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         WARN_ONCE(1, "\"no-hlt\" is deprecated, please use \"idle=poll\"\n");
  23         boot_cpu_data.hlt_works_ok = 0;
  24         return 1;
  25 }
  26
  27 __setup("no-hlt", no_halt);
  28
  29 static int __init no_387(char *s)
  30 {
  31         boot_cpu_data.hard_math = 0;
  32         write_cr0(X86_CR0_TS | X86_CR0_EM | X86_CR0_MP | read_cr0());
  33         return 1;
  34 }
  35
  36 __setup("no387", no_387);
  37
  38 static double __initdata x = 4195835.0;
  39 static double __initdata y = 3145727.0;
  40
  41 /*
  42  * This used to check for exceptions..
  43  * However, it turns out that to support that,
  44  * the XMM trap handlers basically had to
  45  * be buggy. So let's have a correct XMM trap
  46  * handler, and forget about printing out
  47  * some status at boot.
  48  *
  49  * We should really only care about bugs here
  50  * anyway. Not features.
  51  */
  52 static void __init check_fpu(void)
  53 {
  54         s32 fdiv_bug;
  55
  56         if (!boot_cpu_data.hard_math) {
  57 #ifndef CONFIG_MATH_EMULATION
  58                 pr_emerg("No coprocessor found and no math emulation present\n");
  59                 pr_emerg("Giving up\n");
  60                 for (;;) ;
  61 #endif
  62                 return;
  63         }
  64
  65         kernel_fpu_begin();
  66
  67         /*
  68          * trap_init() enabled FXSR and company _before_ testing for FP
  69          * problems here.
  70          *
  71          * Test for the divl bug..
  72          */
  73         __asm__("fninit\n\t"
  74                 "fldl %1\n\t"
  75                 "fdivl %2\n\t"
  76                 "fmull %2\n\t"
  77                 "fldl %1\n\t"
  78                 "fsubp %%st,%%st(1)\n\t"
  79                 "fistpl %0\n\t"
  80                 "fwait\n\t"
  81                 "fninit"
  82                 : "=m" (*&fdiv_bug)
  83                 : "m" (*&x), "m" (*&y));
  84
  85         kernel_fpu_end();
  86
  87         boot_cpu_data.fdiv_bug = fdiv_bug;
  88         if (boot_cpu_data.fdiv_bug)
  89                 pr_warn("Hmm, FPU with FDIV bug\n");
  90 }
  91
  92 static void __init check_hlt(void)
  93 {
  94         if (boot_cpu_data.x86 >= 5 || paravirt_enabled())
  95                 return;
  96
  97         pr_info("Checking 'hlt' instruction... ");
  98         if (!boot_cpu_data.hlt_works_ok) {
  99                 pr_cont("disabled\n");
 100                 return;
 101         }
 102         halt();
 103         halt();
 104         halt();
 105         halt();
 106         pr_cont("OK\n");
 107 }
 108
 109 /*
 110  *      Most 386 processors have a bug where a POPAD can lock the
 111  *      machine even from user space.
 112  */
 113
 114 static void __init check_popad(void)
 115 {
 116 #ifndef CONFIG_X86_POPAD_OK
 117         int res, inp = (int) &res;
 118
 119         pr_info("Checking for popad bug... ");
 120         __asm__ __volatile__(
 121           "movl $12345678,%%eax; movl $0,%%edi; pusha; popa; movl (%%edx,%%edi),%%ecx "
 122           : "=&a" (res)
 123           : "d" (inp)
 124           : "ecx", "edi");
 125         /*
 126          * If this fails, it means that any user program may lock the
 127          * CPU hard. Too bad.
 128          */
 129         if (res != 12345678)
 130                 pr_cont("Buggy\n");
 131         else
 132                 pr_cont("OK\n");
 133 #endif
 134 }
 135
 136 /*
 137  * Check whether we are able to run this kernel safely on SMP.
 138  *
 139  * - In order to run on a i386, we need to be compiled for i386
 140  *   (for due to lack of "invlpg" and working WP on a i386)
 141  * - In order to run on anything without a TSC, we need to be
 142  *   compiled for a i486.
 143  */
 144
 145 static void __init check_config(void)
 146 {
 147 /*
 148  * We'd better not be a i386 if we're configured to use some
 149  * i486+ only features! (WP works in supervisor mode and the
 150  * new "invlpg" and "bswap" instructions)
 151  */
 152 #if defined(CONFIG_X86_WP_WORKS_OK) || defined(CONFIG_X86_INVLPG) || \
 153         defined(CONFIG_X86_BSWAP)
 154         if (boot_cpu_data.x86 == 3)
 155                 panic("Kernel requires i486+ for 'invlpg' and other features");
 156 #endif
 157 }
 158
 159
 160 void __init check_bugs(void)
 161 {
 162         identify_boot_cpu();
 163 #ifndef CONFIG_SMP
 164         pr_info("CPU: ");
 165         print_cpu_info(&boot_cpu_data);
 166 #endif
 167         check_config();
 168         check_hlt();
 169         check_popad();
 170         init_utsname()->machine[1] =
 171                 '0' + (boot_cpu_data.x86 > 6 ? 6 : boot_cpu_data.x86);
 172         alternative_instructions();
 173
 174         /*
 175          * kernel_fpu_begin/end() in check_fpu() relies on the patched
 176          * alternative instructions.
 177          */
 178         check_fpu();
 179 }