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MSR Tools project provides utilities to access the processor MSRs and CPU ID directly.

This project is composed of three different user space console applications.

  • rdmsr – read MSR from any CPU or all CPUs
  • wrmsr – write values to MSR on any CPU or all CPUs
  • cpuid – show identification and feature information of any CPU

For more information, visit project website.

Disclaimer

Direct access to MSRs could harm a system. Because wrmsr requires root privilege, a root user could corrupt the system in any other ways. But a user is still recommended to be careful when writing values to MSRs. cpuid does not require any privilege to run and CPUID values are immutable.

Pre-requisite

To use '/dev/cpu/<cpu#>/msr' devices, 'msr' kernel module needs to be loaded. Do it by

$ modprobe msr

Similarly, to use '/dev/cpu/<cpu#>/cpuid' devices, 'cpuid' kernel module needs to be loaded. Do it by

$ modprobe cpuid

Build msr-tool

$ ./autogen.sh
$ make

Do the following if /dev/cpu DOES NOT EXIST on your system:

# create profile for each CPU core
$ ./MAKEDEV-cpuid-msr

Use msr-tool

Refer to tutorial here.

rdmsr / wrmsr

rdmsr / wrmsr give access to MSRs. Since it operates with '/dev/cpu/<cpu#>/msr' deivce, it requires a root privilege. And it can specify any CPU in a multi-processor system.

$ sudo rdmsr -p2 0x10

    => read the register value from Time Stamp Counter MSR 0x10 of CPU 2

cpuid

cpuid reads CPUID values from '/dev/cpu/<cpu#>/cpuid' device and shows a complete CPUID table for the specified processor. It should not require root access.

$ cpuid 3

	=> show all CPUID values of CPU 3