Virtualization Without Direct Execution or Jitting: Designing a Portable Virtual Machine Infrastructure

A recent trend in x86 virtualization products from Microsoft, VMware, and XenSource has been the reliance on hardware virtualization features found in current 64-bit microprocessors. Hardware virtualization allows for direct execution of guest code and potentially simplifies the implementation of a Virtual Machine Monitor (or "Hypervisor"). Until recently, hypervisors on the PC platform have relied on a variety of techniques ranging from the slow but simple approach of pure interpretation, the memory intensive approach of dynamic recompilation of guest code into translated code cache, to a hardware assisted technique known as "Ring compression" which relies on the host MMU for hardware memory protection. These techniques traditionally either deliver poor performance, or are not portable.