Your second paragraph is exactly what I meant by adding hardware emulation code to create a less efficient and uglier API. The hardware-like interface to the h

Your second paragraph is exactly what I meant by adding hardware emulation code to create a less efficient and uglier API. The hardware-like interface to the hypervisor is both inefficient and not very abstract. For instance, a guest kernel attempts to perform a series of manipulations of the page table, each of which traps to the hypervisor, or else it performs an equivalent upcall to manipulate the page tables. The hardware emulation code ads a lot of potential bugs to the hypervisor. I hope our current hypervisors are an evolutionary transitional form and in the future we'll interact with hypervisors solely through upcalls.