rdmsr(9) - NetBSD Manual Pages

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RDMSR(9)             NetBSD/x86 Kernel Developer's Manual             RDMSR(9)


NAME

     msr, rdmsr, rdmsr_safe, wrmsr -- functions for x86 MSRs


SYNOPSIS

     #include <x86/cpufunc.h>

     uint64_t
     rdmsr(u_int msr);

     int
     rdmsr_safe(u_int msr, uint64_t *valp);

     void
     wrmsr(u_int msr, uint64_t val);


DESCRIPTION

     The RDMSR instruction reads from a x86 model-specific register (MSR).
     Conversely, the WRMSR instruction is used to write to a MSR.  In NetBSD
     the rdmsr(), rdmsr_safe(), and wrmsr() functions are used to access MSRs.
     The header <x86/specialreg.h> includes definitions for some of the com-
     monly used MSRs, that is, control registers that are present in some x86
     processor models but unavailable in others.


FUNCTIONS

     rdmsr(msr)
           Returns the value read from msr.

     rdmsr_safe(msr, valp)
           The rdmsr_safe() function is a safer variant of rdmsr().  Upon suc-
           cessful completion, the function returns zero and the value read
           from the register msr is returned in valp.  If a fault occurs while
           accessing msr, rdmsr_safe() returns EFAULT.

     wrmsr(msr, val)
           The wrmsr() function writes val to the register msr.

     Note that even though rdmsr_safe() provides support for reading MSRs in a
     safe manner, it is still a good practice to always verify that the given
     model-specific register is present by using the CPUID instruction, avail-
     able in NetBSD via x86_cpuid().


SEE ALSO

     rdtsc(9), x86/x86_msr_xcall(9)

NetBSD 10.0_STABLE             February 17, 2017            NetBSD 10.0_STABLE