Updated April 14, 2023

Introduction to Linux KVM

KVM is defined as an open-source solution for enabling full virtualization of Linux on x86 hardware (initially built for x86 but later ported to S/390, PowerPC, IA-64, and ARM as well) that constitutes of extensions for virtualization. KVM is an acronym for Kernel-based Virtual Machine. This virtualisation setup contains a loadable kernel module named kvm.ko and a module-specific to the processor kvm-intel.ko or kvm-amd.ko. The selection between the processor-specific module is solely based on the type of processor hardware the machine is running on, either Intel or AMD. Also, the loadable kernel module provides infrastructure for core virtualization.

How does Linux KVM Work?

Before diving into that, one must be aware of the fact that even if there are multiple virtual machines running images, each of the virtual machines needs to have its own set of virtual private hardware, like network card, disk, graphics adapter, CPUs and many such more.
Now coming back to the point of working of KVM, Linux is converted into a Type-1 hypervisor. Now to see the working of KVM, we would be encountering a lot of new words or terminologies.+987poi Here, we will take care to explain each of those terminologies. A hypervisor is like a monitoring tool which creates virtual machines and monitors them. Using hypervisor allows one computer to run multiple VMs by monitoring and tracking the resource sharing like memory, processing etc. Now, once the Linux is converted into a hypervisor, all the system-level components, viz. memory manager, input-output stack, process scheduler, network stack, device drivers etc., are already in place as it is a part of Linux Kernel.
Post that every VM is implemented through a regular Linux process where the Linux scheduler schedules the implementation making sure all virtual hardware like network cards, graphics adapter etc., are in place. The hypervisor can be thought about as a layer which exists between the virtualized system and the real hardware. The isolated operating system views the hardware platform underlying as one belonging to it as the hypervisor creates a form of an illusion. As years passed by, the KVMs evolved as well. Now the CPU extensions are used for virtualization by using a module with the host operating system’s kernel. Also, in recent times, KVM uses paravirtualization for some input-output drives, which improves the performance of the system for certain use cases.

How to Use Linux KVM?

Before knowing how to install Linux KVM or running KVM in the system, it is mandatory to understand the virtualization capability of the processor or, in other words, understand if the processor can actually support hardware virtualization.

To check this, one must run the following command:

LC_ALL=C lscpu | grep Virtualization

grep -E --color=auto 'vmx|svm|0xc0f' /proc/cpuinfo

If one doesn’t obtain any result post running these command, it is for sure that the hardware doesn’t support virtualization. In those cases, we must first prepare the processor by upgrading or taking minor changes in the processor so that virtualization is possible. If the system is not ready for virtualization, one will not be able to use KVM.

Another thing which needs to be kept in mind is that one needs to run a version of Linux released after 2007. Once these 2 boxes are checked, the host kernel module and processor-specific modules are loaded, and following that virtualization, daemon libvirtd is restarted hence completing the install and deployment of KVM.

Once there, we can easily use KVM for spinning up a virtual machine using GNOME or GNOME Classic.

Advantages and Disadvantages of Linux KVM

Given below are the advantages and disadvantages of Linux KVM:

Advantages:

As the KVM system derives itself from Linux, it is quite a matured system.
KVM comes in-built in most of Linux distributions.
KVM is open source and hence free to use.
KVM ensures performance and stability.
It has been developed by reputable organizations hence making it trustworthy to be used.
Libvirt makes administration automated.

Disadvantages:

KVM is available only for Linux distributions.
The host computer needs to be powerful enough to take the load of multiple VMs.
Using KVM has a learning curve attached to it.
Since the hardware is centralized, hence the risk of losing data in case of system failure increases exponentially.

Features of Linux KVM

There are a lot of features available for KVM, majorly having 8 different genres to take care of, which makes it the obvious choice for enterprises’ favorite hypervisor.

1. Security

KVM uses a combination of security-enhanced Linux (SELinux) and secure virtualization (sVirt) for enhancing the VM security and isolation. Security boundaries are established around VMs and labels any manual labelling errors.

2. Storage

KVM also supports any storage supported by Linux as it belongs to the part of Linux only! KVM uses multipath I/O for removing redundancy and thus improving storage capability.

3. Hardware Support

A variety of Linux supported hardware is available by KVM, and since hardware vendors are major contributors to kernel development, it is rapidly adaptive in Linux Kernel.

4. Memory Management

The memory management features of Linux are inherited by KVM, making it even more up to date in terms of updates. Non-uniform memory access and kernel same-page merging are some of the KVM features, which are the latest in the market.

5. Live Migration

KVM as a solution enables the ability to perform live migration, which is very crucial in current times as the more decrease in down time of the system, the more effective the system is.

6. Performance and Scalability

With the inheritance capability from Linux, KVM easily scales up to match the demand load with the request for guest machines or request increase.

7. Scheduling and Resource Control

The Linux scheduler allows fine-grain control of the resource allocation to the KVM, making it super easy for one to control and schedule resources, enabling real-time extensions.

8. Lower Latency and Higher Prioritization

The real-time extension capability of Linux makes the VM based apps run at lower latency and hence adhering to better prioritization. Even a process requiring long computing times is broken into small components and then scheduled, run, and processed accordingly.

Conclusion

In this article, we have touched upon the important aspects of KVM. Now we know for sure that whenever there is a problem with non-flexibility or being unscalable, KVM will to rescue the developers at that time. Another feather in the hat of KVM is the capability of keeping the guest account lean and allowing them to use only for specific utilities only.

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