KVM (Kernel Virtual Machine) is a Linux kernel module that allows a user space program to utilize the hardware virtualization features of various processors. Support for KVM for Arm dates back to work in the 3.9 kernel in 2013 from Christoffer Dall and Jason Nieh. A detailed writeup, Supporting KVM on the ARM architecture, was published to LWN.
KVM support is built into modern Linux kernels; there is nothing additional to install or load. QEMU can make use of KVM when running a target architecture that is the same as the host architecture to speed up virtualization.