Q. Does Hyper-V in Windows Server 2008 R2 take advantage of the Nested Page Tables and Extended Page Tables features in the latest AMD and Intel processors?

A. Yes. Recent AMD and Intel processors add support for Nested Page Tables and Extended Page Tables respectively. These features essentially make it so that the Virtual Machine Manager (VMM) in the hypervisor layer no longer has to maintain mapping tables of guest memory to physical memory (Shadow Page Tables). This mapping is one of the biggest overheads of the hypervisor. Each virtual machine (VM) has its own map of memory that is unlikely to map to the physical pages of memory on the server, so every time a VM references a page, the VMM has to do translate the virtual memory address to the physical memory address. This translation is expensive in CPU power for the VMM.

With the Nested Page Tables and Extended Page Tables features, the processor maintains page tables for the guest VMs, so the VMM no longer has to do this translation, reducing the work of the hypervisor and improving performance. Hyper-V 2008 R2 automatically checks for Nested Page Tables and Extended Page Tables in the processor and uses the features if available. No configuration is necessary.

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