arch/x86/kernel/cpu/bugs.c

   1 /*
   2  *  Copyright (C) 1994  Linus Torvalds
   3  *
   4  *  Cyrix stuff, June 1998 by:
   5  *      - Rafael R. Reilova (moved everything from head.S),
   6  *        <rreilova@ececs.uc.edu>
   7  *      - Channing Corn (tests & fixes),
   8  *      - Andrew D. Balsa (code cleanup).
   9  */
  10 #include <linux/init.h>
  11 #include <linux/utsname.h>
  12 #include <asm/bugs.h>
  13 #include <asm/processor.h>
  14 #include <asm/processor-flags.h>
  15 #include <asm/i387.h>
  16 #include <asm/msr.h>
  17 #include <asm/paravirt.h>
  18 #include <asm/alternative.h>
  19
  20 static int __init no_halt(char *s)
  21 {
  22         boot_cpu_data.hlt_works_ok = 0;
  23         return 1;
  24 }
  25
  26 __setup("no-hlt", no_halt);
  27
  28 static int __init no_387(char *s)
  29 {
  30         boot_cpu_data.hard_math = 0;
  31         write_cr0(X86_CR0_TS | X86_CR0_EM | X86_CR0_MP | read_cr0());
  32         return 1;
  33 }
  34
  35 __setup("no387", no_387);
  36
  37 static double __initdata x = 4195835.0;
  38 static double __initdata y = 3145727.0;
  39
  40 /*
  41  * This used to check for exceptions..
  42  * However, it turns out that to support that,
  43  * the XMM trap handlers basically had to
  44  * be buggy. So let's have a correct XMM trap
  45  * handler, and forget about printing out
  46  * some status at boot.
  47  *
  48  * We should really only care about bugs here
  49  * anyway. Not features.
  50  */
  51 static void __init check_fpu(void)
  52 {
  53         s32 fdiv_bug;
  54
  55         if (!boot_cpu_data.hard_math) {
  56 #ifndef CONFIG_MATH_EMULATION
  57                 printk(KERN_EMERG "No coprocessor found and no math emulation present.\n");
  58                 printk(KERN_EMERG "Giving up.\n");
  59                 for (;;) ;
  60 #endif
  61                 return;
  62         }
  63
  64         /*
  65          * trap_init() enabled FXSR and company _before_ testing for FP
  66          * problems here.
  67          *
  68          * Test for the divl bug..
  69          */
  70         __asm__("fninit\n\t"
  71                 "fldl %1\n\t"
  72                 "fdivl %2\n\t"
  73                 "fmull %2\n\t"
  74                 "fldl %1\n\t"
  75                 "fsubp %%st,%%st(1)\n\t"
  76                 "fistpl %0\n\t"
  77                 "fwait\n\t"
  78                 "fninit"
  79                 : "=m" (*&fdiv_bug)
  80                 : "m" (*&x), "m" (*&y));
  81
  82         boot_cpu_data.fdiv_bug = fdiv_bug;
  83         if (boot_cpu_data.fdiv_bug)
  84                 printk(KERN_WARNING "Hmm, FPU with FDIV bug.\n");
  85 }
  86
  87 static void __init check_hlt(void)
  88 {
  89         if (paravirt_enabled())
  90                 return;
  91
  92         printk(KERN_INFO "Checking 'hlt' instruction... ");
  93         if (!boot_cpu_data.hlt_works_ok) {
  94                 printk("disabled\n");
  95                 return;
  96         }
  97         halt();
  98         halt();
  99         halt();
 100         halt();
 101         printk(KERN_CONT "OK.\n");
 102 }
 103
 104 /*
 105  *      Most 386 processors have a bug where a POPAD can lock the
 106  *      machine even from user space.
 107  */
 108
 109 static void __init check_popad(void)
 110 {
 111 #ifndef CONFIG_X86_POPAD_OK
 112         int res, inp = (int) &res;
 113
 114         printk(KERN_INFO "Checking for popad bug... ");
 115         __asm__ __volatile__(
 116           "movl $12345678,%%eax; movl $0,%%edi; pusha; popa; movl (%%edx,%%edi),%%ecx "
 117           : "=&a" (res)
 118           : "d" (inp)
 119           : "ecx", "edi");
 120         /*
 121          * If this fails, it means that any user program may lock the
 122          * CPU hard. Too bad.
 123          */
 124         if (res != 12345678)
 125                 printk(KERN_CONT "Buggy.\n");
 126         else
 127                 printk(KERN_CONT "OK.\n");
 128 #endif
 129 }
 130
 131 /*
 132  * Check whether we are able to run this kernel safely on SMP.
 133  *
 134  * - In order to run on a i386, we need to be compiled for i386
 135  *   (for due to lack of "invlpg" and working WP on a i386)
 136  * - In order to run on anything without a TSC, we need to be
 137  *   compiled for a i486.
 138  */
 139
 140 static void __init check_config(void)
 141 {
 142 /*
 143  * We'd better not be a i386 if we're configured to use some
 144  * i486+ only features! (WP works in supervisor mode and the
 145  * new "invlpg" and "bswap" instructions)
 146  */
 147 #if defined(CONFIG_X86_WP_WORKS_OK) || defined(CONFIG_X86_INVLPG) || \
 148         defined(CONFIG_X86_BSWAP)
 149         if (boot_cpu_data.x86 == 3)
 150                 panic("Kernel requires i486+ for 'invlpg' and other features");
 151 #endif
 152 }
 153
 154
 155 void __init check_bugs(void)
 156 {
 157         identify_boot_cpu();
 158 #ifndef CONFIG_SMP
 159         printk(KERN_INFO "CPU: ");
 160         print_cpu_info(&boot_cpu_data);
 161 #endif
 162         check_config();
 163         check_fpu();
 164         check_hlt();
 165         check_popad();
 166         init_utsname()->machine[1] =
 167                 '0' + (boot_cpu_data.x86 > 6 ? 6 : boot_cpu_data.x86);
 168         alternative_instructions();
 169 }