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RDMSR

Reads a model-specific register (MSR) specified by the value in the ECX register into EDX:EAX.

The table below covers what the source and destinations can be.

DO NOT support LOCK

This instruction SHALL only be executed at privilege level 0 (CPL=0). Execution at any other privilege level SHALL result in a general-protection exception (#GP(0)).

The value of the MSR is loaded into EDX:EAX; if the MSR is smaller than 64 bits, the upper bits of EDX SHALL be cleared. Attempting to read an undefined MSR SHALL result in a general-protection exception (#GP(0)).

To avoid #GP(0) exceptions, the software MUST verify the processor's supported MSRs via CPUID or by referring to the specific processor's architectural documentation before execution.