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