This instruction must be run at privilege level 0 or in real-address mode; otherwise, a protection exception will be generated.
If less than 64 bits are implemented in a model specific register, the value returned to EDX:EAX, in the locations corresponding to the unimplemented bits, is unpredictable.
RDMSR is used to read the content of Model-Specific Registers that control functions for testability, execution tracing, performance monitoring and machine check errors. Refer to the Pentium(TM) Processor Data Book for more information.
The values 3H, 0FH, and values above 13H are reserved. Do not run RDMSR with reserved values in ECX.