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Higher-orderVirtualization

If `virtualization' is the process of building a virtual machine layer on top of a physical machine, then it makes sense for `higher-order virtualization' to be the process of building a virtual machine layer (guest VM) on top of another virtual machine (host VM).

This paradigm has several obvious benefits:

1. separation of concerns
2. abstraction of resource management
3. legacy code sandbox support

However, there are several concerns:

1. performance
2. communication between host and guest VMs

In fact, there is real tension between efficiency and VM layer isolation. A kind of paravirtualization? approach may be best, that exposes underlying host resources, but via a single, clean, manageable API, like the VM_Magic API in JikesRVM.

There could be some synergy between virtualization and parallelization. Both trends are increasing for workstation-class machines at present. The extra parallel resources could be used to "soak up" the inefficiencies of higher-order virtualization.