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System

USER_MSR

Lets user-mode code read and write the model-specific registers that the operating system allows in a bitmap.

CPUID
USER_MSR
CPUID.(EAX=07H,ECX=1):EDX[15]
Instructions
2 mnemonics
Processors
Clearwater Forest

URDMSR and UWRMSR let user-mode code read and write model-specific registers that the operating system has chosen to expose. The kernel enables them and points the IA32_USER_MSR_CTL MSR at a 4-KiB bitmap: its low half has one bit per MSR address from 0 to 3FFFH for URDMSR, its high half the same for UWRMSR, and any access without its bit set raises #GP. The SDM currently names IA32_UARCH_MISC_CTL as the only MSR UWRMSR may write. Both instructions exist only in 64-bit mode, with the address in a register or an immediate. Intel lists Clearwater Forest as the first processor with them.

Instructions

Mnemonics with at least one form in USER_MSR. Each page lists all forms of the mnemonic, including those of other extensions.
MnemonicSummaryForms
URDMSRReads a model-specific register from user mode, if the operating system allows that register in its user-MSR bitmap.2
UWRMSRWrites a model-specific register from user mode, if the operating system allows that register in its user-MSR bitmap.2

CPUID and processors

XED splits USER_MSR into 1 ISA set. Software can use a form when the processor reports every CPUID bit of one alternative of the form's ISA set.

XED ISA sets of USER_MSR. Alternatives are separated by “or”; processors follow XED’s chip model, which covers AMD processors up to Zen 2.
ISA setCPUIDProcessors in XED
USER_MSR

USER_MSR
CPUID.(EAX=07H,ECX=1):EDX[15] USER_MSR

Clearwater Forest

Sources

  1. Intel XED v2026.08.23 (commit 0bcb6237345c): forms, encodings, ISA sets, CPUID bits and chip model.
  2. Intel 64 and IA-32 Architectures Software Developer's Manual, Volume 2 (325383-092, June 2026)
  3. Intel Architecture Instruction Set Extensions and Future Features Programming Reference (319433-062, June 2026)

The tables are derived from Intel XED, Copyright Intel Corporation, licensed under the Apache License 2.0; x86-64.net converted and reformatted them. The text is our own.