Model Specific Registers
Processors from P6 family (including Pentium PRO, Pentium 3 & 4) have a collection of registers that allows configuration of various things such as memory type-range, sysenter/sysexit, local APIC, etc.
Accessing Model Specific Registers
Each MSR has a single 32-bit identification number that will be given to RDMSR or WRMSR assembly instructions to operate it. MSRs are 64-bit wide. The presence of MSRs on your processor is indicated by CPUID.01h:EDX[bit 5].
boolean cpuHasMSR()
{
dword a,d;
cpuid(1,&a,&d);
return d&CPUID_FLAG_MSR;
}
void cpuGetMSR(dword msr, dword *lo, dword *hi)
{
asm volatile("rdmsr":"=a"(*lo),"=d"(*hi):"c"(msr));
}
void cpuSetMSR(dword msr, dword lo, dword hi)
{
asm volatile("wrmsr"::"a"(lo),"d"(hi),"c"(msr));
}