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_387(char *s)
  21 {
  22         boot_cpu_data.hard_math = 0;
  23         write_cr0(X86_CR0_TS | X86_CR0_EM | X86_CR0_MP | read_cr0());
  24         return 1;
  25 }
  26
  27 __setup("no387", no_387);
  28
  29 static double __initdata x = 4195835.0;
  30 static double __initdata y = 3145727.0;
  31
  32 /*
  33  * This used to check for exceptions..
  34  * However, it turns out that to support that,
  35  * the XMM trap handlers basically had to
  36  * be buggy. So let's have a correct XMM trap
  37  * handler, and forget about printing out
  38  * some status at boot.
  39  *
  40  * We should really only care about bugs here
  41  * anyway. Not features.
  42  */
  43 static void __init check_fpu(void)
  44 {
  45         s32 fdiv_bug;
  46
  47         if (!boot_cpu_data.hard_math) {
  48 #ifndef CONFIG_MATH_EMULATION
  49                 pr_emerg("No coprocessor found and no math emulation present\n");
  50                 pr_emerg("Giving up\n");
  51                 for (;;) ;
  52 #endif
  53                 return;
  54         }
  55
  56         kernel_fpu_begin();
  57
  58         /*
  59          * trap_init() enabled FXSR and company _before_ testing for FP
  60          * problems here.
  61          *
  62          * Test for the divl bug: http://en.wikipedia.org/wiki/Fdiv_bug
  63          */
  64         __asm__("fninit\n\t"
  65                 "fldl %1\n\t"
  66                 "fdivl %2\n\t"
  67                 "fmull %2\n\t"
  68                 "fldl %1\n\t"
  69                 "fsubp %%st,%%st(1)\n\t"
  70                 "fistpl %0\n\t"
  71                 "fwait\n\t"
  72                 "fninit"
  73                 : "=m" (*&fdiv_bug)
  74                 : "m" (*&x), "m" (*&y));
  75
  76         kernel_fpu_end();
  77
  78         if (fdiv_bug) {
  79                 set_cpu_bug(&boot_cpu_data, X86_BUG_FDIV);
  80                 pr_warn("Hmm, FPU with FDIV bug\n");
  81         }
  82 }
  83
  84 void __init check_bugs(void)
  85 {
  86         identify_boot_cpu();
  87 #ifndef CONFIG_SMP
  88         pr_info("CPU: ");
  89         print_cpu_info(&boot_cpu_data);
  90 #endif
  91
  92         /*
  93          * Check whether we are able to run this kernel safely on SMP.
  94          *
  95          * - i386 is no longer supported.
  96          * - In order to run on anything without a TSC, we need to be
  97          *   compiled for a i486.
  98          */
  99         if (boot_cpu_data.x86 < 4)
 100                 panic("Kernel requires i486+ for 'invlpg' and other features");
 101
 102         init_utsname()->machine[1] =
 103                 '0' + (boot_cpu_data.x86 > 6 ? 6 : boot_cpu_data.x86);
 104         alternative_instructions();
 105
 106         /*
 107          * kernel_fpu_begin/end() in check_fpu() relies on the patched
 108          * alternative instructions.
 109          */
 110         check_fpu();
 111 }