arch/x86/kernel/nmi.c

   1 /*
   2  *  Copyright (C) 1991, 1992  Linus Torvalds
   3  *  Copyright (C) 2000, 2001, 2002 Andi Kleen, SuSE Labs
   4  *  Copyright (C) 2011  Don Zickus Red Hat, Inc.
   5  *
   6  *  Pentium III FXSR, SSE support
   7  *      Gareth Hughes <gareth@valinux.com>, May 2000
   8  */
   9
  10 /*
  11  * Handle hardware traps and faults.
  12  */
  13 #include <linux/spinlock.h>
  14 #include <linux/kprobes.h>
  15 #include <linux/kdebug.h>
  16 #include <linux/nmi.h>
  17 #include <linux/delay.h>
  18 #include <linux/hardirq.h>
  19 #include <linux/slab.h>
  20 #include <linux/export.h>
  21
  22 #include <linux/mca.h>
  23
  24 #if defined(CONFIG_EDAC)
  25 #include <linux/edac.h>
  26 #endif
  27
  28 #include <linux/atomic.h>
  29 #include <asm/traps.h>
  30 #include <asm/mach_traps.h>
  31 #include <asm/nmi.h>
  32
  33 #define NMI_MAX_NAMELEN 16
  34 struct nmiaction {
  35         struct list_head list;
  36         nmi_handler_t handler;
  37         unsigned int flags;
  38         char *name;
  39 };
  40
  41 struct nmi_desc {
  42         spinlock_t lock;
  43         struct list_head head;
  44 };
  45
  46 static struct nmi_desc nmi_desc[NMI_MAX] =
  47 {
  48         {
  49                 .lock = __SPIN_LOCK_UNLOCKED(&nmi_desc[0].lock),
  50                 .head = LIST_HEAD_INIT(nmi_desc[0].head),
  51         },
  52         {
  53                 .lock = __SPIN_LOCK_UNLOCKED(&nmi_desc[1].lock),
  54                 .head = LIST_HEAD_INIT(nmi_desc[1].head),
  55         },
  56
  57 };
  58
  59 struct nmi_stats {
  60         unsigned int normal;
  61         unsigned int unknown;
  62         unsigned int external;
  63         unsigned int swallow;
  64 };
  65
  66 static DEFINE_PER_CPU(struct nmi_stats, nmi_stats);
  67
  68 static int ignore_nmis;
  69
  70 int unknown_nmi_panic;
  71 /*
  72  * Prevent NMI reason port (0x61) being accessed simultaneously, can
  73  * only be used in NMI handler.
  74  */
  75 static DEFINE_RAW_SPINLOCK(nmi_reason_lock);
  76
  77 static int __init setup_unknown_nmi_panic(char *str)
  78 {
  79         unknown_nmi_panic = 1;
  80         return 1;
  81 }
  82 __setup("unknown_nmi_panic", setup_unknown_nmi_panic);
  83
  84 #define nmi_to_desc(type) (&nmi_desc[type])
  85
  86 static int notrace __kprobes nmi_handle(unsigned int type, struct pt_regs *regs, bool b2b)
  87 {
  88         struct nmi_desc *desc = nmi_to_desc(type);
  89         struct nmiaction *a;
  90         int handled=0;
  91
  92         rcu_read_lock();
  93
  94         /*
  95          * NMIs are edge-triggered, which means if you have enough
  96          * of them concurrently, you can lose some because only one
  97          * can be latched at any given time.  Walk the whole list
  98          * to handle those situations.
  99          */
 100         list_for_each_entry_rcu(a, &desc->head, list)
 101                 handled += a->handler(type, regs);
 102
 103         rcu_read_unlock();
 104
 105         /* return total number of NMI events handled */
 106         return handled;
 107 }
 108
 109 static int __setup_nmi(unsigned int type, struct nmiaction *action)
 110 {
 111         struct nmi_desc *desc = nmi_to_desc(type);
 112         unsigned long flags;
 113
 114         spin_lock_irqsave(&desc->lock, flags);
 115
 116         /*
 117          * most handlers of type NMI_UNKNOWN never return because
 118          * they just assume the NMI is theirs.  Just a sanity check
 119          * to manage expectations
 120          */
 121         WARN_ON_ONCE(type == NMI_UNKNOWN && !list_empty(&desc->head));
 122
 123         /*
 124          * some handlers need to be executed first otherwise a fake
 125          * event confuses some handlers (kdump uses this flag)
 126          */
 127         if (action->flags & NMI_FLAG_FIRST)
 128                 list_add_rcu(&action->list, &desc->head);
 129         else
 130                 list_add_tail_rcu(&action->list, &desc->head);
 131
 132         spin_unlock_irqrestore(&desc->lock, flags);
 133         return 0;
 134 }
 135
 136 static struct nmiaction *__free_nmi(unsigned int type, const char *name)
 137 {
 138         struct nmi_desc *desc = nmi_to_desc(type);
 139         struct nmiaction *n;
 140         unsigned long flags;
 141
 142         spin_lock_irqsave(&desc->lock, flags);
 143
 144         list_for_each_entry_rcu(n, &desc->head, list) {
 145                 /*
 146                  * the name passed in to describe the nmi handler
 147                  * is used as the lookup key
 148                  */
 149                 if (!strcmp(n->name, name)) {
 150                         WARN(in_nmi(),
 151                                 "Trying to free NMI (%s) from NMI context!\n", n->name);
 152                         list_del_rcu(&n->list);
 153                         break;
 154                 }
 155         }
 156
 157         spin_unlock_irqrestore(&desc->lock, flags);
 158         synchronize_rcu();
 159         return (n);
 160 }
 161
 162 int register_nmi_handler(unsigned int type, nmi_handler_t handler,
 163                         unsigned long nmiflags, const char *devname)
 164 {
 165         struct nmiaction *action;
 166         int retval = -ENOMEM;
 167
 168         if (!handler)
 169                 return -EINVAL;
 170
 171         action = kzalloc(sizeof(struct nmiaction), GFP_KERNEL);
 172         if (!action)
 173                 goto fail_action;
 174
 175         action->handler = handler;
 176         action->flags = nmiflags;
 177         action->name = kstrndup(devname, NMI_MAX_NAMELEN, GFP_KERNEL);
 178         if (!action->name)
 179                 goto fail_action_name;
 180
 181         retval = __setup_nmi(type, action);
 182
 183         if (retval)
 184                 goto fail_setup_nmi;
 185
 186         return retval;
 187
 188 fail_setup_nmi:
 189         kfree(action->name);
 190 fail_action_name:
 191         kfree(action);
 192 fail_action:
 193
 194         return retval;
 195 }
 196 EXPORT_SYMBOL_GPL(register_nmi_handler);
 197
 198 void unregister_nmi_handler(unsigned int type, const char *name)
 199 {
 200         struct nmiaction *a;
 201
 202         a = __free_nmi(type, name);
 203         if (a) {
 204                 kfree(a->name);
 205                 kfree(a);
 206         }
 207 }
 208
 209 EXPORT_SYMBOL_GPL(unregister_nmi_handler);
 210
 211 static notrace __kprobes void
 212 pci_serr_error(unsigned char reason, struct pt_regs *regs)
 213 {
 214         pr_emerg("NMI: PCI system error (SERR) for reason %02x on CPU %d.\n",
 215                  reason, smp_processor_id());
 216
 217         /*
 218          * On some machines, PCI SERR line is used to report memory
 219          * errors. EDAC makes use of it.
 220          */
 221 #if defined(CONFIG_EDAC)
 222         if (edac_handler_set()) {
 223                 edac_atomic_assert_error();
 224                 return;
 225         }
 226 #endif
 227
 228         if (panic_on_unrecovered_nmi)
 229                 panic("NMI: Not continuing");
 230
 231         pr_emerg("Dazed and confused, but trying to continue\n");
 232
 233         /* Clear and disable the PCI SERR error line. */
 234         reason = (reason & NMI_REASON_CLEAR_MASK) | NMI_REASON_CLEAR_SERR;
 235         outb(reason, NMI_REASON_PORT);
 236 }
 237
 238 static notrace __kprobes void
 239 io_check_error(unsigned char reason, struct pt_regs *regs)
 240 {
 241         unsigned long i;
 242
 243         pr_emerg(
 244         "NMI: IOCK error (debug interrupt?) for reason %02x on CPU %d.\n",
 245                  reason, smp_processor_id());
 246         show_registers(regs);
 247
 248         if (panic_on_io_nmi)
 249                 panic("NMI IOCK error: Not continuing");
 250
 251         /* Re-enable the IOCK line, wait for a few seconds */
 252         reason = (reason & NMI_REASON_CLEAR_MASK) | NMI_REASON_CLEAR_IOCHK;
 253         outb(reason, NMI_REASON_PORT);
 254
 255         i = 20000;
 256         while (--i) {
 257                 touch_nmi_watchdog();
 258                 udelay(100);
 259         }
 260
 261         reason &= ~NMI_REASON_CLEAR_IOCHK;
 262         outb(reason, NMI_REASON_PORT);
 263 }
 264
 265 static notrace __kprobes void
 266 unknown_nmi_error(unsigned char reason, struct pt_regs *regs)
 267 {
 268         int handled;
 269
 270         /*
 271          * Use 'false' as back-to-back NMIs are dealt with one level up.
 272          * Of course this makes having multiple 'unknown' handlers useless
 273          * as only the first one is ever run (unless it can actually determine
 274          * if it caused the NMI)
 275          */
 276         handled = nmi_handle(NMI_UNKNOWN, regs, false);
 277         if (handled) {
 278                 __this_cpu_add(nmi_stats.unknown, handled);
 279                 return;
 280         }
 281
 282         __this_cpu_add(nmi_stats.unknown, 1);
 283
 284 #ifdef CONFIG_MCA
 285         /*
 286          * Might actually be able to figure out what the guilty party
 287          * is:
 288          */
 289         if (MCA_bus) {
 290                 mca_handle_nmi();
 291                 return;
 292         }
 293 #endif
 294         pr_emerg("Uhhuh. NMI received for unknown reason %02x on CPU %d.\n",
 295                  reason, smp_processor_id());
 296
 297         pr_emerg("Do you have a strange power saving mode enabled?\n");
 298         if (unknown_nmi_panic || panic_on_unrecovered_nmi)
 299                 panic("NMI: Not continuing");
 300
 301         pr_emerg("Dazed and confused, but trying to continue\n");
 302 }
 303
 304 static DEFINE_PER_CPU(bool, swallow_nmi);
 305 static DEFINE_PER_CPU(unsigned long, last_nmi_rip);
 306
 307 static notrace __kprobes void default_do_nmi(struct pt_regs *regs)
 308 {
 309         unsigned char reason = 0;
 310         int handled;
 311         bool b2b = false;
 312
 313         /*
 314          * CPU-specific NMI must be processed before non-CPU-specific
 315          * NMI, otherwise we may lose it, because the CPU-specific
 316          * NMI can not be detected/processed on other CPUs.
 317          */
 318
 319         /*
 320          * Back-to-back NMIs are interesting because they can either
 321          * be two NMI or more than two NMIs (any thing over two is dropped
 322          * due to NMI being edge-triggered).  If this is the second half
 323          * of the back-to-back NMI, assume we dropped things and process
 324          * more handlers.  Otherwise reset the 'swallow' NMI behaviour
 325          */
 326         if (regs->ip == __this_cpu_read(last_nmi_rip))
 327                 b2b = true;
 328         else
 329                 __this_cpu_write(swallow_nmi, false);
 330
 331         __this_cpu_write(last_nmi_rip, regs->ip);
 332
 333         handled = nmi_handle(NMI_LOCAL, regs, b2b);
 334         __this_cpu_add(nmi_stats.normal, handled);
 335         if (handled) {
 336                 /*
 337                  * There are cases when a NMI handler handles multiple
 338                  * events in the current NMI.  One of these events may
 339                  * be queued for in the next NMI.  Because the event is
 340                  * already handled, the next NMI will result in an unknown
 341                  * NMI.  Instead lets flag this for a potential NMI to
 342                  * swallow.
 343                  */
 344                 if (handled > 1)
 345                         __this_cpu_write(swallow_nmi, true);
 346                 return;
 347         }
 348
 349         /* Non-CPU-specific NMI: NMI sources can be processed on any CPU */
 350         raw_spin_lock(&nmi_reason_lock);
 351         reason = get_nmi_reason();
 352
 353         if (reason & NMI_REASON_MASK) {
 354                 if (reason & NMI_REASON_SERR)
 355                         pci_serr_error(reason, regs);
 356                 else if (reason & NMI_REASON_IOCHK)
 357                         io_check_error(reason, regs);
 358 #ifdef CONFIG_X86_32
 359                 /*
 360                  * Reassert NMI in case it became active
 361                  * meanwhile as it's edge-triggered:
 362                  */
 363                 reassert_nmi();
 364 #endif
 365                 __this_cpu_add(nmi_stats.external, 1);
 366                 raw_spin_unlock(&nmi_reason_lock);
 367                 return;
 368         }
 369         raw_spin_unlock(&nmi_reason_lock);
 370
 371         /*
 372          * Only one NMI can be latched at a time.  To handle
 373          * this we may process multiple nmi handlers at once to
 374          * cover the case where an NMI is dropped.  The downside
 375          * to this approach is we may process an NMI prematurely,
 376          * while its real NMI is sitting latched.  This will cause
 377          * an unknown NMI on the next run of the NMI processing.
 378          *
 379          * We tried to flag that condition above, by setting the
 380          * swallow_nmi flag when we process more than one event.
 381          * This condition is also only present on the second half
 382          * of a back-to-back NMI, so we flag that condition too.
 383          *
 384          * If both are true, we assume we already processed this
 385          * NMI previously and we swallow it.  Otherwise we reset
 386          * the logic.
 387          *
 388          * There are scenarios where we may accidentally swallow
 389          * a 'real' unknown NMI.  For example, while processing
 390          * a perf NMI another perf NMI comes in along with a
 391          * 'real' unknown NMI.  These two NMIs get combined into
 392          * one (as descibed above).  When the next NMI gets
 393          * processed, it will be flagged by perf as handled, but
 394          * noone will know that there was a 'real' unknown NMI sent
 395          * also.  As a result it gets swallowed.  Or if the first
 396          * perf NMI returns two events handled then the second
 397          * NMI will get eaten by the logic below, again losing a
 398          * 'real' unknown NMI.  But this is the best we can do
 399          * for now.
 400          */
 401         if (b2b && __this_cpu_read(swallow_nmi))
 402                 __this_cpu_add(nmi_stats.swallow, 1);
 403         else
 404                 unknown_nmi_error(reason, regs);
 405 }
 406
 407 dotraplinkage notrace __kprobes void
 408 do_nmi(struct pt_regs *regs, long error_code)
 409 {
 410         nmi_enter();
 411
 412         inc_irq_stat(__nmi_count);
 413
 414         if (!ignore_nmis)
 415                 default_do_nmi(regs);
 416
 417         nmi_exit();
 418 }
 419
 420 void stop_nmi(void)
 421 {
 422         ignore_nmis++;
 423 }
 424
 425 void restart_nmi(void)
 426 {
 427         ignore_nmis--;
 428 }
 429
 430 /* reset the back-to-back NMI logic */
 431 void local_touch_nmi(void)
 432 {
 433         __this_cpu_write(last_nmi_rip, 0);
 434 }