libhermit/arch/x86/kernel/processor.c

/*
 * Copyright (c) 2010, Stefan Lankes, RWTH Aachen University
 * All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions are met:
 *    * Redistributions of source code must retain the above copyright
 *      notice, this list of conditions and the following disclaimer.
 *    * Redistributions in binary form must reproduce the above copyright
 *      notice, this list of conditions and the following disclaimer in the
 *      documentation and/or other materials provided with the distribution.
 *    * Neither the name of the University nor the names of its contributors
 *      may be used to endorse or promote products derived from this
 *      software without specific prior written permission.
 *
 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS" AND
 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED
 * WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
 * DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE FOR ANY
 * DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES
 * (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
 * LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND
 * ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
 * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS
 * SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 */

#include <hermit/stddef.h>
#include <hermit/stdio.h>
#include <hermit/string.h>
#include <hermit/time.h>
#include <hermit/processor.h>
#include <hermit/tasks.h>
#include <hermit/logging.h>
#include <asm/multiboot.h>

/*
 * Note that linker symbols are not variables, they have no memory allocated for
 * maintaining a value, rather their address is their value.
 */
extern const void percore_start;
extern const void percore_end0;
extern const void percore_end;
extern void* Lpatch0;
extern void* Lpatch1;
extern void* Lpatch2;
extern atomic_int32_t current_boot_id;

extern void isrsyscall(void);

cpu_info_t cpu_info = { 0, 0, 0, 0, 0};
static char cpu_vendor[13] = {[0 ... 12] = 0};
static char cpu_brand[4*3*sizeof(uint32_t)+1] = {[0 ... 4*3*sizeof(uint32_t)] = 0};
extern uint32_t cpu_freq;

static void default_save_fpu_state(union fpu_state* state)
{
	asm volatile ("fnsave %0; fwait" : "=m"((*state).fsave) :: "memory");
}

static void default_restore_fpu_state(union fpu_state* state)
{
	asm volatile ("frstor %0" :: "m"(state->fsave));
}

static void default_fpu_init(union fpu_state* fpu)
{
	i387_fsave_t *fp = &fpu->fsave;

	memset(fp, 0x00, sizeof(i387_fsave_t));
	fp->cwd = 0xffff037fu;
	fp->swd = 0xffff0000u;
	fp->twd = 0xffffffffu;
	fp->fos = 0xffff0000u;
}

static void default_writefs(size_t fs)
{
	wrmsr(MSR_FS_BASE, fs);
}

static size_t default_readfs(void)
{
	return rdmsr(MSR_FS_BASE);
}

static void default_writegs(size_t gs)
{
	wrmsr(MSR_GS_BASE, gs);
}

static size_t default_readgs(void)
{
	return rdmsr(MSR_GS_BASE);
}

static void wrfsbase(size_t fs)
{
	asm volatile ("wrfsbase %0" :: "r"(fs));
}

static size_t rdfsbase(void)
{
	size_t ret = 0;

	asm volatile ("rdfsbase %0" : "=r"(ret) :: "memory");

	return ret;
}

static void wrgsbase(size_t gs)
{
	asm volatile ("wrgsbase %0" :: "r"(gs));
}

static size_t rdgsbase(void)
{
	size_t ret = 0;

	asm volatile ("rdgsbase %0" : "=r"(ret) :: "memory");

	return ret;
}

func_read_fsgs readfs = default_readfs;
func_read_fsgs readgs = default_readgs;
func_write_fsgs writefs = default_writefs;
func_write_fsgs writegs = default_writegs;

handle_fpu_state save_fpu_state = default_save_fpu_state;
handle_fpu_state restore_fpu_state = default_restore_fpu_state;
handle_fpu_state fpu_init = default_fpu_init;

static void save_fpu_state_fxsr(union fpu_state* state)
{
	asm volatile ("fxsave %0; fnclex" : "=m"(state->fxsave) :: "memory");
}

static void restore_fpu_state_fxsr(union fpu_state* state)
{
	asm volatile ("fxrstor %0" :: "m"(state->fxsave));
}

static void fpu_init_fxsr(union fpu_state* fpu)
{
	i387_fxsave_t* fx = &fpu->fxsave;

	memset(fx, 0x00, sizeof(i387_fxsave_t));
	fx->cwd = 0x37f;
	if (BUILTIN_EXPECT(has_sse(), 1))
		fx->mxcsr = 0x1f80;
}

static void save_fpu_state_xsave(union fpu_state* state)
{
	asm volatile ("xsaveq %0" : "=m"(state->xsave) : "a"(-1), "d"(-1) : "memory");
}

static void restore_fpu_state_xsave(union fpu_state* state)
{
	asm volatile ("xrstorq %0" :: "m"(state->xsave), "a"(-1), "d"(-1));
}

static void fpu_init_xsave(union fpu_state* fpu)
{
	xsave_t* xs = &fpu->xsave;

	memset(xs, 0x00, sizeof(xsave_t));
	xs->fxsave.cwd = 0x37f;
	xs->fxsave.mxcsr = 0x1f80;
}

static uint32_t get_frequency_from_mbinfo(void)
{
	if (mb_info && (mb_info->flags & MULTIBOOT_INFO_CMDLINE) && (cmdline))
	{
		// search in the command line for cpu frequency
		char* found = strstr((char*) (size_t)cmdline, "-freq");
		if (!found)
			return 0;

		return atoi(found+strlen("-freq"));
	}

	return 0;
}

// Try to determine the frequency from the CPU brand.
// Code is derived from the manual "Intel Processor
// Identification and the CPUID Instruction".
static uint32_t get_frequency_from_brand(void)
{
	uint32_t index, multiplier = 0;

	for(index=0; index<sizeof(cpu_brand)-2; index++)
	{
		if ((cpu_brand[index+1] == 'H') && (cpu_brand[index+2] == 'z'))
		{
			if (cpu_brand[index] == 'M')
				multiplier = 1;
			else if (cpu_brand[index] == 'G')
				multiplier = 1000;
			else if (cpu_brand[index] == 'T')
				multiplier = 1000000;
		}

		if (multiplier > 0) {
			uint32_t freq;

			// Compute frequency (in MHz) from brand string
			if (cpu_brand[index-3] == '.') { // If format is “x.xx”
				freq  = (uint32_t)(cpu_brand[index-4] - '0') * multiplier;
				freq += (uint32_t)(cpu_brand[index-2] - '0') * (multiplier / 10);
				freq += (uint32_t)(cpu_brand[index-1] - '0') * (multiplier / 100);
			} else { // If format is xxxx
				freq  = (uint32_t)(cpu_brand[index-4] - '0') * 1000;
				freq += (uint32_t)(cpu_brand[index-3] - '0') * 100;
				freq += (uint32_t)(cpu_brand[index-2] - '0') * 10;
				freq += (uint32_t)(cpu_brand[index-1] - '0');
				freq *= multiplier;
			}

			return freq;
		}
	}

	return 0;
}

uint32_t detect_cpu_frequency(void)
{
	uint64_t start, end, diff;
	uint64_t ticks, old;

	if (BUILTIN_EXPECT(cpu_freq > 0, 0))
		return cpu_freq;

	cpu_freq = get_frequency_from_mbinfo();
	if (cpu_freq > 0)
		return cpu_freq;
	cpu_freq = get_frequency_from_brand();
	if (cpu_freq > 0)
		return cpu_freq;

	old = get_clock_tick();

	/* wait for the next time slice */
	while((ticks = get_clock_tick()) - old == 0)
		PAUSE;

	rmb();
	start = rdtsc();
	/* wait 3 ticks to determine the frequency */
	while(get_clock_tick() - ticks < 3)
		PAUSE;
	rmb();
	end = rdtsc();

	diff = end > start ? end - start : start - end;
	cpu_freq = (uint32_t) ((TIMER_FREQ*diff) / (1000000ULL*3ULL));

	return cpu_freq;
}

static int get_min_pstate(void)
{
	uint64_t value;

	value = rdmsr(MSR_PLATFORM_INFO);

	return (value >> 40) & 0xFF;
}

static int get_max_pstate(void)
{
	uint64_t value;

	value = rdmsr(MSR_PLATFORM_INFO);

	return (value >> 8) & 0xFF;
}

static uint8_t is_turbo = 0;
static int max_pstate, min_pstate;
static int turbo_pstate;

static int get_turbo_pstate(void)
{
	uint64_t value;
	int i, ret;

	value = rdmsr(MSR_NHM_TURBO_RATIO_LIMIT);
	i = get_max_pstate();
	ret = (value) & 255;
	if (ret < i)
		ret = i;

	return ret;
}

static void set_pstate(int pstate)
{
	uint64_t v = pstate << 8;
	if (is_turbo)
		v |= (1ULL << 32);
	wrmsr(MSR_IA32_PERF_CTL, v);
}

void dump_pstate(void)
{
	if (!has_est())
		return;

	LOG_INFO("P-State 0x%x - 0x%x, turbo 0x%x\n", min_pstate, max_pstate, turbo_pstate);
	LOG_INFO("PERF CTL 0x%llx\n", rdmsr(MSR_IA32_PERF_CTL));
	LOG_INFO("PERF STATUS 0x%llx\n", rdmsr(MSR_IA32_PERF_STATUS));
}

static void check_est(uint8_t out)
{
	uint32_t a=0, b=0, c=0, d=0;
	uint64_t v;

	if (!has_est())
		return;

	if (out)
		LOG_INFO("System supports Enhanced SpeedStep Technology\n");

	// enable Enhanced SpeedStep Technology
	v = rdmsr(MSR_IA32_MISC_ENABLE);
	if (!(v & MSR_IA32_MISC_ENABLE_ENHANCED_SPEEDSTEP)) {
		if (out)
			LOG_INFO("Linux doesn't enable Enhanced SpeedStep Technology\n");
		return;
	}

	if (v & MSR_IA32_MISC_ENABLE_SPEEDSTEP_LOCK) {
		if (out)
			LOG_INFO("Enhanced SpeedStep Technology is locked\n");
		return;
	}

	if (v & MSR_IA32_MISC_ENABLE_TURBO_DISABLE) {
		if (out)
			LOG_INFO("Turbo Mode is disabled\n");
	} else {
		if (out)
			LOG_INFO("Turbo Mode is enabled\n");
		is_turbo=1;
	}

	cpuid(6, &a, &b, &c, &d);
	if (c & CPU_FEATURE_IDA) {
		if (out)
			LOG_INFO("Found P-State hardware coordination feedback capability bit\n");
	}

	if (c & CPU_FEATURE_HWP) {
		if (out)
			LOG_INFO("P-State HWP enabled\n");
	}

	if (c & CPU_FEATURE_HWP_EPP) {
		// for maximum performance we have to clear BIAS
		wrmsr(MSR_IA32_ENERGY_PERF_BIAS, 0);
		if (out)
			LOG_INFO("Found Performance and Energy Bias Hint support: 0x%llx\n", rdmsr(MSR_IA32_ENERGY_PERF_BIAS));
	}

	if (c & CPU_FEATURE_ARAT)
		LOG_INFO("Timer runs with a constant rate!");
	else
		LOG_INFO("Timer doesn't run with a constant rate!");

#if 0
	if (out) {
		LOG_INFO("CPU features 6: 0x%x, 0x%x, 0x%x, 0x%x\n", a, b, c, d);
		LOG_INFO("MSR_PLATFORM_INFO 0x%llx\n", rdmsr(MSR_PLATFORM_INFO));
	}
#endif

	max_pstate = get_max_pstate();
	min_pstate = get_min_pstate();
	turbo_pstate = get_turbo_pstate();

	// set maximum p-state to get peak performance
	if (is_turbo)
		set_pstate(turbo_pstate);
	else
		set_pstate(max_pstate);

	if (out)
		dump_pstate();

	return;
}

int reset_fsgs(int32_t core_id)
{
	writefs(0);
#if MAX_CORES > 1
	writegs(core_id * ((size_t) &percore_end0 - (size_t) &percore_start));
#else
	writegs(0);
#endif
	wrmsr(MSR_KERNEL_GS_BASE, 0);

	return 0;
}

int cpu_detection(void) {
	uint64_t xcr0;
	uint32_t a=0, b=0, c=0, d=0, level = 0, extended = 0;
	uint32_t family, model, stepping;
	size_t cr0, cr4;
	uint8_t first_time = 0;

	if (!cpu_info.feature1) {
		first_time = 1;

		cpuid(0, &level, (uint32_t*) cpu_vendor, (uint32_t*)(cpu_vendor+8), (uint32_t*)(cpu_vendor+4));
		kprintf("cpuid level %d\n", level);
		kprintf("CPU vendor: %s\n", cpu_vendor);

		cpuid(1, &a, &b, &cpu_info.feature2, &cpu_info.feature1);

		family   = (a & 0x00000F00) >> 8;
		model    = (a & 0x000000F0) >> 4;
		stepping =  a & 0x0000000F;
		if ((family == 6) && (model < 3) && (stepping < 3))
			cpu_info.feature1 &= ~CPU_FEATURE_SEP;

		cpuid(0x80000000, &extended, &b, &c, &d);
		if (extended >= 0x80000001)
			cpuid(0x80000001, &a, &b, &c, &cpu_info.feature3);
		if (extended >= 0x80000004) {
			uint32_t* bint = (uint32_t*) cpu_brand;

			cpuid(0x80000002, bint+0, bint+1, bint+2, bint+3);
			cpuid(0x80000003, bint+4, bint+5, bint+6, bint+7);
			cpuid(0x80000004, bint+8, bint+9, bint+10, bint+11);
			kprintf("Processor: %s\n", cpu_brand);
		}
		if (extended >= 0x80000008)
			cpuid(0x80000008, &cpu_info.addr_width, &b, &c, &d);

		/* Additional Intel-defined flags: level 0x00000007 */
		if (level >= 0x00000007) {
			a = b = c = d = 0;
			cpuid(7, &a, &cpu_info.feature4, &c, &d);
		}
	}

	if (first_time) {
		kprintf("Paging features: %s%s%s%s%s%s%s%s\n",
				(cpu_info.feature1 & CPU_FEATURE_PSE) ? "PSE (2/4Mb) " : "",
				(cpu_info.feature1 & CPU_FEATURE_PAE) ? "PAE " : "",
				(cpu_info.feature1 & CPU_FEATURE_PGE) ? "PGE " : "",
				(cpu_info.feature1 & CPU_FEATURE_PAT) ? "PAT " : "",
				(cpu_info.feature1 & CPU_FEATURE_PSE36) ? "PSE36 " : "",
				(cpu_info.feature3 & CPU_FEATURE_NX) ? "NX " : "",
				(cpu_info.feature3 & CPU_FEATURE_1GBHP) ? "PSE (1Gb) " : "",
				(cpu_info.feature3 & CPU_FEATURE_LM) ? "LM" : "");

		kprintf("Physical adress-width: %u bits\n", cpu_info.addr_width & 0xff);
		kprintf("Linear adress-width: %u bits\n", (cpu_info.addr_width >> 8) & 0xff);
		kprintf("Sysenter instruction: %s\n", (cpu_info.feature1 & CPU_FEATURE_SEP) ? "available" : "unavailable");
		kprintf("Syscall instruction: %s\n", (cpu_info.feature3 & CPU_FEATURE_SYSCALL) ? "available" : "unavailable");
	}

	//TODO: add check for SMEP, PCE and SMAP

	// be sure that AM, NE and MP is enabled
	cr0 = read_cr0();
	cr0 |= CR0_AM;
	cr0 |= CR0_NE;
	cr0 |= CR0_MP;
	cr0 &= ~(CR0_CD|CR0_NW);
	write_cr0(cr0);

	cr4 = read_cr4();
	if (has_fxsr())
		cr4 |= CR4_OSFXSR;	// set the OSFXSR bit
	if (has_sse())
		cr4 |= CR4_OSXMMEXCPT;	// set the OSXMMEXCPT bit
	if (has_xsave())
		cr4 |= CR4_OSXSAVE;
	if (has_pge())
		cr4 |= CR4_PGE;
	if (has_fsgsbase())
		cr4 |= CR4_FSGSBASE;
	if (has_mce())
		cr4 |= CR4_MCE;		// enable machine check exceptions
	//if (has_vmx())
	//	cr4 |= CR4_VMXE;
	cr4 &= ~(CR4_PCE|CR4_TSD);	// disable performance monitoring counter
								// clear TSD => every privilege level is able
								// to use rdtsc
	write_cr4(cr4);


	if (first_time && has_fsgsbase())
	{
		readfs = rdfsbase;
		readgs = rdgsbase;
		writefs = wrfsbase;
		writegs = wrgsbase;

		// enable the usage of fsgsbase during a context switch
		// => replace short jump with nops
		// => see entry.asm
		memset(&Lpatch0, 0x90, 2);
		memset(&Lpatch1, 0x90, 2);
		memset(&Lpatch2, 0x90, 2);
	}

	if (has_xsave())
	{
		xcr0 = xgetbv(0);
		if (has_fpu())
			xcr0 |= 0x1;
		if (has_sse())
			xcr0 |= 0x2;
		if (has_avx())
			xcr0 |= 0x4;
		if (has_avx512f())
			xcr0 |= 0xE0;
		xsetbv(0, xcr0);

		if (first_time)
			kprintf("Set XCR0 to 0x%llx\n", xgetbv(0));
	}

	// libos => currently no support of syscalls
#if 0
	if (cpu_info.feature3 & CPU_FEATURE_SYSCALL) {
		wrmsr(MSR_EFER, rdmsr(MSR_EFER) | EFER_LMA | EFER_LME | EFER_SCE);
		wrmsr(MSR_STAR, (0x1BULL << 48) | (0x08ULL << 32));
		wrmsr(MSR_LSTAR, (size_t) &isrsyscall);
		//  clear IF flag during an interrupt
		wrmsr(MSR_SYSCALL_MASK, EFLAGS_TF|EFLAGS_DF|EFLAGS_IF|EFLAGS_AC|EFLAGS_NT);
	} else kprintf("Processor doesn't support syscalls\n");
#endif

	if (has_nx())
		wrmsr(MSR_EFER, rdmsr(MSR_EFER) | EFER_NXE);

	//if (has_vmx())
	//	wrmsr(MSR_IA32_FEATURE_CONTROL, rdmsr(MSR_IA32_FEATURE_CONTROL) | 0x5);

	reset_fsgs(atomic_int32_read(&current_boot_id));

	LOG_INFO("Core %d set per_core offset to 0x%x\n", atomic_int32_read(&current_boot_id), rdmsr(MSR_GS_BASE));

	/* set core id to the current boot id */
	set_per_core(__core_id, atomic_int32_read(&current_boot_id));
	LOG_INFO("Core id is set to %d\n", CORE_ID);

	if (has_fpu()) {
		if (first_time)
			LOG_INFO("Found and initialized FPU!\n");
		asm volatile ("fninit");
	}

	if (first_time) {
		// reload feature list because we enabled OSXSAVE
		a = b = c = d = 0;
                cpuid(1, &a, &b, &cpu_info.feature2, &cpu_info.feature1);

		LOG_INFO("CPU features: %s%s%s%s%s%s%s%s%s%s%s%s%s%s%s%s%s%s%s%s%s%s%s%s%s%s%s%s%s%s%s%s%s%s%s%s\n",
			has_sse() ? "SSE " : "",
			has_sse2() ? "SSE2 " : "",
			has_sse3() ? "SSE3 " : "",
			has_sse4_1() ? "SSE4.1 " : "",
			has_sse4_2() ? "SSE4.2 " : "",
			has_avx() ? "AVX " : "",
			has_avx2() ? "AVX2 " : "",
			has_rdrand() ? "RDRAND " : "",
			has_fma() ? "FMA " : "",
			has_movbe() ? "MOVBE " : "",
			has_x2apic() ? "X2APIC " : "",
			has_mce() ? "MCE " : "",
			has_fpu() ? "FPU " : "",
			has_fxsr() ? "FXSR " : "",
			has_xsave() ? "XSAVE " : "",
			has_osxsave() ? "OSXSAVE " : "",
			has_vmx() ? "VMX " : "",
			has_rdtscp() ? "RDTSCP " : "",
			has_fsgsbase() ? "FSGSBASE " : "",
			has_sgx() ? "SGX " : "",
			has_mwait() ? "MWAIT " : "",
			has_clflush() ? "CLFLUSH " : "",
			has_bmi1() ? "BMI1 " : "",
			has_bmi2() ? "BMI2 " : "",
			has_dca() ? "DCA " : "",
			has_rtm() ? "RTM " : "",
			has_hle() ? "HLE " : "",
			has_cqm() ? "CQM " : "",
			has_clflushopt() ? "CLFLUSHOPT " : "",
			has_clwb() ? "CLWB " : "",
			has_avx512f() ? "AVX512F " : "",
			has_avx512cd() ? "AVX512CD " : "",
			has_avx512pf() ? "AVX512PF " : "",
			has_avx512er() ? "AVX512ER " : "",
			has_avx512vl() ? "AVX512VL " : "",
			has_avx512bw() ? "AVX512BW " : "");
	}

	if (first_time && has_osxsave()) {
		a = b = d = 0;
		c = 2;
		cpuid(0xd, &a, &b, &c, &d);
		LOG_INFO("Ext_Save_Area_2: offset %d, size %d\n", b, a);

		a = b = d = 0;
		c = 3;
		cpuid(0xd, &a, &b, &c, &d);
		LOG_INFO("Ext_Save_Area_3: offset %d, size %d\n", b, a);

		a = b = d = 0;
		c = 4;
		cpuid(0xd, &a, &b, &c, &d);
		LOG_INFO("Ext_Save_Area_4: offset %d, size %d\n", b, a);

		save_fpu_state = save_fpu_state_xsave;
		restore_fpu_state = restore_fpu_state_xsave;
		fpu_init = fpu_init_xsave;
	} else if (first_time && has_fxsr()) {
		save_fpu_state = save_fpu_state_fxsr;
		restore_fpu_state = restore_fpu_state_fxsr;
		fpu_init = fpu_init_fxsr;
	}

	// initialize Enhanced SpeedStep Technology
	check_est(first_time);

	if (first_time && on_hypervisor()) {
		char vendor_id[13];

		LOG_INFO("HermitCore is running on a hypervisor!\n");

		cpuid(0x40000000, &a, (uint32_t*)vendor_id, (uint32_t*)(vendor_id+4), (uint32_t*)(vendor_id+8));
		vendor_id[12] = '\0';

		LOG_INFO("Hypervisor Vendor Id: %s\n", vendor_id);
		LOG_INFO("Maximum input value for hypervisor: 0x%x\n", a);
	}


	if (first_time) {
		LOG_INFO("CR0 0x%llx, CR4 0x%llx\n", read_cr0(), read_cr4());
		LOG_INFO("size of xsave_t: %d\n", sizeof(xsave_t));
		if (has_msr()) {
			uint64_t msr;

			LOG_INFO("IA32_MISC_ENABLE 0x%llx\n", rdmsr(MSR_IA32_MISC_ENABLE));
			LOG_INFO("IA32_PLATFORM_ID 0x%llx\n", rdmsr(MSR_IA32_PLATFORM_ID));
			if (has_pat()) {
				msr = rdmsr(MSR_IA32_CR_PAT);

				LOG_INFO("IA32_CR_PAT 0x%llx\n", msr);
				LOG_INFO("PAT use per default %s\n", (msr & 0xF) == 0x6 ? "writeback." : "NO writeback!");
			}

			msr = rdmsr(MSR_MTRRdefType);
			LOG_INFO("MTRR is %s.\n", (msr & (1 << 11)) ? "enabled" : "disabled");
			LOG_INFO("Fixed-range MTRR is %s.\n", (msr & (1 << 10)) ? "enabled" : "disabled");
			LOG_INFO("MTRR used per default %s\n", (msr & 0xFF) == 0x6 ? "writeback." : "NO writeback!");
#if 0
			if (msr & (1 << 10)) {
				LOG_INFO("MSR_MTRRfix64K_00000 0x%llx\n", rdmsr(MSR_MTRRfix64K_00000));
				LOG_INFO("MSR_MTRRfix16K_80000 0x%llx\n", rdmsr(MSR_MTRRfix16K_80000));
				LOG_INFO("MSR_MTRRfix16K_A0000 0x%llx\n", rdmsr(MSR_MTRRfix16K_A0000));
				LOG_INFO("MSR_MTRRfix4K_C0000 0x%llx\n", rdmsr(MSR_MTRRfix4K_C0000));
				LOG_INFO("MSR_MTRRfix4K_C8000 0x%llx\n", rdmsr(MSR_MTRRfix4K_C8000));
				LOG_INFO("MSR_MTRRfix4K_D0000 0x%llx\n", rdmsr(MSR_MTRRfix4K_D0000));
				LOG_INFO("MSR_MTRRfix4K_D8000 0x%llx\n", rdmsr(MSR_MTRRfix4K_D8000));
				LOG_INFO("MSR_MTRRfix4K_E0000 0x%llx\n", rdmsr(MSR_MTRRfix4K_E0000));
				LOG_INFO("MSR_MTRRfix4K_E8000 0x%llx\n", rdmsr(MSR_MTRRfix4K_E8000));
				LOG_INFO("MSR_MTRRfix4K_F0000 0x%llx\n", rdmsr(MSR_MTRRfix4K_F0000));
				LOG_INFO("MSR_MTRRfix4K_F8000 0x%llx\n", rdmsr(MSR_MTRRfix4K_F8000));
			}
#endif
		}
	}

	return 0;
}

uint32_t get_cpu_frequency(void)
{
	if (cpu_freq > 0)
		return cpu_freq;

	return detect_cpu_frequency();
}

void udelay(uint32_t usecs)
{
	if (has_rdtscp()) {
		uint64_t diff, end, start = rdtscp(NULL);
		uint64_t deadline = get_cpu_frequency() * usecs;

		do {
			end = rdtscp(NULL);
			rmb();
			diff = end > start ? end - start : start - end;
			if ((diff < deadline) && (deadline - diff > 50000))
				check_workqueues();
		} while(diff < deadline);
	} else {
		uint64_t diff, end, start = rdtsc();
		uint64_t deadline = get_cpu_frequency() * usecs;

		do {
			mb();
			end = rdtsc();
			diff = end > start ? end - start : start - end;
			if ((diff < deadline) && (deadline - diff > 50000))
				check_workqueues();
		} while(diff < deadline);
	}
}