Are Virtual Machine Monitors Microkernels Done Right?

What Kind of Paper?

• Position
• Response to other paper of the same name
• Claim the other paper is erroneous, and this paper corrects it

Definitions

• VMM: "software which transforms the single machine interface into the illusion of many."
• Microkernel: "to minimize the kernel and to implement whatever possible outside of the kernel"

Goals (similarity)

• VMM: software reliability, data security, alternative system APIs, improved and new mechanisms
• Microkernel: flexibility, extensibility, fault isolation, maintainability, and restricted interdependencies.

Revisiting Hand's Assertions

• Liability Inversion
  • Claim Xen suffers from identical problem.
  • Both cite Parallax as example to prove their point.
  • Hand says that Parallax only affects other VMs
  • Heiser says that this is the same as a failure of an L4 server
• IPC Performance
  • Xen uses Dom0 for drivers, so all I/O requires IPC (simple asynchronous unidirectional event mechanism) with Dom0
  • CPU load of Dom0 dominates all other CPU load, so it *is* performance critical.
• VMMs provide familiar environment
  • L4 Linux was presented many years ago, apparently satisfying the same criteria.