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

DEFINITIONS

1. no_halt
2. no_387
3. check_fpu
4. check_hlt
5. check_popad
6. check_config
7. check_bugs

/*
 *  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_halt(char *s)
{
        boot_cpu_data.hlt_works_ok = 0;
        return 1;
}

__setup("no-hlt", no_halt);

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
                printk(KERN_EMERG "No coprocessor found and no math emulation present.\n");
                printk(KERN_EMERG "Giving up.\n");
                for (;;) ;
#endif
                return;
        }

        /*
         * trap_init() enabled FXSR and company _before_ testing for FP
         * problems here.
         *
         * Test for the divl 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));

        boot_cpu_data.fdiv_bug = fdiv_bug;
        if (boot_cpu_data.fdiv_bug)
                printk("Hmm, FPU with FDIV bug.\n");
}

static void __init check_hlt(void)
{
        if (paravirt_enabled())
                return;

        printk(KERN_INFO "Checking 'hlt' instruction... ");
        if (!boot_cpu_data.hlt_works_ok) {
                printk("disabled\n");
                return;
        }
        halt();
        halt();
        halt();
        halt();
        printk("OK.\n");
}

/*
 *      Most 386 processors have a bug where a POPAD can lock the
 *      machine even from user space.
 */

static void __init check_popad(void)
{
#ifndef CONFIG_X86_POPAD_OK
        int res, inp = (int) &res;

        printk(KERN_INFO "Checking for popad bug... ");
        __asm__ __volatile__(
          "movl $12345678,%%eax; movl $0,%%edi; pusha; popa; movl (%%edx,%%edi),%%ecx "
          : "=&a" (res)
          : "d" (inp)
          : "ecx", "edi");
        /*
         * If this fails, it means that any user program may lock the
         * CPU hard. Too bad.
         */
        if (res != 12345678)
                printk("Buggy.\n");
        else
                printk("OK.\n");
#endif
}

/*
 * Check whether we are able to run this kernel safely on SMP.
 *
 * - In order to run on a i386, we need to be compiled for i386
 *   (for due to lack of "invlpg" and working WP on a i386)
 * - In order to run on anything without a TSC, we need to be
 *   compiled for a i486.
 */

static void __init check_config(void)
{
/*
 * We'd better not be a i386 if we're configured to use some
 * i486+ only features! (WP works in supervisor mode and the
 * new "invlpg" and "bswap" instructions)
 */
#if defined(CONFIG_X86_WP_WORKS_OK) || defined(CONFIG_X86_INVLPG) || \
        defined(CONFIG_X86_BSWAP)
        if (boot_cpu_data.x86 == 3)
                panic("Kernel requires i486+ for 'invlpg' and other features");
#endif
}


void __init check_bugs(void)
{
        identify_boot_cpu();
#ifndef CONFIG_SMP
        printk("CPU: ");
        print_cpu_info(&boot_cpu_data);
#endif
        check_config();
        check_fpu();
        check_hlt();
        check_popad();
        init_utsname()->machine[1] =
                '0' + (boot_cpu_data.x86 > 6 ? 6 : boot_cpu_data.x86);
        alternative_instructions();
}