arch/x86/boot/cpuflags.c

// SPDX-License-Identifier: GPL-2.0
#include <linux/types.h>
#include "bitops.h"

#include <asm/processor-flags.h>
#include <asm/required-features.h>
#include <asm/msr-index.h>
#include "cpuflags.h"

struct cpu_features cpu;
u32 cpu_vendor[3];

static bool loaded_flags;

static int has_fpu(void)
{
	u16 fcw = -1, fsw = -1;
	unsigned long cr0;

	asm volatile("mov %%cr0,%0" : "=r" (cr0));
	if (cr0 & (X86_CR0_EM|X86_CR0_TS)) {
		cr0 &= ~(X86_CR0_EM|X86_CR0_TS);
		asm volatile("mov %0,%%cr0" : : "r" (cr0));
	}

	asm volatile("fninit ; fnstsw %0 ; fnstcw %1"
		     : "+m" (fsw), "+m" (fcw));

	return fsw == 0 && (fcw & 0x103f) == 0x003f;
}

/*
 * For building the 16-bit code we want to explicitly specify 32-bit
 * push/pop operations, rather than just saying 'pushf' or 'popf' and
 * letting the compiler choose. But this is also included from the
 * compressed/ directory where it may be 64-bit code, and thus needs
 * to be 'pushfq' or 'popfq' in that case.
 */
#ifdef __x86_64__
#define PUSHF "pushfq"
#define POPF "popfq"
#else
#define PUSHF "pushfl"
#define POPF "popfl"
#endif

int has_eflag(unsigned long mask)
{
	unsigned long f0, f1;

	asm volatile(PUSHF "	\n\t"
		     PUSHF "	\n\t"
		     "pop %0	\n\t"
		     "mov %0,%1	\n\t"
		     "xor %2,%1	\n\t"
		     "push %1	\n\t"
		     POPF "	\n\t"
		     PUSHF "	\n\t"
		     "pop %1	\n\t"
		     POPF
		     : "=&r" (f0), "=&r" (f1)
		     : "ri" (mask));

	return !!((f0^f1) & mask);
}

void cpuid_count(u32 id, u32 count, u32 *a, u32 *b, u32 *c, u32 *d)
{
	asm volatile("cpuid"
		     : "=a" (*a), "=b" (*b), "=c" (*c), "=d" (*d)
		     : "0" (id), "2" (count)
	);
}

#define cpuid(id, a, b, c, d) cpuid_count(id, 0, a, b, c, d)

void get_cpuflags(void)
{
	u32 max_intel_level, max_amd_level;
	u32 tfms;
	u32 ignored;

	if (loaded_flags)
		return;
	loaded_flags = true;

	if (has_fpu())
		set_bit(X86_FEATURE_FPU, cpu.flags);

	if (has_eflag(X86_EFLAGS_ID)) {
		cpuid(0x0, &max_intel_level, &cpu_vendor[0], &cpu_vendor[2],
		      &cpu_vendor[1]);

		if (max_intel_level >= 0x00000001 &&
		    max_intel_level <= 0x0000ffff) {
			cpuid(0x1, &tfms, &ignored, &cpu.flags[4],
			      &cpu.flags[0]);
			cpu.level = (tfms >> 8) & 15;
			cpu.family = cpu.level;
			cpu.model = (tfms >> 4) & 15;
			if (cpu.level >= 6)
				cpu.model += ((tfms >> 16) & 0xf) << 4;
		}

		if (max_intel_level >= 0x00000007) {
			cpuid_count(0x00000007, 0, &ignored, &ignored,
					&cpu.flags[16], &ignored);
		}

		cpuid(0x80000000, &max_amd_level, &ignored, &ignored,
		      &ignored);

		if (max_amd_level >= 0x80000001 &&
		    max_amd_level <= 0x8000ffff) {
			cpuid(0x80000001, &ignored, &ignored, &cpu.flags[6],
			      &cpu.flags[1]);
		}
	}
}