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80 Intel® Xeon® Processor E5-1600/E5-2600/E5-4600 Product Families
Datasheet Volume One
3.1.2 Intel VT-x Features
The processor core supports the following Intel VT-x features:
• Extended Page Tables (EPT)
— hardware assisted page table virtualization
— eliminates VM exits from guest OS to the VMM for shadow page-table
maintenance
• Virtual Processor IDs (VPID)
— Ability to assign a VM ID to tag processor core hardware structures (for
example, 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 OS 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 OS 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.
• Pause Loop Exiting (PLE)
— PLE aims to improve virtualization performance and enhance the scaling of
virtual machines with multiple virtual processors
— PLE attempts to detect lock-holder preemption in a VM and helps the VMM to
make better scheduling decisions
3.1.3 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.
3.1.3.1 Intel VT-d Features Supported
The processor supports the following Intel VT-d features:
• Root entry, context entry, and default context
• Support for 4-K page sizes only
• Support for register-based fault recording only (for single entry only) and support
for MSI interrupts for faults