xref: /openbmc/linux/drivers/ras/cec.c (revision d25c6948)
1 // SPDX-License-Identifier: GPL-2.0
2 /*
3  * Copyright (c) 2017-2019 Borislav Petkov, SUSE Labs.
4  */
5 #include <linux/mm.h>
6 #include <linux/gfp.h>
7 #include <linux/ras.h>
8 #include <linux/kernel.h>
9 #include <linux/workqueue.h>
10 
11 #include <asm/mce.h>
12 
13 #include "debugfs.h"
14 
15 /*
16  * RAS Correctable Errors Collector
17  *
18  * This is a simple gadget which collects correctable errors and counts their
19  * occurrence per physical page address.
20  *
21  * We've opted for possibly the simplest data structure to collect those - an
22  * array of the size of a memory page. It stores 512 u64's with the following
23  * structure:
24  *
25  * [63 ... PFN ... 12 | 11 ... generation ... 10 | 9 ... count ... 0]
26  *
27  * The generation in the two highest order bits is two bits which are set to 11b
28  * on every insertion. During the course of each entry's existence, the
29  * generation field gets decremented during spring cleaning to 10b, then 01b and
30  * then 00b.
31  *
32  * This way we're employing the natural numeric ordering to make sure that newly
33  * inserted/touched elements have higher 12-bit counts (which we've manufactured)
34  * and thus iterating over the array initially won't kick out those elements
35  * which were inserted last.
36  *
37  * Spring cleaning is what we do when we reach a certain number CLEAN_ELEMS of
38  * elements entered into the array, during which, we're decaying all elements.
39  * If, after decay, an element gets inserted again, its generation is set to 11b
40  * to make sure it has higher numerical count than other, older elements and
41  * thus emulate an LRU-like behavior when deleting elements to free up space
42  * in the page.
43  *
44  * When an element reaches it's max count of action_threshold, we try to poison
45  * it by assuming that errors triggered action_threshold times in a single page
46  * are excessive and that page shouldn't be used anymore. action_threshold is
47  * initialized to COUNT_MASK which is the maximum.
48  *
49  * That error event entry causes cec_add_elem() to return !0 value and thus
50  * signal to its callers to log the error.
51  *
52  * To the question why we've chosen a page and moving elements around with
53  * memmove(), it is because it is a very simple structure to handle and max data
54  * movement is 4K which on highly optimized modern CPUs is almost unnoticeable.
55  * We wanted to avoid the pointer traversal of more complex structures like a
56  * linked list or some sort of a balancing search tree.
57  *
58  * Deleting an element takes O(n) but since it is only a single page, it should
59  * be fast enough and it shouldn't happen all too often depending on error
60  * patterns.
61  */
62 
63 #undef pr_fmt
64 #define pr_fmt(fmt) "RAS: " fmt
65 
66 /*
67  * We use DECAY_BITS bits of PAGE_SHIFT bits for counting decay, i.e., how long
68  * elements have stayed in the array without having been accessed again.
69  */
70 #define DECAY_BITS		2
71 #define DECAY_MASK		((1ULL << DECAY_BITS) - 1)
72 #define MAX_ELEMS		(PAGE_SIZE / sizeof(u64))
73 
74 /*
75  * Threshold amount of inserted elements after which we start spring
76  * cleaning.
77  */
78 #define CLEAN_ELEMS		(MAX_ELEMS >> DECAY_BITS)
79 
80 /* Bits which count the number of errors happened in this 4K page. */
81 #define COUNT_BITS		(PAGE_SHIFT - DECAY_BITS)
82 #define COUNT_MASK		((1ULL << COUNT_BITS) - 1)
83 #define FULL_COUNT_MASK		(PAGE_SIZE - 1)
84 
85 /*
86  * u64: [ 63 ... 12 | DECAY_BITS | COUNT_BITS ]
87  */
88 
89 #define PFN(e)			((e) >> PAGE_SHIFT)
90 #define DECAY(e)		(((e) >> COUNT_BITS) & DECAY_MASK)
91 #define COUNT(e)		((unsigned int)(e) & COUNT_MASK)
92 #define FULL_COUNT(e)		((e) & (PAGE_SIZE - 1))
93 
94 static struct ce_array {
95 	u64 *array;			/* container page */
96 	unsigned int n;			/* number of elements in the array */
97 
98 	unsigned int decay_count;	/*
99 					 * number of element insertions/increments
100 					 * since the last spring cleaning.
101 					 */
102 
103 	u64 pfns_poisoned;		/*
104 					 * number of PFNs which got poisoned.
105 					 */
106 
107 	u64 ces_entered;		/*
108 					 * The number of correctable errors
109 					 * entered into the collector.
110 					 */
111 
112 	u64 decays_done;		/*
113 					 * Times we did spring cleaning.
114 					 */
115 
116 	union {
117 		struct {
118 			__u32	disabled : 1,	/* cmdline disabled */
119 			__resv   : 31;
120 		};
121 		__u32 flags;
122 	};
123 } ce_arr;
124 
125 static DEFINE_MUTEX(ce_mutex);
126 static u64 dfs_pfn;
127 
128 /* Amount of errors after which we offline */
129 static u64 action_threshold = COUNT_MASK;
130 
131 /* Each element "decays" each decay_interval which is 24hrs by default. */
132 #define CEC_DECAY_DEFAULT_INTERVAL	24 * 60 * 60	/* 24 hrs */
133 #define CEC_DECAY_MIN_INTERVAL		 1 * 60 * 60	/* 1h */
134 #define CEC_DECAY_MAX_INTERVAL	   30 *	24 * 60 * 60	/* one month */
135 static struct delayed_work cec_work;
136 static u64 decay_interval = CEC_DECAY_DEFAULT_INTERVAL;
137 
138 /*
139  * Decrement decay value. We're using DECAY_BITS bits to denote decay of an
140  * element in the array. On insertion and any access, it gets reset to max.
141  */
do_spring_cleaning(struct ce_array * ca)142 static void do_spring_cleaning(struct ce_array *ca)
143 {
144 	int i;
145 
146 	for (i = 0; i < ca->n; i++) {
147 		u8 decay = DECAY(ca->array[i]);
148 
149 		if (!decay)
150 			continue;
151 
152 		decay--;
153 
154 		ca->array[i] &= ~(DECAY_MASK << COUNT_BITS);
155 		ca->array[i] |= (decay << COUNT_BITS);
156 	}
157 	ca->decay_count = 0;
158 	ca->decays_done++;
159 }
160 
161 /*
162  * @interval in seconds
163  */
cec_mod_work(unsigned long interval)164 static void cec_mod_work(unsigned long interval)
165 {
166 	unsigned long iv;
167 
168 	iv = interval * HZ;
169 	mod_delayed_work(system_wq, &cec_work, round_jiffies(iv));
170 }
171 
cec_work_fn(struct work_struct * work)172 static void cec_work_fn(struct work_struct *work)
173 {
174 	mutex_lock(&ce_mutex);
175 	do_spring_cleaning(&ce_arr);
176 	mutex_unlock(&ce_mutex);
177 
178 	cec_mod_work(decay_interval);
179 }
180 
181 /*
182  * @to: index of the smallest element which is >= then @pfn.
183  *
184  * Return the index of the pfn if found, otherwise negative value.
185  */
__find_elem(struct ce_array * ca,u64 pfn,unsigned int * to)186 static int __find_elem(struct ce_array *ca, u64 pfn, unsigned int *to)
187 {
188 	int min = 0, max = ca->n - 1;
189 	u64 this_pfn;
190 
191 	while (min <= max) {
192 		int i = (min + max) >> 1;
193 
194 		this_pfn = PFN(ca->array[i]);
195 
196 		if (this_pfn < pfn)
197 			min = i + 1;
198 		else if (this_pfn > pfn)
199 			max = i - 1;
200 		else if (this_pfn == pfn) {
201 			if (to)
202 				*to = i;
203 
204 			return i;
205 		}
206 	}
207 
208 	/*
209 	 * When the loop terminates without finding @pfn, min has the index of
210 	 * the element slot where the new @pfn should be inserted. The loop
211 	 * terminates when min > max, which means the min index points to the
212 	 * bigger element while the max index to the smaller element, in-between
213 	 * which the new @pfn belongs to.
214 	 *
215 	 * For more details, see exercise 1, Section 6.2.1 in TAOCP, vol. 3.
216 	 */
217 	if (to)
218 		*to = min;
219 
220 	return -ENOKEY;
221 }
222 
find_elem(struct ce_array * ca,u64 pfn,unsigned int * to)223 static int find_elem(struct ce_array *ca, u64 pfn, unsigned int *to)
224 {
225 	WARN_ON(!to);
226 
227 	if (!ca->n) {
228 		*to = 0;
229 		return -ENOKEY;
230 	}
231 	return __find_elem(ca, pfn, to);
232 }
233 
del_elem(struct ce_array * ca,int idx)234 static void del_elem(struct ce_array *ca, int idx)
235 {
236 	/* Save us a function call when deleting the last element. */
237 	if (ca->n - (idx + 1))
238 		memmove((void *)&ca->array[idx],
239 			(void *)&ca->array[idx + 1],
240 			(ca->n - (idx + 1)) * sizeof(u64));
241 
242 	ca->n--;
243 }
244 
del_lru_elem_unlocked(struct ce_array * ca)245 static u64 del_lru_elem_unlocked(struct ce_array *ca)
246 {
247 	unsigned int min = FULL_COUNT_MASK;
248 	int i, min_idx = 0;
249 
250 	for (i = 0; i < ca->n; i++) {
251 		unsigned int this = FULL_COUNT(ca->array[i]);
252 
253 		if (min > this) {
254 			min = this;
255 			min_idx = i;
256 		}
257 	}
258 
259 	del_elem(ca, min_idx);
260 
261 	return PFN(ca->array[min_idx]);
262 }
263 
264 /*
265  * We return the 0th pfn in the error case under the assumption that it cannot
266  * be poisoned and excessive CEs in there are a serious deal anyway.
267  */
del_lru_elem(void)268 static u64 __maybe_unused del_lru_elem(void)
269 {
270 	struct ce_array *ca = &ce_arr;
271 	u64 pfn;
272 
273 	if (!ca->n)
274 		return 0;
275 
276 	mutex_lock(&ce_mutex);
277 	pfn = del_lru_elem_unlocked(ca);
278 	mutex_unlock(&ce_mutex);
279 
280 	return pfn;
281 }
282 
sanity_check(struct ce_array * ca)283 static bool sanity_check(struct ce_array *ca)
284 {
285 	bool ret = false;
286 	u64 prev = 0;
287 	int i;
288 
289 	for (i = 0; i < ca->n; i++) {
290 		u64 this = PFN(ca->array[i]);
291 
292 		if (WARN(prev > this, "prev: 0x%016llx <-> this: 0x%016llx\n", prev, this))
293 			ret = true;
294 
295 		prev = this;
296 	}
297 
298 	if (!ret)
299 		return ret;
300 
301 	pr_info("Sanity check dump:\n{ n: %d\n", ca->n);
302 	for (i = 0; i < ca->n; i++) {
303 		u64 this = PFN(ca->array[i]);
304 
305 		pr_info(" %03d: [%016llx|%03llx]\n", i, this, FULL_COUNT(ca->array[i]));
306 	}
307 	pr_info("}\n");
308 
309 	return ret;
310 }
311 
312 /**
313  * cec_add_elem - Add an element to the CEC array.
314  * @pfn:	page frame number to insert
315  *
316  * Return values:
317  * - <0:	on error
318  * -  0:	on success
319  * - >0:	when the inserted pfn was offlined
320  */
cec_add_elem(u64 pfn)321 static int cec_add_elem(u64 pfn)
322 {
323 	struct ce_array *ca = &ce_arr;
324 	int count, err, ret = 0;
325 	unsigned int to = 0;
326 
327 	/*
328 	 * We can be called very early on the identify_cpu() path where we are
329 	 * not initialized yet. We ignore the error for simplicity.
330 	 */
331 	if (!ce_arr.array || ce_arr.disabled)
332 		return -ENODEV;
333 
334 	mutex_lock(&ce_mutex);
335 
336 	ca->ces_entered++;
337 
338 	/* Array full, free the LRU slot. */
339 	if (ca->n == MAX_ELEMS)
340 		WARN_ON(!del_lru_elem_unlocked(ca));
341 
342 	err = find_elem(ca, pfn, &to);
343 	if (err < 0) {
344 		/*
345 		 * Shift range [to-end] to make room for one more element.
346 		 */
347 		memmove((void *)&ca->array[to + 1],
348 			(void *)&ca->array[to],
349 			(ca->n - to) * sizeof(u64));
350 
351 		ca->array[to] = pfn << PAGE_SHIFT;
352 		ca->n++;
353 	}
354 
355 	/* Add/refresh element generation and increment count */
356 	ca->array[to] |= DECAY_MASK << COUNT_BITS;
357 	ca->array[to]++;
358 
359 	/* Check action threshold and soft-offline, if reached. */
360 	count = COUNT(ca->array[to]);
361 	if (count >= action_threshold) {
362 		u64 pfn = ca->array[to] >> PAGE_SHIFT;
363 
364 		if (!pfn_valid(pfn)) {
365 			pr_warn("CEC: Invalid pfn: 0x%llx\n", pfn);
366 		} else {
367 			/* We have reached max count for this page, soft-offline it. */
368 			pr_err("Soft-offlining pfn: 0x%llx\n", pfn);
369 			memory_failure_queue(pfn, MF_SOFT_OFFLINE);
370 			ca->pfns_poisoned++;
371 		}
372 
373 		del_elem(ca, to);
374 
375 		/*
376 		 * Return a >0 value to callers, to denote that we've reached
377 		 * the offlining threshold.
378 		 */
379 		ret = 1;
380 
381 		goto unlock;
382 	}
383 
384 	ca->decay_count++;
385 
386 	if (ca->decay_count >= CLEAN_ELEMS)
387 		do_spring_cleaning(ca);
388 
389 	WARN_ON_ONCE(sanity_check(ca));
390 
391 unlock:
392 	mutex_unlock(&ce_mutex);
393 
394 	return ret;
395 }
396 
u64_get(void * data,u64 * val)397 static int u64_get(void *data, u64 *val)
398 {
399 	*val = *(u64 *)data;
400 
401 	return 0;
402 }
403 
pfn_set(void * data,u64 val)404 static int pfn_set(void *data, u64 val)
405 {
406 	*(u64 *)data = val;
407 
408 	cec_add_elem(val);
409 
410 	return 0;
411 }
412 
413 DEFINE_DEBUGFS_ATTRIBUTE(pfn_ops, u64_get, pfn_set, "0x%llx\n");
414 
decay_interval_set(void * data,u64 val)415 static int decay_interval_set(void *data, u64 val)
416 {
417 	if (val < CEC_DECAY_MIN_INTERVAL)
418 		return -EINVAL;
419 
420 	if (val > CEC_DECAY_MAX_INTERVAL)
421 		return -EINVAL;
422 
423 	*(u64 *)data   = val;
424 	decay_interval = val;
425 
426 	cec_mod_work(decay_interval);
427 
428 	return 0;
429 }
430 DEFINE_DEBUGFS_ATTRIBUTE(decay_interval_ops, u64_get, decay_interval_set, "%lld\n");
431 
action_threshold_set(void * data,u64 val)432 static int action_threshold_set(void *data, u64 val)
433 {
434 	*(u64 *)data = val;
435 
436 	if (val > COUNT_MASK)
437 		val = COUNT_MASK;
438 
439 	action_threshold = val;
440 
441 	return 0;
442 }
443 DEFINE_DEBUGFS_ATTRIBUTE(action_threshold_ops, u64_get, action_threshold_set, "%lld\n");
444 
445 static const char * const bins[] = { "00", "01", "10", "11" };
446 
array_show(struct seq_file * m,void * v)447 static int array_show(struct seq_file *m, void *v)
448 {
449 	struct ce_array *ca = &ce_arr;
450 	int i;
451 
452 	mutex_lock(&ce_mutex);
453 
454 	seq_printf(m, "{ n: %d\n", ca->n);
455 	for (i = 0; i < ca->n; i++) {
456 		u64 this = PFN(ca->array[i]);
457 
458 		seq_printf(m, " %3d: [%016llx|%s|%03llx]\n",
459 			   i, this, bins[DECAY(ca->array[i])], COUNT(ca->array[i]));
460 	}
461 
462 	seq_printf(m, "}\n");
463 
464 	seq_printf(m, "Stats:\nCEs: %llu\nofflined pages: %llu\n",
465 		   ca->ces_entered, ca->pfns_poisoned);
466 
467 	seq_printf(m, "Flags: 0x%x\n", ca->flags);
468 
469 	seq_printf(m, "Decay interval: %lld seconds\n", decay_interval);
470 	seq_printf(m, "Decays: %lld\n", ca->decays_done);
471 
472 	seq_printf(m, "Action threshold: %lld\n", action_threshold);
473 
474 	mutex_unlock(&ce_mutex);
475 
476 	return 0;
477 }
478 
479 DEFINE_SHOW_ATTRIBUTE(array);
480 
create_debugfs_nodes(void)481 static int __init create_debugfs_nodes(void)
482 {
483 	struct dentry *d, *pfn, *decay, *count, *array;
484 
485 	d = debugfs_create_dir("cec", ras_debugfs_dir);
486 	if (!d) {
487 		pr_warn("Error creating cec debugfs node!\n");
488 		return -1;
489 	}
490 
491 	decay = debugfs_create_file("decay_interval", S_IRUSR | S_IWUSR, d,
492 				    &decay_interval, &decay_interval_ops);
493 	if (!decay) {
494 		pr_warn("Error creating decay_interval debugfs node!\n");
495 		goto err;
496 	}
497 
498 	count = debugfs_create_file("action_threshold", S_IRUSR | S_IWUSR, d,
499 				    &action_threshold, &action_threshold_ops);
500 	if (!count) {
501 		pr_warn("Error creating action_threshold debugfs node!\n");
502 		goto err;
503 	}
504 
505 	if (!IS_ENABLED(CONFIG_RAS_CEC_DEBUG))
506 		return 0;
507 
508 	pfn = debugfs_create_file("pfn", S_IRUSR | S_IWUSR, d, &dfs_pfn, &pfn_ops);
509 	if (!pfn) {
510 		pr_warn("Error creating pfn debugfs node!\n");
511 		goto err;
512 	}
513 
514 	array = debugfs_create_file("array", S_IRUSR, d, NULL, &array_fops);
515 	if (!array) {
516 		pr_warn("Error creating array debugfs node!\n");
517 		goto err;
518 	}
519 
520 	return 0;
521 
522 err:
523 	debugfs_remove_recursive(d);
524 
525 	return 1;
526 }
527 
cec_notifier(struct notifier_block * nb,unsigned long val,void * data)528 static int cec_notifier(struct notifier_block *nb, unsigned long val,
529 			void *data)
530 {
531 	struct mce *m = (struct mce *)data;
532 
533 	if (!m)
534 		return NOTIFY_DONE;
535 
536 	/* We eat only correctable DRAM errors with usable addresses. */
537 	if (mce_is_memory_error(m) &&
538 	    mce_is_correctable(m)  &&
539 	    mce_usable_address(m)) {
540 		if (!cec_add_elem(m->addr >> PAGE_SHIFT)) {
541 			m->kflags |= MCE_HANDLED_CEC;
542 			return NOTIFY_OK;
543 		}
544 	}
545 
546 	return NOTIFY_DONE;
547 }
548 
549 static struct notifier_block cec_nb = {
550 	.notifier_call	= cec_notifier,
551 	.priority	= MCE_PRIO_CEC,
552 };
553 
cec_init(void)554 static int __init cec_init(void)
555 {
556 	if (ce_arr.disabled)
557 		return -ENODEV;
558 
559 	/*
560 	 * Intel systems may avoid uncorrectable errors
561 	 * if pages with corrected errors are aggressively
562 	 * taken offline.
563 	 */
564 	if (boot_cpu_data.x86_vendor == X86_VENDOR_INTEL)
565 		action_threshold = 2;
566 
567 	ce_arr.array = (void *)get_zeroed_page(GFP_KERNEL);
568 	if (!ce_arr.array) {
569 		pr_err("Error allocating CE array page!\n");
570 		return -ENOMEM;
571 	}
572 
573 	if (create_debugfs_nodes()) {
574 		free_page((unsigned long)ce_arr.array);
575 		return -ENOMEM;
576 	}
577 
578 	INIT_DELAYED_WORK(&cec_work, cec_work_fn);
579 	schedule_delayed_work(&cec_work, CEC_DECAY_DEFAULT_INTERVAL);
580 
581 	mce_register_decode_chain(&cec_nb);
582 
583 	pr_info("Correctable Errors collector initialized.\n");
584 	return 0;
585 }
586 late_initcall(cec_init);
587 
parse_cec_param(char * str)588 int __init parse_cec_param(char *str)
589 {
590 	if (!str)
591 		return 0;
592 
593 	if (*str == '=')
594 		str++;
595 
596 	if (!strcmp(str, "cec_disable"))
597 		ce_arr.disabled = 1;
598 	else
599 		return 0;
600 
601 	return 1;
602 }
603