Yeah I also found myself curious as to how KVM actually works, I found these helpful
https://www.kernel.org/doc/ols/2007/ols2007v1-pages-225-230.... http://www.haifux.org/lectures/312/High-Level%20Introduction... https://zserge.com/posts/kvm/
https://www.kernel.org/doc/ols/2007/ols2007v1-pages-225-230.... http://www.haifux.org/lectures/312/High-Level%20Introduction... https://zserge.com/posts/kvm/
My rough understanding is that it's the user-space emulation part of a virtualization solution. I.e., when the kernel traps the virtualized process, saying 'nope, you can't do that here', the control falls back to user space handler in QEMU saying, 'hey, the kernel said I can't do that there; can you sort this out?'. And this back-and-forth games keeps happening during the lifetime of the virtualized process.