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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/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 mca_pentium(char *s)
{
      mca_pentium_flag = 1;
      return 1;
}

__setup("mca-pentium", mca_pentium);

static int __init no_387(char *s)
{
      boot_cpu_data.hard_math = 0;
      write_cr0(0xE | 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)
{
      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" (*&boot_cpu_data.fdiv_bug)
            : "m" (*&x), "m" (*&y));
      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.
 * - In order to support the local APIC on a buggy Pentium machine,
 *   we need to be compiled with CONFIG_X86_GOOD_APIC disabled,
 *   which happens implicitly if compiled for a Pentium or lower
 *   (unless an advanced selection of CPU features is used) as an
 *   otherwise config implies a properly working local APIC without
 *   the need to do extra reads from the APIC.
*/

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

/*
 * If we configured ourselves for a TSC, we'd better have one!
 */
#ifdef CONFIG_X86_TSC
      if (!cpu_has_tsc && !tsc_disable)
            panic("Kernel compiled for Pentium+, requires TSC feature!");
#endif

/*
 * If we were told we had a good local APIC, check for buggy Pentia,
 * i.e. all B steppings and the C2 stepping of P54C when using their
 * integrated APIC (see 11AP erratum in "Pentium Processor
 * Specification Update").
 */
#if defined(CONFIG_X86_LOCAL_APIC) && defined(CONFIG_X86_GOOD_APIC)
      if (boot_cpu_data.x86_vendor == X86_VENDOR_INTEL
          && cpu_has_apic
          && boot_cpu_data.x86 == 5
          && boot_cpu_data.x86_model == 2
          && (boot_cpu_data.x86_mask < 6 || boot_cpu_data.x86_mask == 11))
            panic("Kernel compiled for PMMX+, assumes a local APIC without the read-before-write bug!");
#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();
}

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