With the EFI stub in the Linux kernel and the ability to embed an initrd in the kernel, you can boot a small distribution with just the kernel file. The only is

With the EFI stub in the Linux kernel and the ability to embed an initrd in the kernel, you can boot a small distribution with just the kernel file. The only issue is that it takes a long time to load a very large kernel into memory like that. I tried that with a buildroot based hypervisor I created for my home lab.