVM was part of the kernel, it could benefit from existing kernel mechanisms such as memory management, process scheduling and security. This provided a robust and reliable virtualization solution that scaled well on both desktops and servers.
In 2008, Red Hat acquired Qumranet. This acquisition was an important step for the further development and commercialization of KVM. Red Hat, one of the largest players in the enterprise Linux market, saw the potential of KVM as the basis for its own virtualization strategy. After the acquisition, Red Hat invested heavily in the development of KVM and made it the core of its virtualization and cloud solutions. Today, KVM is the basis of Red Hat Virtualization (RHV) and plays a central role in Red Hat OpenStack Platform.
KVM works in combination with QEMU, an emulator that emulates hardware. KVM handles the virtualization of the processor and memory, while QEMU handles the emulation of devices such as network cards, disks and graphics cards. This combination, often referred to as KVM/QEMU, forms a powerful and flexible virtualization solution. QEMU runs in userspace, while KVM works in the kernel. Communication between the two happens through a special interface, allowing virtual machines to run quickly and efficiently.
One of the first community events around KVM was the KVM Forum. The first KVM Forum took place from August 29 to 31, 2007 in Tucson, Arizona. This event brought together developers, companies and users to exchange knowledge about the technology, discuss new developments and determine the future of KVM. The forum marked the beginning of a lively and active community around KVM, which continues to grow to this day.
KVM supports a wide range of guest operating systems, including various Linux distributions, Microsoft Windows, and other Unix-like systems. Due to the close integration with the Linux kernel, the performance of virtual machines is often very close to that of physical hardware. This makes KVM suitable for both development environments and production clusters in data centers.
Another advantage of KVM is its open source nature. Because it is part of the Linux kernel, the source code is available to everyone. This encourages transparency, security and innovation. Organizations can inspect, modify and improve the code without licensing costs or dependence on a single vendor. This is in sharp contrast to closed virtualization solutions such as VMware ESXi.
KVM also plays an important role in modern cloud infrastructure. Many open source cloud platforms, such as OpenStack and oVirt, use KVM as the default hypervisor. This is because KVM is scalable, reliable and integrates well with other Linux-based tools and services. In large data centers, thousands of virtual machines can be managed via KVM, often in combination with orchestration tools such as Kubernetes or OpenShift.
There are also tools available that simplify interaction with KVM. One example is Snowglobe, a Linux program developed by Bilal Elmoussaoui. Snowglobe is a virtualization viewer that communicates with running QEMU instances via DBus. It offers support for keyboard, mouse and multi-touch gestures, allowing users to easily work with virtual machines. Snowglobe is available via Flatpak and is released under the GPL-3.0-or-later license. It is designed to be easy to use and to integrate well with modern Linux desktop environments.
Another example of user-friendly virtualization software is Boxes, a program that makes virtual machines easy for end users. Boxes uses KVM and QEMU under the hood, but hides the complexity behind a simple graphical interface. Users can download and install operating systems such as Fedora, Ubuntu or Windows with just a few clicks. Boxes also supports features such as snapshots, resource limits and USB passthrough, making it suitable for both learning and testing.
KVM has developed over more than fifteen years from an experimental project into one of the most widely used virtualization solutions in the world. Its success is due to the strong integration with Linux, the open source philosophy, and the support of large companies such as Red Hat. Over the years, KVM has continued to evolve with new functionalities such as live migration, PCI passthrough, and support for ARM processors.
Today, KVM is popular not only in data centers, but also on desktops and laptops. Many Linux users use KVM for testing software, running old applications, or safely isolating network activities. The combination of power, flexibility and openness makes KVM one of the most important pillars of modern virtualization and cloud computing.