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.

If you think about it, this is probably the very reason most of the KVM internals were already in the Linux Kernel when Xen and VmWare were arguing over the "standard" for the changes to the Linux Kernel they needed. It pretty obvious that this is the reason why to me. The changes are straightforward and simple.