x86/tsc_adjust.c

#include "libcflat.h"
#include "processor.h"

int main(void)
{
	u64 t1, t2, t3, t4, t5;
	u64 est_delta_time;

	if (this_cpu_has(X86_FEATURE_TSC_ADJUST)) { // MSR_IA32_TSC_ADJUST Feature is enabled?
		report("MSR_IA32_TSC_ADJUST msr initialization",
				rdmsr(MSR_IA32_TSC_ADJUST) == 0x0);
		t3 = 100000000000ull;
		t1 = rdtsc();
		wrmsr(MSR_IA32_TSC_ADJUST, t3);
		t2 = rdtsc();
		report("MSR_IA32_TSC_ADJUST msr read / write",
				rdmsr(MSR_IA32_TSC_ADJUST) == t3);
		report("TSC adjustment for MSR_IA32_TSC_ADJUST value",
				(t2 - t1) >= t3);
		t3 = 0x0;
		wrmsr(MSR_IA32_TSC_ADJUST, t3);
		report("MSR_IA32_TSC_ADJUST msr read / write",
				rdmsr(MSR_IA32_TSC_ADJUST) == t3);
		t4 = 100000000000ull;
		t1 = rdtsc();
		wrtsc(t4);
		t2 = rdtsc();
		t5 = rdmsr(MSR_IA32_TSC_ADJUST);
		// est of time between reading tsc and writing tsc,
		// (based on MSR_IA32_TSC_ADJUST msr value) should be small
		est_delta_time = t4 - t5 - t1;
		// arbitray 2x latency (wrtsc->rdtsc) threshold
		report("MSR_IA32_TSC_ADJUST msr adjustment on tsc write",
				est_delta_time <= (2 * (t2 - t4)));
	}
	else {
		report("MSR_IA32_TSC_ADJUST feature not enabled", true);
	}
	return report_summary();
}