Intel VT Virtualization Architecture Highlights

Intel Virtualization Technology (Intel VT) provides a processor architecture that supports virtualization software applications through a set of extensions referred to as Virtual Machine Extensions (VMX). Here are Intel VT VMX highlights commonly mentioned with reference to virtualization software:

• VMX Root operating mode - allows a hypervisor or VMM to execute in fully privileged mode.
• VMX Non-Root operating mode - allows a guest operating system to execute in Ring 0 and the application stack in Ring 3.
• Ten VMX instructions - support virtualization, including VMLAUNCH which enables the context switch to load and execute a new guest operating system.
• Virtual Memory Control Data Structure (VMCS) - contains guest and host state information, as well as VMX control fields used to manage the transitions between VMX Root and VMX Non-Root operating modes.
• Virtual Processor Identifier (VPID) - a unique identifier assignment stored in the VMCS to distinguish between co-existing host and guest entries. TLB entries are tagged with the appropriate VPID value, reducing the impact during context switches by not requiring a flush and reload of the TLB.
• Simultaneous support for 16-bit, 32-bit, and 64-bit guest operating systems.
• Extended Page Tables (EPT) - provide processor-powered translation of the guest physical memory address space to the host physical address space.

Like in the case of AMD-V Rapid Virtualization Indexing, Hyper-V does not leverage the Intel VT Extended Page Tables features in the initial release. Bottom line, Intel VT and AMD-V architectures offer much similar functionality to virtualization software application developers, although their feature implementation, nomenclature, and performance may differ from each other.

Here is a reference document from Intel on this topic: http://softwarecommunity.intel.com/isn/downloads/virtualization.pdf.

You can also get more detailed information on the Intel VT from the Intel 64 and IA-32 Architectures Software Developer's Manuals at http://www.intel.com/products/processor/manuals/.