KVM is a virtualization technology that comes with the Linux kernel. In other words, it allows you to run multiple virtual machines (VMs) on a single Linux VM host. VMs in this case are known as guests. If you ever used QEMU or VirtualBox on Linux - you know what KVM is capable of.

But how does it work under the hood?

Also: https://lwn.net/Articles/658511/

source: trivium