linux/arch/x86/kernel/cpu/bugs.c

/*
 *  Copyright (C) 1994  Linus Torvalds
 *
 *  Cyrix stuff, June 1998 by:
 *	- Rafael R. Reilova (moved everything from head.S),
 *        <rreilova@ececs.uc.edu>
 *	- Channing Corn (tests & fixes),
 *	- Andrew D. Balsa (code cleanup).
 */
#include <linux/init.h>
#include <linux/utsname.h>
#include <asm/bugs.h>
#include <asm/processor.h>
#include <asm/processor-flags.h>
#include <asm/i387.h>
#include <asm/msr.h>
#include <asm/paravirt.h>
#include <asm/alternative.h>

static int __init no_387(char *s)
{
	boot_cpu_data.hard_math = 0;
	write_cr0(X86_CR0_TS | X86_CR0_EM | X86_CR0_MP | read_cr0());
	return 1;
}

__setup("no387", no_387);

static double __initdata x = 4195835.0;
static double __initdata y = 3145727.0;

/*
 * This used to check for exceptions..
 * However, it turns out that to support that,
 * the XMM trap handlers basically had to
 * be buggy. So let's have a correct XMM trap
 * handler, and forget about printing out
 * some status at boot.
 *
 * We should really only care about bugs here
 * anyway. Not features.
 */
static void __init check_fpu(void)
{
	s32 fdiv_bug;

	if (!boot_cpu_data.hard_math) {
#ifndef CONFIG_MATH_EMULATION
		pr_emerg("No coprocessor found and no math emulation present\n");
		pr_emerg("Giving up\n");
		for (;;) ;
#endif
		return;
	}

	kernel_fpu_begin();

	/*
	 * trap_init() enabled FXSR and company _before_ testing for FP
	 * problems here.
	 *
	 * Test for the divl bug: http://en.wikipedia.org/wiki/Fdiv_bug
	 */
	__asm__("fninit\n\t"
		"fldl %1\n\t"
		"fdivl %2\n\t"
		"fmull %2\n\t"
		"fldl %1\n\t"
		"fsubp %%st,%%st(1)\n\t"
		"fistpl %0\n\t"
		"fwait\n\t"
		"fninit"
		: "=m" (*&fdiv_bug)
		: "m" (*&x), "m" (*&y));

	kernel_fpu_end();

	if (fdiv_bug) {
		set_cpu_bug(&boot_cpu_data, X86_BUG_FDIV);
		pr_warn("Hmm, FPU with FDIV bug\n");
	}
}

void __init check_bugs(void)
{
	identify_boot_cpu();
#ifndef CONFIG_SMP
	pr_info("CPU: ");
	print_cpu_info(&boot_cpu_data);
#endif

	/*
	 * Check whether we are able to run this kernel safely on SMP.
	 *
	 * - i386 is no longer supported.
	 * - In order to run on anything without a TSC, we need to be
	 *   compiled for a i486.
	 */
	if (boot_cpu_data.x86 < 4)
		panic("Kernel requires i486+ for 'invlpg' and other features");

	init_utsname()->machine[1] =
		'0' + (boot_cpu_data.x86 > 6 ? 6 : boot_cpu_data.x86);
	alternative_instructions();

	/*
	 * kernel_fpu_begin/end() in check_fpu() relies on the patched
	 * alternative instructions.
	 */
	check_fpu();
}