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Don Zickus1d489222011-09-30 15:06:19 -04001/*
2 * Copyright (C) 1991, 1992 Linus Torvalds
3 * Copyright (C) 2000, 2001, 2002 Andi Kleen, SuSE Labs
Don Zickus9c48f1c2011-09-30 15:06:21 -04004 * Copyright (C) 2011 Don Zickus Red Hat, Inc.
Don Zickus1d489222011-09-30 15:06:19 -04005 *
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>
Dave Hansen2ab004562013-06-21 08:51:35 -070017#include <linux/debugfs.h>
Don Zickusc9126b22011-09-30 15:06:20 -040018#include <linux/delay.h>
19#include <linux/hardirq.h>
Arnd Bergmannc361db52016-06-06 16:09:52 +020020#include <linux/ratelimit.h>
Don Zickusc9126b22011-09-30 15:06:20 -040021#include <linux/slab.h>
Paul Gortmaker69c60c82011-05-26 12:22:53 -040022#include <linux/export.h>
Don Zickus1d489222011-09-30 15:06:19 -040023
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>
Don Zickusc9126b22011-09-30 15:06:20 -040031#include <asm/nmi.h>
Mathias Nyman6fd36ba2011-11-10 13:45:24 +000032#include <asm/x86_init.h>
Hidehiro Kawaib279d672015-12-14 11:19:13 +010033#include <asm/reboot.h>
Kostenzer Felix8e2a7f52016-03-06 23:20:06 +010034#include <asm/cache.h>
Don Zickusc9126b22011-09-30 15:06:20 -040035
Dave Hansen0c4df022013-06-21 08:51:38 -070036#define CREATE_TRACE_POINTS
37#include <trace/events/nmi.h>
38
Don Zickusc9126b22011-09-30 15:06:20 -040039struct nmi_desc {
40 spinlock_t lock;
41 struct list_head head;
42};
43
44static struct nmi_desc nmi_desc[NMI_MAX] =
45{
46 {
47 .lock = __SPIN_LOCK_UNLOCKED(&nmi_desc[0].lock),
48 .head = LIST_HEAD_INIT(nmi_desc[0].head),
49 },
50 {
51 .lock = __SPIN_LOCK_UNLOCKED(&nmi_desc[1].lock),
52 .head = LIST_HEAD_INIT(nmi_desc[1].head),
53 },
Don Zickus553222f2012-03-29 16:11:16 -040054 {
55 .lock = __SPIN_LOCK_UNLOCKED(&nmi_desc[2].lock),
56 .head = LIST_HEAD_INIT(nmi_desc[2].head),
57 },
58 {
59 .lock = __SPIN_LOCK_UNLOCKED(&nmi_desc[3].lock),
60 .head = LIST_HEAD_INIT(nmi_desc[3].head),
61 },
Don Zickusc9126b22011-09-30 15:06:20 -040062
63};
Don Zickus1d489222011-09-30 15:06:19 -040064
Don Zickusefc3aac2011-09-30 15:06:23 -040065struct nmi_stats {
66 unsigned int normal;
67 unsigned int unknown;
68 unsigned int external;
69 unsigned int swallow;
70};
71
72static DEFINE_PER_CPU(struct nmi_stats, nmi_stats);
73
Kostenzer Felix8e2a7f52016-03-06 23:20:06 +010074static int ignore_nmis __read_mostly;
Don Zickus1d489222011-09-30 15:06:19 -040075
76int unknown_nmi_panic;
77/*
78 * Prevent NMI reason port (0x61) being accessed simultaneously, can
79 * only be used in NMI handler.
80 */
81static DEFINE_RAW_SPINLOCK(nmi_reason_lock);
82
83static int __init setup_unknown_nmi_panic(char *str)
84{
85 unknown_nmi_panic = 1;
86 return 1;
87}
88__setup("unknown_nmi_panic", setup_unknown_nmi_panic);
89
Don Zickusc9126b22011-09-30 15:06:20 -040090#define nmi_to_desc(type) (&nmi_desc[type])
91
Dave Hansen2ab004562013-06-21 08:51:35 -070092static u64 nmi_longest_ns = 1 * NSEC_PER_MSEC;
Peter Zijlstrae90c7852014-02-03 18:02:09 +010093
Dave Hansen2ab004562013-06-21 08:51:35 -070094static int __init nmi_warning_debugfs(void)
95{
96 debugfs_create_u64("nmi_longest_ns", 0644,
97 arch_debugfs_dir, &nmi_longest_ns);
98 return 0;
99}
100fs_initcall(nmi_warning_debugfs);
101
Peter Zijlstrae90c7852014-02-03 18:02:09 +0100102static void nmi_max_handler(struct irq_work *w)
103{
104 struct nmiaction *a = container_of(w, struct nmiaction, irq_work);
105 int remainder_ns, decimal_msecs;
106 u64 whole_msecs = ACCESS_ONCE(a->max_duration);
107
108 remainder_ns = do_div(whole_msecs, (1000 * 1000));
109 decimal_msecs = remainder_ns / 1000;
110
111 printk_ratelimited(KERN_INFO
112 "INFO: NMI handler (%ps) took too long to run: %lld.%03d msecs\n",
113 a->handler, whole_msecs, decimal_msecs);
114}
115
Andy Lutomirskibf9f2ee2015-07-20 11:52:23 -0700116static int nmi_handle(unsigned int type, struct pt_regs *regs)
Don Zickusc9126b22011-09-30 15:06:20 -0400117{
118 struct nmi_desc *desc = nmi_to_desc(type);
119 struct nmiaction *a;
120 int handled=0;
121
122 rcu_read_lock();
123
124 /*
125 * NMIs are edge-triggered, which means if you have enough
126 * of them concurrently, you can lose some because only one
127 * can be latched at any given time. Walk the whole list
128 * to handle those situations.
129 */
Dave Hansen2ab004562013-06-21 08:51:35 -0700130 list_for_each_entry_rcu(a, &desc->head, list) {
Peter Zijlstrae90c7852014-02-03 18:02:09 +0100131 int thishandled;
132 u64 delta;
Dave Hansen2ab004562013-06-21 08:51:35 -0700133
Peter Zijlstrae90c7852014-02-03 18:02:09 +0100134 delta = sched_clock();
Dave Hansen0c4df022013-06-21 08:51:38 -0700135 thishandled = a->handler(type, regs);
136 handled += thishandled;
Peter Zijlstrae90c7852014-02-03 18:02:09 +0100137 delta = sched_clock() - delta;
Dave Hansen0c4df022013-06-21 08:51:38 -0700138 trace_nmi_handler(a->handler, (int)delta, thishandled);
Dave Hansen2ab004562013-06-21 08:51:35 -0700139
Peter Zijlstrae90c7852014-02-03 18:02:09 +0100140 if (delta < nmi_longest_ns || delta < a->max_duration)
Dave Hansen2ab004562013-06-21 08:51:35 -0700141 continue;
142
Peter Zijlstrae90c7852014-02-03 18:02:09 +0100143 a->max_duration = delta;
144 irq_work_queue(&a->irq_work);
Dave Hansen2ab004562013-06-21 08:51:35 -0700145 }
Don Zickusc9126b22011-09-30 15:06:20 -0400146
Don Zickusc9126b22011-09-30 15:06:20 -0400147 rcu_read_unlock();
148
149 /* return total number of NMI events handled */
150 return handled;
151}
Masami Hiramatsu93266382014-04-17 17:18:14 +0900152NOKPROBE_SYMBOL(nmi_handle);
Don Zickusc9126b22011-09-30 15:06:20 -0400153
Li Zhong72b3fb22012-03-29 16:11:17 -0400154int __register_nmi_handler(unsigned int type, struct nmiaction *action)
Don Zickusc9126b22011-09-30 15:06:20 -0400155{
156 struct nmi_desc *desc = nmi_to_desc(type);
157 unsigned long flags;
158
Li Zhong72b3fb22012-03-29 16:11:17 -0400159 if (!action->handler)
160 return -EINVAL;
161
Peter Zijlstrae90c7852014-02-03 18:02:09 +0100162 init_irq_work(&action->irq_work, nmi_max_handler);
163
Don Zickusc9126b22011-09-30 15:06:20 -0400164 spin_lock_irqsave(&desc->lock, flags);
165
166 /*
Don Zickusb227e232011-09-30 15:06:22 -0400167 * most handlers of type NMI_UNKNOWN never return because
168 * they just assume the NMI is theirs. Just a sanity check
169 * to manage expectations
170 */
171 WARN_ON_ONCE(type == NMI_UNKNOWN && !list_empty(&desc->head));
Don Zickus553222f2012-03-29 16:11:16 -0400172 WARN_ON_ONCE(type == NMI_SERR && !list_empty(&desc->head));
173 WARN_ON_ONCE(type == NMI_IO_CHECK && !list_empty(&desc->head));
Don Zickusb227e232011-09-30 15:06:22 -0400174
175 /*
Don Zickusc9126b22011-09-30 15:06:20 -0400176 * some handlers need to be executed first otherwise a fake
177 * event confuses some handlers (kdump uses this flag)
178 */
179 if (action->flags & NMI_FLAG_FIRST)
180 list_add_rcu(&action->list, &desc->head);
181 else
182 list_add_tail_rcu(&action->list, &desc->head);
183
184 spin_unlock_irqrestore(&desc->lock, flags);
185 return 0;
186}
Li Zhong72b3fb22012-03-29 16:11:17 -0400187EXPORT_SYMBOL(__register_nmi_handler);
Don Zickusc9126b22011-09-30 15:06:20 -0400188
Li Zhong72b3fb22012-03-29 16:11:17 -0400189void unregister_nmi_handler(unsigned int type, const char *name)
Don Zickusc9126b22011-09-30 15:06:20 -0400190{
191 struct nmi_desc *desc = nmi_to_desc(type);
192 struct nmiaction *n;
193 unsigned long flags;
194
195 spin_lock_irqsave(&desc->lock, flags);
196
197 list_for_each_entry_rcu(n, &desc->head, list) {
198 /*
199 * the name passed in to describe the nmi handler
200 * is used as the lookup key
201 */
202 if (!strcmp(n->name, name)) {
203 WARN(in_nmi(),
204 "Trying to free NMI (%s) from NMI context!\n", n->name);
205 list_del_rcu(&n->list);
206 break;
207 }
208 }
209
210 spin_unlock_irqrestore(&desc->lock, flags);
211 synchronize_rcu();
Don Zickusc9126b22011-09-30 15:06:20 -0400212}
Don Zickusc9126b22011-09-30 15:06:20 -0400213EXPORT_SYMBOL_GPL(unregister_nmi_handler);
214
Masami Hiramatsu93266382014-04-17 17:18:14 +0900215static void
Don Zickus1d489222011-09-30 15:06:19 -0400216pci_serr_error(unsigned char reason, struct pt_regs *regs)
217{
Don Zickus553222f2012-03-29 16:11:16 -0400218 /* check to see if anyone registered against these types of errors */
Andy Lutomirskibf9f2ee2015-07-20 11:52:23 -0700219 if (nmi_handle(NMI_SERR, regs))
Don Zickus553222f2012-03-29 16:11:16 -0400220 return;
221
Don Zickus1d489222011-09-30 15:06:19 -0400222 pr_emerg("NMI: PCI system error (SERR) for reason %02x on CPU %d.\n",
223 reason, smp_processor_id());
224
225 /*
226 * On some machines, PCI SERR line is used to report memory
227 * errors. EDAC makes use of it.
228 */
229#if defined(CONFIG_EDAC)
230 if (edac_handler_set()) {
231 edac_atomic_assert_error();
232 return;
233 }
234#endif
235
236 if (panic_on_unrecovered_nmi)
Hidehiro Kawai58c56612015-12-14 11:19:10 +0100237 nmi_panic(regs, "NMI: Not continuing");
Don Zickus1d489222011-09-30 15:06:19 -0400238
239 pr_emerg("Dazed and confused, but trying to continue\n");
240
241 /* Clear and disable the PCI SERR error line. */
242 reason = (reason & NMI_REASON_CLEAR_MASK) | NMI_REASON_CLEAR_SERR;
243 outb(reason, NMI_REASON_PORT);
244}
Masami Hiramatsu93266382014-04-17 17:18:14 +0900245NOKPROBE_SYMBOL(pci_serr_error);
Don Zickus1d489222011-09-30 15:06:19 -0400246
Masami Hiramatsu93266382014-04-17 17:18:14 +0900247static void
Don Zickus1d489222011-09-30 15:06:19 -0400248io_check_error(unsigned char reason, struct pt_regs *regs)
249{
250 unsigned long i;
251
Don Zickus553222f2012-03-29 16:11:16 -0400252 /* check to see if anyone registered against these types of errors */
Andy Lutomirskibf9f2ee2015-07-20 11:52:23 -0700253 if (nmi_handle(NMI_IO_CHECK, regs))
Don Zickus553222f2012-03-29 16:11:16 -0400254 return;
255
Don Zickus1d489222011-09-30 15:06:19 -0400256 pr_emerg(
257 "NMI: IOCK error (debug interrupt?) for reason %02x on CPU %d.\n",
258 reason, smp_processor_id());
Jan Beulich57da8b92012-05-09 08:47:37 +0100259 show_regs(regs);
Don Zickus1d489222011-09-30 15:06:19 -0400260
Hidehiro Kawai1717f202015-12-14 11:19:09 +0100261 if (panic_on_io_nmi) {
Hidehiro Kawai58c56612015-12-14 11:19:10 +0100262 nmi_panic(regs, "NMI IOCK error: Not continuing");
Hidehiro Kawai1717f202015-12-14 11:19:09 +0100263
264 /*
265 * If we end up here, it means we have received an NMI while
266 * processing panic(). Simply return without delaying and
267 * re-enabling NMIs.
268 */
269 return;
270 }
Don Zickus1d489222011-09-30 15:06:19 -0400271
272 /* Re-enable the IOCK line, wait for a few seconds */
273 reason = (reason & NMI_REASON_CLEAR_MASK) | NMI_REASON_CLEAR_IOCHK;
274 outb(reason, NMI_REASON_PORT);
275
276 i = 20000;
277 while (--i) {
278 touch_nmi_watchdog();
279 udelay(100);
280 }
281
282 reason &= ~NMI_REASON_CLEAR_IOCHK;
283 outb(reason, NMI_REASON_PORT);
284}
Masami Hiramatsu93266382014-04-17 17:18:14 +0900285NOKPROBE_SYMBOL(io_check_error);
Don Zickus1d489222011-09-30 15:06:19 -0400286
Masami Hiramatsu93266382014-04-17 17:18:14 +0900287static void
Don Zickus1d489222011-09-30 15:06:19 -0400288unknown_nmi_error(unsigned char reason, struct pt_regs *regs)
289{
Don Zickus9c48f1c2011-09-30 15:06:21 -0400290 int handled;
291
Don Zickusb227e232011-09-30 15:06:22 -0400292 /*
293 * Use 'false' as back-to-back NMIs are dealt with one level up.
294 * Of course this makes having multiple 'unknown' handlers useless
295 * as only the first one is ever run (unless it can actually determine
296 * if it caused the NMI)
297 */
Andy Lutomirskibf9f2ee2015-07-20 11:52:23 -0700298 handled = nmi_handle(NMI_UNKNOWN, regs);
Don Zickusefc3aac2011-09-30 15:06:23 -0400299 if (handled) {
300 __this_cpu_add(nmi_stats.unknown, handled);
Don Zickus1d489222011-09-30 15:06:19 -0400301 return;
Don Zickusefc3aac2011-09-30 15:06:23 -0400302 }
303
304 __this_cpu_add(nmi_stats.unknown, 1);
305
Don Zickus1d489222011-09-30 15:06:19 -0400306 pr_emerg("Uhhuh. NMI received for unknown reason %02x on CPU %d.\n",
307 reason, smp_processor_id());
308
309 pr_emerg("Do you have a strange power saving mode enabled?\n");
310 if (unknown_nmi_panic || panic_on_unrecovered_nmi)
Hidehiro Kawai58c56612015-12-14 11:19:10 +0100311 nmi_panic(regs, "NMI: Not continuing");
Don Zickus1d489222011-09-30 15:06:19 -0400312
313 pr_emerg("Dazed and confused, but trying to continue\n");
314}
Masami Hiramatsu93266382014-04-17 17:18:14 +0900315NOKPROBE_SYMBOL(unknown_nmi_error);
Don Zickus1d489222011-09-30 15:06:19 -0400316
Don Zickusb227e232011-09-30 15:06:22 -0400317static DEFINE_PER_CPU(bool, swallow_nmi);
318static DEFINE_PER_CPU(unsigned long, last_nmi_rip);
319
Masami Hiramatsu93266382014-04-17 17:18:14 +0900320static void default_do_nmi(struct pt_regs *regs)
Don Zickus1d489222011-09-30 15:06:19 -0400321{
322 unsigned char reason = 0;
Don Zickus9c48f1c2011-09-30 15:06:21 -0400323 int handled;
Don Zickusb227e232011-09-30 15:06:22 -0400324 bool b2b = false;
Don Zickus1d489222011-09-30 15:06:19 -0400325
326 /*
327 * CPU-specific NMI must be processed before non-CPU-specific
328 * NMI, otherwise we may lose it, because the CPU-specific
329 * NMI can not be detected/processed on other CPUs.
330 */
Don Zickusb227e232011-09-30 15:06:22 -0400331
332 /*
333 * Back-to-back NMIs are interesting because they can either
334 * be two NMI or more than two NMIs (any thing over two is dropped
335 * due to NMI being edge-triggered). If this is the second half
336 * of the back-to-back NMI, assume we dropped things and process
337 * more handlers. Otherwise reset the 'swallow' NMI behaviour
338 */
339 if (regs->ip == __this_cpu_read(last_nmi_rip))
340 b2b = true;
341 else
342 __this_cpu_write(swallow_nmi, false);
343
344 __this_cpu_write(last_nmi_rip, regs->ip);
345
Andy Lutomirskibf9f2ee2015-07-20 11:52:23 -0700346 handled = nmi_handle(NMI_LOCAL, regs);
Don Zickusefc3aac2011-09-30 15:06:23 -0400347 __this_cpu_add(nmi_stats.normal, handled);
Don Zickusb227e232011-09-30 15:06:22 -0400348 if (handled) {
349 /*
350 * There are cases when a NMI handler handles multiple
351 * events in the current NMI. One of these events may
352 * be queued for in the next NMI. Because the event is
353 * already handled, the next NMI will result in an unknown
354 * NMI. Instead lets flag this for a potential NMI to
355 * swallow.
356 */
357 if (handled > 1)
358 __this_cpu_write(swallow_nmi, true);
Don Zickus1d489222011-09-30 15:06:19 -0400359 return;
Don Zickusb227e232011-09-30 15:06:22 -0400360 }
Don Zickus1d489222011-09-30 15:06:19 -0400361
Hidehiro Kawaib279d672015-12-14 11:19:13 +0100362 /*
363 * Non-CPU-specific NMI: NMI sources can be processed on any CPU.
364 *
365 * Another CPU may be processing panic routines while holding
366 * nmi_reason_lock. Check if the CPU issued the IPI for crash dumping,
367 * and if so, call its callback directly. If there is no CPU preparing
368 * crash dump, we simply loop here.
369 */
370 while (!raw_spin_trylock(&nmi_reason_lock)) {
371 run_crash_ipi_callback(regs);
372 cpu_relax();
373 }
374
Jacob Pan064a59b2011-11-10 13:43:05 +0000375 reason = x86_platform.get_nmi_reason();
Don Zickus1d489222011-09-30 15:06:19 -0400376
377 if (reason & NMI_REASON_MASK) {
378 if (reason & NMI_REASON_SERR)
379 pci_serr_error(reason, regs);
380 else if (reason & NMI_REASON_IOCHK)
381 io_check_error(reason, regs);
382#ifdef CONFIG_X86_32
383 /*
384 * Reassert NMI in case it became active
385 * meanwhile as it's edge-triggered:
386 */
387 reassert_nmi();
388#endif
Don Zickusefc3aac2011-09-30 15:06:23 -0400389 __this_cpu_add(nmi_stats.external, 1);
Don Zickus1d489222011-09-30 15:06:19 -0400390 raw_spin_unlock(&nmi_reason_lock);
391 return;
392 }
393 raw_spin_unlock(&nmi_reason_lock);
394
Don Zickusb227e232011-09-30 15:06:22 -0400395 /*
396 * Only one NMI can be latched at a time. To handle
397 * this we may process multiple nmi handlers at once to
398 * cover the case where an NMI is dropped. The downside
399 * to this approach is we may process an NMI prematurely,
400 * while its real NMI is sitting latched. This will cause
401 * an unknown NMI on the next run of the NMI processing.
402 *
403 * We tried to flag that condition above, by setting the
404 * swallow_nmi flag when we process more than one event.
405 * This condition is also only present on the second half
406 * of a back-to-back NMI, so we flag that condition too.
407 *
408 * If both are true, we assume we already processed this
409 * NMI previously and we swallow it. Otherwise we reset
410 * the logic.
411 *
412 * There are scenarios where we may accidentally swallow
413 * a 'real' unknown NMI. For example, while processing
414 * a perf NMI another perf NMI comes in along with a
415 * 'real' unknown NMI. These two NMIs get combined into
416 * one (as descibed above). When the next NMI gets
417 * processed, it will be flagged by perf as handled, but
418 * noone will know that there was a 'real' unknown NMI sent
419 * also. As a result it gets swallowed. Or if the first
420 * perf NMI returns two events handled then the second
421 * NMI will get eaten by the logic below, again losing a
422 * 'real' unknown NMI. But this is the best we can do
423 * for now.
424 */
425 if (b2b && __this_cpu_read(swallow_nmi))
Don Zickusefc3aac2011-09-30 15:06:23 -0400426 __this_cpu_add(nmi_stats.swallow, 1);
Don Zickusb227e232011-09-30 15:06:22 -0400427 else
428 unknown_nmi_error(reason, regs);
Don Zickus1d489222011-09-30 15:06:19 -0400429}
Masami Hiramatsu93266382014-04-17 17:18:14 +0900430NOKPROBE_SYMBOL(default_do_nmi);
Don Zickus1d489222011-09-30 15:06:19 -0400431
Steven Rostedtccd49c22011-12-13 16:44:16 -0500432/*
Andy Lutomirski0b229302015-07-15 10:29:36 -0700433 * NMIs can page fault or hit breakpoints which will cause it to lose
434 * its NMI context with the CPU when the breakpoint or page fault does an IRET.
Andy Lutomirski9d050412015-07-15 10:29:33 -0700435 *
436 * As a result, NMIs can nest if NMIs get unmasked due an IRET during
437 * NMI processing. On x86_64, the asm glue protects us from nested NMIs
438 * if the outer NMI came from kernel mode, but we can still nest if the
439 * outer NMI came from user mode.
440 *
441 * To handle these nested NMIs, we have three states:
Steven Rostedtccd49c22011-12-13 16:44:16 -0500442 *
443 * 1) not running
444 * 2) executing
445 * 3) latched
446 *
447 * When no NMI is in progress, it is in the "not running" state.
448 * When an NMI comes in, it goes into the "executing" state.
449 * Normally, if another NMI is triggered, it does not interrupt
450 * the running NMI and the HW will simply latch it so that when
451 * the first NMI finishes, it will restart the second NMI.
452 * (Note, the latch is binary, thus multiple NMIs triggering,
453 * when one is running, are ignored. Only one NMI is restarted.)
454 *
Andy Lutomirski9d050412015-07-15 10:29:33 -0700455 * If an NMI executes an iret, another NMI can preempt it. We do not
456 * want to allow this new NMI to run, but we want to execute it when the
457 * first one finishes. We set the state to "latched", and the exit of
458 * the first NMI will perform a dec_return, if the result is zero
459 * (NOT_RUNNING), then it will simply exit the NMI handler. If not, the
460 * dec_return would have set the state to NMI_EXECUTING (what we want it
461 * to be when we are running). In this case, we simply jump back to
462 * rerun the NMI handler again, and restart the 'latched' NMI.
Steven Rostedtc7d65a72012-06-07 11:03:00 -0400463 *
464 * No trap (breakpoint or page fault) should be hit before nmi_restart,
465 * thus there is no race between the first check of state for NOT_RUNNING
466 * and setting it to NMI_EXECUTING. The HW will prevent nested NMIs
467 * at this point.
Steven Rostedt70fb74a2012-06-07 11:54:37 -0400468 *
469 * In case the NMI takes a page fault, we need to save off the CR2
470 * because the NMI could have preempted another page fault and corrupt
471 * the CR2 that is about to be read. As nested NMIs must be restarted
472 * and they can not take breakpoints or page faults, the update of the
473 * CR2 must be done before converting the nmi state back to NOT_RUNNING.
474 * Otherwise, there would be a race of another nested NMI coming in
475 * after setting state to NOT_RUNNING but before updating the nmi_cr2.
Steven Rostedtccd49c22011-12-13 16:44:16 -0500476 */
477enum nmi_states {
Steven Rostedtc7d65a72012-06-07 11:03:00 -0400478 NMI_NOT_RUNNING = 0,
Steven Rostedtccd49c22011-12-13 16:44:16 -0500479 NMI_EXECUTING,
480 NMI_LATCHED,
481};
482static DEFINE_PER_CPU(enum nmi_states, nmi_state);
Steven Rostedt70fb74a2012-06-07 11:54:37 -0400483static DEFINE_PER_CPU(unsigned long, nmi_cr2);
Steven Rostedt228bdaa2011-12-09 03:02:19 -0500484
Andy Lutomirski9d050412015-07-15 10:29:33 -0700485#ifdef CONFIG_X86_64
Steven Rostedtccd49c22011-12-13 16:44:16 -0500486/*
Andy Lutomirski9d050412015-07-15 10:29:33 -0700487 * In x86_64, we need to handle breakpoint -> NMI -> breakpoint. Without
488 * some care, the inner breakpoint will clobber the outer breakpoint's
489 * stack.
Steven Rostedtccd49c22011-12-13 16:44:16 -0500490 *
Andy Lutomirski9d050412015-07-15 10:29:33 -0700491 * If a breakpoint is being processed, and the debug stack is being
492 * used, if an NMI comes in and also hits a breakpoint, the stack
493 * pointer will be set to the same fixed address as the breakpoint that
494 * was interrupted, causing that stack to be corrupted. To handle this
495 * case, check if the stack that was interrupted is the debug stack, and
496 * if so, change the IDT so that new breakpoints will use the current
497 * stack and not switch to the fixed address. On return of the NMI,
498 * switch back to the original IDT.
Steven Rostedtccd49c22011-12-13 16:44:16 -0500499 */
500static DEFINE_PER_CPU(int, update_debug_stack);
Andy Lutomirski9d050412015-07-15 10:29:33 -0700501#endif
Steven Rostedtccd49c22011-12-13 16:44:16 -0500502
Andy Lutomirski9d050412015-07-15 10:29:33 -0700503dotraplinkage notrace void
504do_nmi(struct pt_regs *regs, long error_code)
Steven Rostedtccd49c22011-12-13 16:44:16 -0500505{
Andy Lutomirski9d050412015-07-15 10:29:33 -0700506 if (this_cpu_read(nmi_state) != NMI_NOT_RUNNING) {
507 this_cpu_write(nmi_state, NMI_LATCHED);
508 return;
509 }
510 this_cpu_write(nmi_state, NMI_EXECUTING);
511 this_cpu_write(nmi_cr2, read_cr2());
512nmi_restart:
513
514#ifdef CONFIG_X86_64
Steven Rostedt228bdaa2011-12-09 03:02:19 -0500515 /*
516 * If we interrupted a breakpoint, it is possible that
517 * the nmi handler will have breakpoints too. We need to
518 * change the IDT such that breakpoints that happen here
519 * continue to use the NMI stack.
520 */
521 if (unlikely(is_debug_stack(regs->sp))) {
522 debug_stack_set_zero();
Steven Rostedtc0525a62012-05-30 11:43:19 -0400523 this_cpu_write(update_debug_stack, 1);
Steven Rostedt228bdaa2011-12-09 03:02:19 -0500524 }
Steven Rostedtccd49c22011-12-13 16:44:16 -0500525#endif
526
Don Zickus1d489222011-09-30 15:06:19 -0400527 nmi_enter();
528
529 inc_irq_stat(__nmi_count);
530
531 if (!ignore_nmis)
532 default_do_nmi(regs);
533
534 nmi_exit();
Steven Rostedt228bdaa2011-12-09 03:02:19 -0500535
Andy Lutomirski9d050412015-07-15 10:29:33 -0700536#ifdef CONFIG_X86_64
537 if (unlikely(this_cpu_read(update_debug_stack))) {
538 debug_stack_reset();
539 this_cpu_write(update_debug_stack, 0);
540 }
541#endif
542
543 if (unlikely(this_cpu_read(nmi_cr2) != read_cr2()))
544 write_cr2(this_cpu_read(nmi_cr2));
545 if (this_cpu_dec_return(nmi_state))
546 goto nmi_restart;
Don Zickus1d489222011-09-30 15:06:19 -0400547}
Masami Hiramatsu93266382014-04-17 17:18:14 +0900548NOKPROBE_SYMBOL(do_nmi);
Don Zickus1d489222011-09-30 15:06:19 -0400549
550void stop_nmi(void)
551{
552 ignore_nmis++;
553}
554
555void restart_nmi(void)
556{
557 ignore_nmis--;
558}
Don Zickusb227e232011-09-30 15:06:22 -0400559
560/* reset the back-to-back NMI logic */
561void local_touch_nmi(void)
562{
563 __this_cpu_write(last_nmi_rip, 0);
564}
Jacob Pan29c6fb72013-01-04 11:12:44 +0000565EXPORT_SYMBOL_GPL(local_touch_nmi);