/*
 * VM exit benchmark using a hypercall
 *
 * Copyright (c) Siemens AG, 2015
 *
 * Authors:
 *  Jan Kiszka <jan.kiszka@siemens.com>
 *
 * This work is licensed under the terms of the GNU GPL, version 2.  See
 * the COPYING file in the top-level directory.
 */

#ifndef __x86_64__
#error only x86-64 supported
#endif

#include <stdbool.h>
#include <stdio.h>

#define LOOPS			1000000

#define X86_FEATURE_VMX		(1UL << 5)

static inline unsigned long cpuid_ecx(void)
{
	unsigned long val;

	asm volatile("cpuid" : "=c" (val) : "a" (1) : "ebx", "edx");
	return val;
}

static inline __attribute__((always_inline)) unsigned long long read_tsc(void)
{
	unsigned long long hi, lo;

	asm volatile("rdtsc" : "=a" (lo), "=d" (hi));
	return (hi << 32) | lo;
}

int main(int argc, char *argv[])
{
	bool use_vmcall = !!(cpuid_ecx() & X86_FEATURE_VMX);
	unsigned long long start, sum = 0;
	unsigned int n;

	for (n = 0; n < LOOPS; n++) {
		if (use_vmcall) {
			start = read_tsc();
			asm volatile("vmcall" : : "a" (-1));
			sum += read_tsc() - start;
		} else {
			start = read_tsc();
			asm volatile("vmmcall" : : "a" (-1));
			sum += read_tsc() - start;
		}
	}
	printf("Null hypercall: %llu cycles\n", sum / LOOPS);

	return 0;
}