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40 Datasheet, Volume 1
3.1.2 Intel
®
Virtualization Technology (Intel
®
VT) for
IA-32, Intel
®
64 and Intel
®
Architecture
(Intel
®
VT-x) Features
The processor core supports the following Intel VT-x features:
• Extended Page Tables (EPT)
— EPT is hardware assisted page table virtualization
— It eliminates VM exits from guest operating system to the VMM for shadow
page-table maintenance
• Virtual Processor IDs (VPID)
— Ability to assign a VM ID to tag processor core hardware structures (such as
TLBs)
— This avoids flushes on VM transitions to give a lower-cost VM transition time
and an overall reduction in virtualization overhead
• Guest Preemption Timer
— Mechanism for a VMM to preempt the execution of a guest operating system
after an amount of time specified by the VMM. The VMM sets a timer value
before entering a guest.
— The feature aids VMM developers in flexibility and Quality of Service (QoS)
guarantees
• Descriptor-Table Exiting
— Descriptor-table exiting allows a VMM to protect a guest operating system from
internal (malicious software based) attack by preventing relocation of key
system data structures like IDT (interrupt descriptor table), GDT (global
descriptor table), LDT (local descriptor table), and TSS (task segment selector)
— A VMM using this feature can intercept (by a VM exit) attempts to relocate
these data structures and prevent them from being tampered by malicious
software
3.1.3 Intel
®
Virtualization Technology (Intel
®
VT) for Directed
I/O (Intel
®
VT-d) Objectives
The key Intel VT-d objectives are domain-based isolation and hardware-based
virtualization. A domain can be abstractly defined as an isolated environment in a
platform to which a subset of host physical memory is allocated. Virtualization allows
for the creation of one or more partitions on a single system. This could be multiple
partitions in the same operating system, or there can be multiple operating system
instances running on the same system – offering benefits such as system
consolidation, legacy migration, activity partitioning, or security.