src/cpu/intel/common/hyperthreading.c

/* SPDX-License-Identifier: GPL-2.0-only */
/* This file is part of the coreboot project. */

#include <cpu/x86/lapic.h>
#include <cpu/intel/common/common.h>
#include <arch/cpu.h>

/*
 * Return true if running thread does not have the smallest lapic ID
 * within a CPU core.
 */
bool intel_ht_sibling(void)
{
	struct cpuid_result result;
	unsigned int core_ids, apic_ids, threads;

	/* Is Hyper-Threading supported */
	if (!(cpuid_edx(1) & CPUID_FEAURE_HTT))
		return false;

	apic_ids = 1;
	if (cpuid_eax(0) >= 1)
		apic_ids = (cpuid_ebx(1) >> 16) & 0xff;
	if (apic_ids == 0)
		apic_ids = 1;

	core_ids = 1;
	if (cpuid_eax(0) >= 4) {
		result = cpuid_ext(4, 0);
		core_ids += (result.eax >> 26) & 0x3f;
	}

	threads = (apic_ids / core_ids);
	return !!(lapicid() & (threads - 1));
}