KVM for Beginners – Kernel-based Virtual Machine: An Introduction – Part 1

There is no question that many are looking at virtualization alternatives in 2024 and beyond, with the major shakeups happening across the industry in general. With the recent Broadcom changes, many organizations are looking at alternative hypervisors to VMware vSphere. Many hypervisors based on Kernel Virtual Machine (KVM) provide great platforms for running business-critical virtual machines and containers. Let’s look at options for KVM solutions in the enterprise.

What is Kernel-based Virtual Machine (KVM)

First of all, let’s explore what the KVM hypervisor is exactly. Kernel Virtual Machine is a Linux-based technology found in the Linux kernel that allows it to function as a hypervisor to run virtualization infrastructure.

This feature was introduced in the Linux kernel in 2007 and found in most Linux distros, including Red Hat Enterprise Linux and many enterprise virtualization setups. Using KVM, you can run multiple virtual machines with guest operating systems using hardware virtualization.

The KVM host kernel module in the Linux kernel mainline is called kvm.ko and works with hardware virtualization extensions built into modern processors like Intel VT-x or AMD AMD-V as a virtualization solution. It allows KVM to have the performance needed by using the processor’s features directly.

QEMU is a standard userspace tool that can be used as a machine emulator and virtualization manager to manage virtual hardware and networking.

Supported features

Note the following list of supported features with Kernel Virtual Machine:

• QMP: QEMU Monitor Protocol, used for interacting with QEMU instances
• KSM: Kernel Samepage Merging, a memory-saving de-duplication feature
• KVM Paravirtual Clock: A paravirtual time source for KVM, enhancing time accuracy in virtual machines
• CPU Hotplug Support: Capability to dynamically add CPUs to a running system
• PCI Hotplug Support: Capability to dynamically add PCI devices to a system while it’s running
• vmchannel: A communication channel between the host and its guest virtual machines
• Migration: Process of moving virtual machines from one host to another
• Nested Guests: The ability to run virtual machines within other virtual machines
• vhost: A mechanism to accelerate guest networking by delegating data plane operations to the host kernel
• SCSI Disk Emulation: Simulates SCSI disk drives in a virtual environment
• Virtio Devices: Provides efficient I/O virtualization for virtual machines
• CPU Clustering: Groups multiple CPUs for more efficient processing in virtual environments
• HPET (High Precision Event Timer): Provides high-precision timers to virtual machines
• Device Assignment: Allocates physical devices to specific virtual machines
• PXE Boot: Boots virtual machines using the network, following the PXE standard
• iSCSI Boot: Allows virtual machines to boot from remote iSCSI storage devices
• x2APIC: Extended APIC support for more scalable interrupt management in virtual machines
• Floppy Disk Emulation: Simulates floppy drives for virtual machines
• CDROM Emulation: Allows virtual machines to read from virtual CD-ROM drives
• USB Emulation: Simulates USB devices within virtual machines
• USB Host Device Passthrough: Allows direct access to USB devices from within virtual machines
• Sound Emulation: Provides sound capabilities to virtual machines
• Sound Emulation: Emulates IRQ chips in user space for virtual machines
• Userspace PIT Emulation: Emulates Programmable Interval Timers in user space for enhanced timing in virtual machines
• Balloon Memory Driver: Dynamically adjusts the memory allocation of guest virtual machines
• Large Pages Support: Enhances performance by using larger memory pages
• Stable Guest ABI: Ensures a consistent application binary interface within guest virtual machines for compatibility and stability

KVM virtualization solutions

Since KVM is built natively into Linux, many free and open-source solutions build their virtualization solutions around Kernel Virtual Machines. One hypervisor built on top of KVM that has been gaining a lot of traction in the home lab community, the SMB space, and even the enterprise is Proxmox.

Not only does Proxmox integrate KVM as the hypervisor, but it also runs Linux Containers (LXC) and provides software-defined networking functionality. Along with an easy-to-use interface, it also has built-in clustering, is highly available, and is a backup solution that can be downloaded and used at no cost.

For businesses and organizations that need enterprise support, Proxmox has paid support options for mission-critical environments.

Note the following storage and networking capabilities with Proxmox:

• LVM, LVM-thin, iSCSI, Ceph/RBD, ZFS over iSCSI, ZFS (local), directory, NFS, CIFS, GlusterFS, Proxmox Backup Server, ESXi storage mounting for new migration wizard
• Bridged-Networking along with virtualized networking, with Open vSwitch

Nutanix is well-known in the enterprise space as a paid solution for virtualization. It is also built around a heavily modified version of KVM that provides a mainstream commercial solution for organizations looking for a VMware alternative enterprise platform.

It is designed as a purpose-built hyper-converged infrastructure (HCI) solution that provides software-defined storage on which to run production workloads.

Key features of Nutanix virtualization based on KVM include:

• AHV Hypervisor: Nutanix’s Acropolis Hypervisor (AHV) is built on KVM
• Scalability: Nutanix uses KVM capabilities to scale environments as needed
• Security KVM: It provides robust security features. These include data-at-rest encryption and strong isolation of virtual machines
• Integrated Virtual Networking: It allows configuring virtual switches, and network function virtualization allows for sophisticated network configurations within the virtual environment
• Management: It provides centralized management using Nutanix’s Prism interface. It provides a single control point for managing Nutanix’s virtual infrastructure
• Snapshot and DR Capabilities: Nutanix has a solution for HA, disaster recovery, and snapshot capabilities

Nutanix also offers a free Nutanix Community Edition (CE) that allows admins to get their hands on KVM virtualization with Nutanix. It is free to download and can be set up and installed on consumer-grade hardware. Below is a screenshot of Nutanix Community Edition installed on home lab hardware.

Wrapping up

Kernel Virtual Machine (KVM) is an excellent platform for virtualizing workloads, including virtual machines and containers and is included as a Linux kernel module since 2007. Many great Linux KVM solutions are even free and open-source. Proxmox VE Server is gaining popularity in the community and in SMB environments, with many transitioning from VMware ESXi with the recent Broadcom shakeup. KVM is also at the heart of other enterprise solutions like Nutanix. Nutanix is one of the well-known enterprise virtualization setups and even offers a free Nutanix Community Edition to allow admins to access Nutanix virtualization and become familiar with the solution.

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