Linux 3.8-rc7
[cris-mirror.git] / arch / x86 / kernel / nmi.c
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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.
6 * Pentium III FXSR, SSE support
7 * Gareth Hughes <gareth@valinux.com>, May 2000
8 */
11 * Handle hardware traps and faults.
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>
22 #if defined(CONFIG_EDAC)
23 #include <linux/edac.h>
24 #endif
26 #include <linux/atomic.h>
27 #include <asm/traps.h>
28 #include <asm/mach_traps.h>
29 #include <asm/nmi.h>
30 #include <asm/x86_init.h>
32 struct nmi_desc {
33 spinlock_t lock;
34 struct list_head head;
37 static struct nmi_desc nmi_desc[NMI_MAX] =
40 .lock = __SPIN_LOCK_UNLOCKED(&nmi_desc[0].lock),
41 .head = LIST_HEAD_INIT(nmi_desc[0].head),
44 .lock = __SPIN_LOCK_UNLOCKED(&nmi_desc[1].lock),
45 .head = LIST_HEAD_INIT(nmi_desc[1].head),
48 .lock = __SPIN_LOCK_UNLOCKED(&nmi_desc[2].lock),
49 .head = LIST_HEAD_INIT(nmi_desc[2].head),
52 .lock = __SPIN_LOCK_UNLOCKED(&nmi_desc[3].lock),
53 .head = LIST_HEAD_INIT(nmi_desc[3].head),
58 struct nmi_stats {
59 unsigned int normal;
60 unsigned int unknown;
61 unsigned int external;
62 unsigned int swallow;
65 static DEFINE_PER_CPU(struct nmi_stats, nmi_stats);
67 static int ignore_nmis;
69 int unknown_nmi_panic;
71 * Prevent NMI reason port (0x61) being accessed simultaneously, can
72 * only be used in NMI handler.
74 static DEFINE_RAW_SPINLOCK(nmi_reason_lock);
76 static int __init setup_unknown_nmi_panic(char *str)
78 unknown_nmi_panic = 1;
79 return 1;
81 __setup("unknown_nmi_panic", setup_unknown_nmi_panic);
83 #define nmi_to_desc(type) (&nmi_desc[type])
85 static int __kprobes nmi_handle(unsigned int type, struct pt_regs *regs, bool b2b)
87 struct nmi_desc *desc = nmi_to_desc(type);
88 struct nmiaction *a;
89 int handled=0;
91 rcu_read_lock();
94 * NMIs are edge-triggered, which means if you have enough
95 * of them concurrently, you can lose some because only one
96 * can be latched at any given time. Walk the whole list
97 * to handle those situations.
99 list_for_each_entry_rcu(a, &desc->head, list)
100 handled += a->handler(type, regs);
102 rcu_read_unlock();
104 /* return total number of NMI events handled */
105 return handled;
108 int __register_nmi_handler(unsigned int type, struct nmiaction *action)
110 struct nmi_desc *desc = nmi_to_desc(type);
111 unsigned long flags;
113 if (!action->handler)
114 return -EINVAL;
116 spin_lock_irqsave(&desc->lock, flags);
119 * most handlers of type NMI_UNKNOWN never return because
120 * they just assume the NMI is theirs. Just a sanity check
121 * to manage expectations
123 WARN_ON_ONCE(type == NMI_UNKNOWN && !list_empty(&desc->head));
124 WARN_ON_ONCE(type == NMI_SERR && !list_empty(&desc->head));
125 WARN_ON_ONCE(type == NMI_IO_CHECK && !list_empty(&desc->head));
128 * some handlers need to be executed first otherwise a fake
129 * event confuses some handlers (kdump uses this flag)
131 if (action->flags & NMI_FLAG_FIRST)
132 list_add_rcu(&action->list, &desc->head);
133 else
134 list_add_tail_rcu(&action->list, &desc->head);
136 spin_unlock_irqrestore(&desc->lock, flags);
137 return 0;
139 EXPORT_SYMBOL(__register_nmi_handler);
141 void unregister_nmi_handler(unsigned int type, const char *name)
143 struct nmi_desc *desc = nmi_to_desc(type);
144 struct nmiaction *n;
145 unsigned long flags;
147 spin_lock_irqsave(&desc->lock, flags);
149 list_for_each_entry_rcu(n, &desc->head, list) {
151 * the name passed in to describe the nmi handler
152 * is used as the lookup key
154 if (!strcmp(n->name, name)) {
155 WARN(in_nmi(),
156 "Trying to free NMI (%s) from NMI context!\n", n->name);
157 list_del_rcu(&n->list);
158 break;
162 spin_unlock_irqrestore(&desc->lock, flags);
163 synchronize_rcu();
165 EXPORT_SYMBOL_GPL(unregister_nmi_handler);
167 static __kprobes void
168 pci_serr_error(unsigned char reason, struct pt_regs *regs)
170 /* check to see if anyone registered against these types of errors */
171 if (nmi_handle(NMI_SERR, regs, false))
172 return;
174 pr_emerg("NMI: PCI system error (SERR) for reason %02x on CPU %d.\n",
175 reason, smp_processor_id());
178 * On some machines, PCI SERR line is used to report memory
179 * errors. EDAC makes use of it.
181 #if defined(CONFIG_EDAC)
182 if (edac_handler_set()) {
183 edac_atomic_assert_error();
184 return;
186 #endif
188 if (panic_on_unrecovered_nmi)
189 panic("NMI: Not continuing");
191 pr_emerg("Dazed and confused, but trying to continue\n");
193 /* Clear and disable the PCI SERR error line. */
194 reason = (reason & NMI_REASON_CLEAR_MASK) | NMI_REASON_CLEAR_SERR;
195 outb(reason, NMI_REASON_PORT);
198 static __kprobes void
199 io_check_error(unsigned char reason, struct pt_regs *regs)
201 unsigned long i;
203 /* check to see if anyone registered against these types of errors */
204 if (nmi_handle(NMI_IO_CHECK, regs, false))
205 return;
207 pr_emerg(
208 "NMI: IOCK error (debug interrupt?) for reason %02x on CPU %d.\n",
209 reason, smp_processor_id());
210 show_regs(regs);
212 if (panic_on_io_nmi)
213 panic("NMI IOCK error: Not continuing");
215 /* Re-enable the IOCK line, wait for a few seconds */
216 reason = (reason & NMI_REASON_CLEAR_MASK) | NMI_REASON_CLEAR_IOCHK;
217 outb(reason, NMI_REASON_PORT);
219 i = 20000;
220 while (--i) {
221 touch_nmi_watchdog();
222 udelay(100);
225 reason &= ~NMI_REASON_CLEAR_IOCHK;
226 outb(reason, NMI_REASON_PORT);
229 static __kprobes void
230 unknown_nmi_error(unsigned char reason, struct pt_regs *regs)
232 int handled;
235 * Use 'false' as back-to-back NMIs are dealt with one level up.
236 * Of course this makes having multiple 'unknown' handlers useless
237 * as only the first one is ever run (unless it can actually determine
238 * if it caused the NMI)
240 handled = nmi_handle(NMI_UNKNOWN, regs, false);
241 if (handled) {
242 __this_cpu_add(nmi_stats.unknown, handled);
243 return;
246 __this_cpu_add(nmi_stats.unknown, 1);
248 pr_emerg("Uhhuh. NMI received for unknown reason %02x on CPU %d.\n",
249 reason, smp_processor_id());
251 pr_emerg("Do you have a strange power saving mode enabled?\n");
252 if (unknown_nmi_panic || panic_on_unrecovered_nmi)
253 panic("NMI: Not continuing");
255 pr_emerg("Dazed and confused, but trying to continue\n");
258 static DEFINE_PER_CPU(bool, swallow_nmi);
259 static DEFINE_PER_CPU(unsigned long, last_nmi_rip);
261 static __kprobes void default_do_nmi(struct pt_regs *regs)
263 unsigned char reason = 0;
264 int handled;
265 bool b2b = false;
268 * CPU-specific NMI must be processed before non-CPU-specific
269 * NMI, otherwise we may lose it, because the CPU-specific
270 * NMI can not be detected/processed on other CPUs.
274 * Back-to-back NMIs are interesting because they can either
275 * be two NMI or more than two NMIs (any thing over two is dropped
276 * due to NMI being edge-triggered). If this is the second half
277 * of the back-to-back NMI, assume we dropped things and process
278 * more handlers. Otherwise reset the 'swallow' NMI behaviour
280 if (regs->ip == __this_cpu_read(last_nmi_rip))
281 b2b = true;
282 else
283 __this_cpu_write(swallow_nmi, false);
285 __this_cpu_write(last_nmi_rip, regs->ip);
287 handled = nmi_handle(NMI_LOCAL, regs, b2b);
288 __this_cpu_add(nmi_stats.normal, handled);
289 if (handled) {
291 * There are cases when a NMI handler handles multiple
292 * events in the current NMI. One of these events may
293 * be queued for in the next NMI. Because the event is
294 * already handled, the next NMI will result in an unknown
295 * NMI. Instead lets flag this for a potential NMI to
296 * swallow.
298 if (handled > 1)
299 __this_cpu_write(swallow_nmi, true);
300 return;
303 /* Non-CPU-specific NMI: NMI sources can be processed on any CPU */
304 raw_spin_lock(&nmi_reason_lock);
305 reason = x86_platform.get_nmi_reason();
307 if (reason & NMI_REASON_MASK) {
308 if (reason & NMI_REASON_SERR)
309 pci_serr_error(reason, regs);
310 else if (reason & NMI_REASON_IOCHK)
311 io_check_error(reason, regs);
312 #ifdef CONFIG_X86_32
314 * Reassert NMI in case it became active
315 * meanwhile as it's edge-triggered:
317 reassert_nmi();
318 #endif
319 __this_cpu_add(nmi_stats.external, 1);
320 raw_spin_unlock(&nmi_reason_lock);
321 return;
323 raw_spin_unlock(&nmi_reason_lock);
326 * Only one NMI can be latched at a time. To handle
327 * this we may process multiple nmi handlers at once to
328 * cover the case where an NMI is dropped. The downside
329 * to this approach is we may process an NMI prematurely,
330 * while its real NMI is sitting latched. This will cause
331 * an unknown NMI on the next run of the NMI processing.
333 * We tried to flag that condition above, by setting the
334 * swallow_nmi flag when we process more than one event.
335 * This condition is also only present on the second half
336 * of a back-to-back NMI, so we flag that condition too.
338 * If both are true, we assume we already processed this
339 * NMI previously and we swallow it. Otherwise we reset
340 * the logic.
342 * There are scenarios where we may accidentally swallow
343 * a 'real' unknown NMI. For example, while processing
344 * a perf NMI another perf NMI comes in along with a
345 * 'real' unknown NMI. These two NMIs get combined into
346 * one (as descibed above). When the next NMI gets
347 * processed, it will be flagged by perf as handled, but
348 * noone will know that there was a 'real' unknown NMI sent
349 * also. As a result it gets swallowed. Or if the first
350 * perf NMI returns two events handled then the second
351 * NMI will get eaten by the logic below, again losing a
352 * 'real' unknown NMI. But this is the best we can do
353 * for now.
355 if (b2b && __this_cpu_read(swallow_nmi))
356 __this_cpu_add(nmi_stats.swallow, 1);
357 else
358 unknown_nmi_error(reason, regs);
362 * NMIs can hit breakpoints which will cause it to lose its
363 * NMI context with the CPU when the breakpoint does an iret.
365 #ifdef CONFIG_X86_32
367 * For i386, NMIs use the same stack as the kernel, and we can
368 * add a workaround to the iret problem in C (preventing nested
369 * NMIs if an NMI takes a trap). Simply have 3 states the NMI
370 * can be in:
372 * 1) not running
373 * 2) executing
374 * 3) latched
376 * When no NMI is in progress, it is in the "not running" state.
377 * When an NMI comes in, it goes into the "executing" state.
378 * Normally, if another NMI is triggered, it does not interrupt
379 * the running NMI and the HW will simply latch it so that when
380 * the first NMI finishes, it will restart the second NMI.
381 * (Note, the latch is binary, thus multiple NMIs triggering,
382 * when one is running, are ignored. Only one NMI is restarted.)
384 * If an NMI hits a breakpoint that executes an iret, another
385 * NMI can preempt it. We do not want to allow this new NMI
386 * to run, but we want to execute it when the first one finishes.
387 * We set the state to "latched", and the exit of the first NMI will
388 * perform a dec_return, if the result is zero (NOT_RUNNING), then
389 * it will simply exit the NMI handler. If not, the dec_return
390 * would have set the state to NMI_EXECUTING (what we want it to
391 * be when we are running). In this case, we simply jump back
392 * to rerun the NMI handler again, and restart the 'latched' NMI.
394 * No trap (breakpoint or page fault) should be hit before nmi_restart,
395 * thus there is no race between the first check of state for NOT_RUNNING
396 * and setting it to NMI_EXECUTING. The HW will prevent nested NMIs
397 * at this point.
399 * In case the NMI takes a page fault, we need to save off the CR2
400 * because the NMI could have preempted another page fault and corrupt
401 * the CR2 that is about to be read. As nested NMIs must be restarted
402 * and they can not take breakpoints or page faults, the update of the
403 * CR2 must be done before converting the nmi state back to NOT_RUNNING.
404 * Otherwise, there would be a race of another nested NMI coming in
405 * after setting state to NOT_RUNNING but before updating the nmi_cr2.
407 enum nmi_states {
408 NMI_NOT_RUNNING = 0,
409 NMI_EXECUTING,
410 NMI_LATCHED,
412 static DEFINE_PER_CPU(enum nmi_states, nmi_state);
413 static DEFINE_PER_CPU(unsigned long, nmi_cr2);
415 #define nmi_nesting_preprocess(regs) \
416 do { \
417 if (this_cpu_read(nmi_state) != NMI_NOT_RUNNING) { \
418 this_cpu_write(nmi_state, NMI_LATCHED); \
419 return; \
421 this_cpu_write(nmi_state, NMI_EXECUTING); \
422 this_cpu_write(nmi_cr2, read_cr2()); \
423 } while (0); \
424 nmi_restart:
426 #define nmi_nesting_postprocess() \
427 do { \
428 if (unlikely(this_cpu_read(nmi_cr2) != read_cr2())) \
429 write_cr2(this_cpu_read(nmi_cr2)); \
430 if (this_cpu_dec_return(nmi_state)) \
431 goto nmi_restart; \
432 } while (0)
433 #else /* x86_64 */
435 * In x86_64 things are a bit more difficult. This has the same problem
436 * where an NMI hitting a breakpoint that calls iret will remove the
437 * NMI context, allowing a nested NMI to enter. What makes this more
438 * difficult is that both NMIs and breakpoints have their own stack.
439 * When a new NMI or breakpoint is executed, the stack is set to a fixed
440 * point. If an NMI is nested, it will have its stack set at that same
441 * fixed address that the first NMI had, and will start corrupting the
442 * stack. This is handled in entry_64.S, but the same problem exists with
443 * the breakpoint stack.
445 * If a breakpoint is being processed, and the debug stack is being used,
446 * if an NMI comes in and also hits a breakpoint, the stack pointer
447 * will be set to the same fixed address as the breakpoint that was
448 * interrupted, causing that stack to be corrupted. To handle this case,
449 * check if the stack that was interrupted is the debug stack, and if
450 * so, change the IDT so that new breakpoints will use the current stack
451 * and not switch to the fixed address. On return of the NMI, switch back
452 * to the original IDT.
454 static DEFINE_PER_CPU(int, update_debug_stack);
456 static inline void nmi_nesting_preprocess(struct pt_regs *regs)
459 * If we interrupted a breakpoint, it is possible that
460 * the nmi handler will have breakpoints too. We need to
461 * change the IDT such that breakpoints that happen here
462 * continue to use the NMI stack.
464 if (unlikely(is_debug_stack(regs->sp))) {
465 debug_stack_set_zero();
466 this_cpu_write(update_debug_stack, 1);
470 static inline void nmi_nesting_postprocess(void)
472 if (unlikely(this_cpu_read(update_debug_stack))) {
473 debug_stack_reset();
474 this_cpu_write(update_debug_stack, 0);
477 #endif
479 dotraplinkage notrace __kprobes void
480 do_nmi(struct pt_regs *regs, long error_code)
482 nmi_nesting_preprocess(regs);
484 nmi_enter();
486 inc_irq_stat(__nmi_count);
488 if (!ignore_nmis)
489 default_do_nmi(regs);
491 nmi_exit();
493 /* On i386, may loop back to preprocess */
494 nmi_nesting_postprocess();
497 void stop_nmi(void)
499 ignore_nmis++;
502 void restart_nmi(void)
504 ignore_nmis--;
507 /* reset the back-to-back NMI logic */
508 void local_touch_nmi(void)
510 __this_cpu_write(last_nmi_rip, 0);