VMware 4817V62 - vSphere - PC Administration Manual page 187

Chapter 16 Migrating Virtual Machines
CPU Families and Feature Sets
Processors are grouped into families. Processors within a given family generally have similar feature sets.
Processor families are defined by the processor vendors. You can distinguish different processor versions
within the same family by comparing the processors' model, stepping level, and extended features. In some
cases, processor vendors have introduced significant architectural changes within the same processor family,
such as the SSSE3 and SSE4.1 instructions, and NX/XD CPU security features.
By default, vCenter Server identifies mismatches on features accessible to applications as incompatible to
guarantee the stability of virtual machines after migrations with VMotion.
Server hardware's CPU specifications will usually indicate whether or not the CPUs contain the features that
affect VMotion compatibility. If the specifications of a server or its CPU features are unknown, VMware's
bootable CPU identification utility (available for download from the VMware website) can be used to boot a
server and determine whether its CPUs contain features such as SSE3, SSSE3, and NX/XD.
®
For more information on identifying Intel processors and their features, see Application Note 485: Intel Processor
Identification and the CPUID Instruction, available from Intel. For more information on identifying AMD
processors and their features, see CPUID Specification, available from AMD.
NX/XD Considerations
The AMD No eXecute (NX) and the Intel eXecute Disable (XD) technology serve the same security purpose.
They mark memory pages as data-only to prevent malicious software exploits and buffer overflow attacks.
Refer to the documentation for your guest operating system to determine whether it supports NX and XD.
In ESX/ESXi 3.0 and later, NX and XD technology is exposed by default for all guest operating systems that
can use it (trading off some compatibility for security by default). Hosts that were previously compatible for
VMotion in ESX Server 2.x might become incompatible after upgrading to ESX/ESXi 3.0 and later, because the
NX or XD is now exposed when it was previously suppressed, but you can use per-virtual machine CPU
compatibility masks to restore compatibility.
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