Using the KVM API

Well if you look at what KVM does... all it ultimately does is allow you to execute ring0 code in ring2 on a x86 cpu. That way you don't have to modify the OS kernel to be able to execute it as a application. The alternative is to do what Xen did with Linux and patch it so that you can run the Linux kernel more like a regular application.

Previously you had kernel mode and then you had usermode ways to execute code. Now you have a third way, the kvm way. There isn't much to emulate because it's not using emulation at all. It's just executing the code directly on your processor. The only really magic/complicated stuff that happens is to deal with memory addressing for the guest OS.

Qemu does all the heavy lifting as far as 'system emulator' goes.