Kernel-based Virtual Machine (KVM) represents a cutting-edge open-source virtualization technology seamlessly integrated into the Linux® operating system. With KVM, Linux transforms into a robust hypervisor that empowers a host machine to concurrently operate multiple self-contained virtual environments known as guests or virtual machines (VMs).

KVM is an integral component of Linux, available in Linux 2.6.20 and later versions. Its initial introduction dates back to 2006, followed by its seamless integration into the mainline Linux kernel approximately a year later. Leveraging its integration within the existing Linux codebase, KVM automatically inherits the benefits of each new Linux feature, fix, and advancement, obviating the need for additional engineering efforts

How does KVM work?

By utilizing KVM, Linux undergoes a remarkable transformation into a type-1 (bare-metal) hypervisor. Hypervisors, regardless of type, rely on certain operating system-level elements to facilitate the execution of virtual machines (VMs). 

These components include a memory manager, process scheduler, input/output (I/O) stack, device drivers, security manager, network stack, and more. Remarkably, KVM incorporates all these crucial components seamlessly into the Linux kernel itself. 

Consequently, each virtual machine within KVM is implemented as a regular Linux process, efficiently managed by the standard Linux scheduler. Furthermore, these VMs are equipped with dedicated virtual hardware, encompassing network cards, graphics adapters, CPUs, memory, and storage devices.

Implementing KVM

To put it concisely, in order to proceed, you’ll need to operate a Linux version that came out after 2007 and ensure it is installed on x86 hardware capable of virtualization. 

Once these prerequisites are met, the next steps involve loading two modules (a host kernel module and a processor-specific module), along with an emulator and any necessary drivers to facilitate the execution of additional systems.

Migrating to a KVM-based virtual infrastructure

When you construct a virtual infrastructure on a platform that imposes contractual limitations, it can impede your ability to access the source code. 

Consequently, your IT endeavors may be confined to workarounds rather than genuine innovations, and future contracts might hinder your investment in clouds, containers, and automation. 

However, by transitioning to a KVM-based virtualization platform, you gain the freedom to scrutinize, modify, and enhance the source code underlying your hypervisor. 

Moreover, there’s no need for an enterprise-license agreement since there is no source code to safeguard. It becomes entirely yours to shape and mold according to your needs.

KVM features

KVM and Linux share a symbiotic relationship, where they are interconnected and mutually beneficial. KVM is an integral component of the Linux ecosystem, inheriting all the robust features and capabilities that Linux offers. However, what sets KVM apart and makes it the hypervisor of choice for enterprises are its unique and distinctive features.

Security

KVM employs a powerful blend of security measures, leveraging the prowess of Security-Enhanced Linux (SELinux) and Secure Virtualization (sVirt) to fortify the security and isolation of virtual machines (VMs). SELinux plays a crucial role by establishing robust security boundaries around each VM, setting the stage for a resilient security framework. 

Building upon this foundation, sVirt extends the capabilities of SELinux, enabling the application of Mandatory Access Control (MAC) security to guest VMs. This added layer of protection safeguards against potential human errors in manual labeling, ensuring airtight security and peace of mind.

Storage

KVM boasts the flexibility of utilizing a wide array of storage options, taking advantage of the extensive storage support available in Linux. This includes leveraging local disks as well as network-attached storage (NAS). To enhance storage performance and ensure redundancy, KVM leverages Multipath I/O, which allows for improved I/O throughput and fault tolerance.

Furthermore, KVM extends its capabilities to support shared file systems, enabling multiple hosts to access and share VM images. This promotes efficient collaboration and resource utilization in virtualized environments.

When it comes to disk images, KVM offers the convenience of thin provisioning. This means that storage is allocated on-demand, rather than requiring upfront allocation of all storage space. This dynamic allocation ensures efficient resource utilization, enabling you to optimize your storage usage and avoid unnecessary overhead.

Hardware support

KVM boasts extensive compatibility with a diverse range of hardware platforms that have received certification for Linux support. This means that KVM can seamlessly utilize a wide array of hardware options, providing flexibility and choice to users.

One of the key reasons behind this compatibility is the active involvement of hardware vendors in kernel development. By contributing to the ongoing enhancement of the Linux kernel, these vendors ensure that the latest hardware features are swiftly integrated. As a result, KVM users can take advantage of cutting-edge advancements without delay.

The collaborative efforts between hardware vendors and the Linux community create a dynamic ecosystem where hardware innovations are rapidly adopted. This symbiotic relationship benefits both parties, as hardware vendors can showcase their latest technologies and users can leverage these advancements to enhance their virtualization experience.

Memory management

KVM leverages the memory management capabilities inherited from Linux, encompassing advanced functionalities such as non-uniform memory access (NUMA) and kernel same-page merging (KSM). By building upon these features, KVM ensures efficient and optimized memory utilization within virtual machines (VMs).

One notable aspect of memory management in KVM is the ability to swap VM memory. This enables the system to efficiently utilize large volumes of memory, resulting in improved performance and responsiveness. Additionally, KVM offers options for memory sharing, allowing multiple VMs to share common memory regions, further optimizing resource allocation.

Moreover, KVM provides the flexibility to back VM memory with disk storage. This approach allows for efficient utilization of disk space by allocating memory on demand, commonly known as overcommitment or thin provisioning. This dynamic allocation strategy optimizes resource usage while ensuring reliable performance for VMs.

By inheriting these powerful memory management features from Linux, KVM empowers users with robust and flexible memory configurations for their virtual environments. Whether it’s optimizing performance, sharing resources, or efficiently managing memory-backed disk storage, KVM provides the necessary tools to create a high-performance and scalable virtualization solution.

Live migration

KVM offers robust support for live migration, a feature that enables the seamless movement of a running virtual machine (VM) from one physical host to another without any interruption to services. This capability allows for the relocation of VMs while they are still powered on, ensuring that network connections remain active and applications continue to run uninterrupted during the migration process. 

During live migration, KVM captures and saves the current state of the VM, including its memory, processor context, and device configuration. This saved state is then transferred to the destination host, where the VM is resumed from the exact point it left off on the source host. By seamlessly transferring the VM’s state, KVM ensures that the migration is transparent to both the VM and its users, providing a smooth and uninterrupted experience.

Performance and scalability

KVM leverages the inherent performance capabilities of Linux, seamlessly scaling to accommodate increasing demand when the number of guest machines and incoming requests rises. 

This dynamic scalability ensures that KVM can efficiently handle even the most resource-intensive application workloads. 

As a result, KVM serves as the foundation for numerous enterprise virtualization deployments, including data centers and private clouds powered by OpenStack®.

Scheduling and resource control

In the KVM paradigm, a virtual machine (VM) is treated as a Linux process, effectively managed and scheduled by the underlying kernel. 

This unique approach leverages the advanced capabilities of the Linux scheduler, enabling precise control over resource allocation and ensuring a high level of service for each individual process. 

Within the realm of KVM, this encompasses a range of powerful features, including the completely fair scheduler, control groups, network name spaces, and real-time extensions.

Lower latency and higher prioritization

The Linux kernel incorporates specialized real-time extensions that enhance the performance of applications running in virtual machines (VMs), offering reduced latency and improved prioritization compared to running on bare metal. This feature enables VM-based applications to meet stringent timing requirements and deliver responsive performance.

To optimize the execution of processes with long computing times, the Linux kernel employs a technique called process segmentation. This involves dividing complex tasks into smaller components, known as threads or processes, which can be scheduled and processed independently. By breaking down these tasks, the kernel ensures that each component receives the necessary attention and computing resources, leading to efficient and effective processing.

Through the combination of real-time extensions and process segmentation, the Linux kernel enables VM-based applications to operate with lower latency, heightened prioritization, and enhanced efficiency. This empowers developers and system administrators to harness the full potential of virtualization while maintaining the performance required by demanding applications.

Managing KVM

Managing a few virtual machines (VMs) on a single workstation can be done manually without any specialized management tools. However, in large enterprise environments, the complexity and scale of virtualization necessitate the use of dedicated virtualization management software. These software solutions interfaces with the virtual environments and the underlying physical hardware to provide centralized control and streamline administrative tasks.

Virtualization management software offers a range of capabilities that simplify resource administration, enable comprehensive data analysis, and optimize operational efficiency. These tools provide a unified interface for managing multiple VMs, allowing administrators to monitor and allocate resources, configure network settings, and perform tasks such as creating, cloning, and migrating VMs.