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Which processors support MONITOR/MWAIT at CPL > 0

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Which processors support MONITOR/MWAIT at CPL > 0? Is that information documented anywhere? More specifically, on Linux is there something special that needs to be done to enable MONITOR/MWAIT at user privilege level? An application on Linux reports CPUID(1).ecx[3] == 1 on Nehalem (Xeon X5570 Dell r610) yet MONITOR/MWAIT result in # UD exception. Documentation on this is ambiguous.

http://www.intel.com/Assets/PDF/manual/253668.pdf http://www.intel.com/Assets/PDF/manual/253668.pdf

Intel® 64 and IA-32 Architectures

 

Software Developer's Manual

 

Volume 3A: System Programming Guide, Part 1

Order Number: 253668-033US

 

December 2009

14.4 MWAIT EXTENSIONS FOR ADVANCED POWER

 

MANAGEMENT

Page 14-10 Vol. 3

Says

At CPL=0, system software can specify desired C-state and sub C-state by using the

 

MWAIT hints register (EAX). Processors will not go to C-state and sub C-state deeper

 

than what is specified by the hint register. If CPL>0 and if MONITOR/MWAIT is

 

supported at CPL>0, the processor will only enter C1-state (regardless of the

 

C-state request in the hints register).

 

Executing MWAIT generates an exception on processors operating at a privilege level

 

where MONITOR/MWAIT are not supported.

Thanks.

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