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         if (!boot_cpu_data.hard_math) {
  54 #ifndef CONFIG_MATH_EMULATION
  55                 printk(KERN_EMERG "No coprocessor found and no math emulation present.\n");
  56                 printk(KERN_EMERG "Giving up.\n");
  57                 for (;;) ;
  58 #endif
  59                 return;
  60         }
  61
  62         /*
  63          * trap_init() enabled FXSR and company _before_ testing for FP
  64          * problems here.
  65          *
  66          * Test for the divl bug..
  67          */
  68         __asm__("fninit\n\t"
  69                 "fldl %1\n\t"
  70                 "fdivl %2\n\t"
  71                 "fmull %2\n\t"
  72                 "fldl %1\n\t"
  73                 "fsubp %%st,%%st(1)\n\t"
  74                 "fistpl %0\n\t"
  75                 "fwait\n\t"
  76                 "fninit"
  77                 : "=m" (*&boot_cpu_data.fdiv_bug)
  78                 : "m" (*&x), "m" (*&y));
  79         if (boot_cpu_data.fdiv_bug)
  80                 printk("Hmm, FPU with FDIV bug.\n");
  81 }
  82
  83 static void __init check_hlt(void)
  84 {
  85         if (paravirt_enabled())
  86                 return;
  87
  88         printk(KERN_INFO "Checking 'hlt' instruction... ");
  89         if (!boot_cpu_data.hlt_works_ok) {
  90                 printk("disabled\n");
  91                 return;
  92         }
  93         halt();
  94         halt();
  95         halt();
  96         halt();
  97         printk("OK.\n");
  98 }
  99
 100 /*
 101  *      Most 386 processors have a bug where a POPAD can lock the
 102  *      machine even from user space.
 103  */
 104
 105 static void __init check_popad(void)
 106 {
 107 #ifndef CONFIG_X86_POPAD_OK
 108         int res, inp = (int) &res;
 109
 110         printk(KERN_INFO "Checking for popad bug... ");
 111         __asm__ __volatile__(
 112           "movl $12345678,%%eax; movl $0,%%edi; pusha; popa; movl (%%edx,%%edi),%%ecx "
 113           : "=&a" (res)
 114           : "d" (inp)
 115           : "ecx", "edi");
 116         /*
 117          * If this fails, it means that any user program may lock the
 118          * CPU hard. Too bad.
 119          */
 120         if (res != 12345678)
 121                 printk("Buggy.\n");
 122         else
 123                 printk("OK.\n");
 124 #endif
 125 }
 126
 127 /*
 128  * Check whether we are able to run this kernel safely on SMP.
 129  *
 130  * - In order to run on a i386, we need to be compiled for i386
 131  *   (for due to lack of "invlpg" and working WP on a i386)
 132  * - In order to run on anything without a TSC, we need to be
 133  *   compiled for a i486.
 134  * - In order to support the local APIC on a buggy Pentium machine,
 135  *   we need to be compiled with CONFIG_X86_GOOD_APIC disabled,
 136  *   which happens implicitly if compiled for a Pentium or lower
 137  *   (unless an advanced selection of CPU features is used) as an
 138  *   otherwise config implies a properly working local APIC without
 139  *   the need to do extra reads from the APIC.
 140 */
 141
 142 static void __init check_config(void)
 143 {
 144 /*
 145  * We'd better not be a i386 if we're configured to use some
 146  * i486+ only features! (WP works in supervisor mode and the
 147  * new "invlpg" and "bswap" instructions)
 148  */
 149 #if defined(CONFIG_X86_WP_WORKS_OK) || defined(CONFIG_X86_INVLPG) || \
 150         defined(CONFIG_X86_BSWAP)
 151         if (boot_cpu_data.x86 == 3)
 152                 panic("Kernel requires i486+ for 'invlpg' and other features");
 153 #endif
 154
 155 /*
 156  * If we were told we had a good local APIC, check for buggy Pentia,
 157  * i.e. all B steppings and the C2 stepping of P54C when using their
 158  * integrated APIC (see 11AP erratum in "Pentium Processor
 159  * Specification Update").
 160  */
 161 #if defined(CONFIG_X86_LOCAL_APIC) && defined(CONFIG_X86_GOOD_APIC)
 162         if (boot_cpu_data.x86_vendor == X86_VENDOR_INTEL
 163             && cpu_has_apic
 164             && boot_cpu_data.x86 == 5
 165             && boot_cpu_data.x86_model == 2
 166             && (boot_cpu_data.x86_mask < 6 || boot_cpu_data.x86_mask == 11))
 167                 panic("Kernel compiled for PMMX+, assumes a local APIC without the read-before-write bug!");
 168 #endif
 169 }
 170
 171
 172 void __init check_bugs(void)
 173 {
 174         identify_boot_cpu();
 175 #ifndef CONFIG_SMP
 176         printk("CPU: ");
 177         print_cpu_info(&boot_cpu_data);
 178 #endif
 179         check_config();
 180         check_fpu();
 181         check_hlt();
 182         check_popad();
 183         init_utsname()->machine[1] =
 184                 '0' + (boot_cpu_data.x86 > 6 ? 6 : boot_cpu_data.x86);
 185         alternative_instructions();
 186 }