summaryrefslogtreecommitdiffstats
path: root/drivers/ras/cec.c
blob: c09cf55e2d2040031b0688d827d806f57db9df13 (plain)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346
347
348
349
350
351
352
353
354
355
356
357
358
359
360
361
362
363
364
365
366
367
368
369
370
371
372
373
374
375
376
377
378
379
380
381
382
383
384
385
386
387
388
389
390
391
392
393
394
395
396
397
398
399
400
401
402
403
404
405
406
407
408
409
410
411
412
413
414
415
416
417
418
419
420
421
422
423
424
425
426
427
428
429
430
431
432
433
434
435
436
437
438
439
440
441
442
443
444
445
446
447
448
449
450
451
452
453
454
455
456
457
458
459
460
461
462
463
464
465
466
467
468
469
470
471
472
473
474
475
476
477
478
479
480
481
482
483
484
485
486
487
488
489
490
491
492
493
494
495
496
497
498
499
500
501
502
503
504
505
506
507
508
509
510
511
512
513
514
515
516
517
518
519
520
521
522
523
524
525
526
527
528
529
530
531
532
533
534
535
536
537
538
539
540
541
542
543
544
545
546
547
548
549
550
551
552
553
554
555
556
557
558
559
560
561
562
563
564
565
566
// SPDX-License-Identifier: GPL-2.0
/*
 * Copyright (c) 2017-2019 Borislav Petkov, SUSE Labs.
 */
#include <linux/mm.h>
#include <linux/gfp.h>
#include <linux/ras.h>
#include <linux/kernel.h>
#include <linux/workqueue.h>

#include <asm/mce.h>

#include "debugfs.h"

/*
 * RAS Correctable Errors Collector
 *
 * This is a simple gadget which collects correctable errors and counts their
 * occurrence per physical page address.
 *
 * We've opted for possibly the simplest data structure to collect those - an
 * array of the size of a memory page. It stores 512 u64's with the following
 * structure:
 *
 * [63 ... PFN ... 12 | 11 ... generation ... 10 | 9 ... count ... 0]
 *
 * The generation in the two highest order bits is two bits which are set to 11b
 * on every insertion. During the course of each entry's existence, the
 * generation field gets decremented during spring cleaning to 10b, then 01b and
 * then 00b.
 *
 * This way we're employing the natural numeric ordering to make sure that newly
 * inserted/touched elements have higher 12-bit counts (which we've manufactured)
 * and thus iterating over the array initially won't kick out those elements
 * which were inserted last.
 *
 * Spring cleaning is what we do when we reach a certain number CLEAN_ELEMS of
 * elements entered into the array, during which, we're decaying all elements.
 * If, after decay, an element gets inserted again, its generation is set to 11b
 * to make sure it has higher numerical count than other, older elements and
 * thus emulate an an LRU-like behavior when deleting elements to free up space
 * in the page.
 *
 * When an element reaches it's max count of action_threshold, we try to poison
 * it by assuming that errors triggered action_threshold times in a single page
 * are excessive and that page shouldn't be used anymore. action_threshold is
 * initialized to COUNT_MASK which is the maximum.
 *
 * That error event entry causes cec_add_elem() to return !0 value and thus
 * signal to its callers to log the error.
 *
 * To the question why we've chosen a page and moving elements around with
 * memmove(), it is because it is a very simple structure to handle and max data
 * movement is 4K which on highly optimized modern CPUs is almost unnoticeable.
 * We wanted to avoid the pointer traversal of more complex structures like a
 * linked list or some sort of a balancing search tree.
 *
 * Deleting an element takes O(n) but since it is only a single page, it should
 * be fast enough and it shouldn't happen all too often depending on error
 * patterns.
 */

#undef pr_fmt
#define pr_fmt(fmt) "RAS: " fmt

/*
 * We use DECAY_BITS bits of PAGE_SHIFT bits for counting decay, i.e., how long
 * elements have stayed in the array without having been accessed again.
 */
#define DECAY_BITS		2
#define DECAY_MASK		((1ULL << DECAY_BITS) - 1)
#define MAX_ELEMS		(PAGE_SIZE / sizeof(u64))

/*
 * Threshold amount of inserted elements after which we start spring
 * cleaning.
 */
#define CLEAN_ELEMS		(MAX_ELEMS >> DECAY_BITS)

/* Bits which count the number of errors happened in this 4K page. */
#define COUNT_BITS		(PAGE_SHIFT - DECAY_BITS)
#define COUNT_MASK		((1ULL << COUNT_BITS) - 1)
#define FULL_COUNT_MASK		(PAGE_SIZE - 1)

/*
 * u64: [ 63 ... 12 | DECAY_BITS | COUNT_BITS ]
 */

#define PFN(e)			((e) >> PAGE_SHIFT)
#define DECAY(e)		(((e) >> COUNT_BITS) & DECAY_MASK)
#define COUNT(e)		((unsigned int)(e) & COUNT_MASK)
#define FULL_COUNT(e)		((e) & (PAGE_SIZE - 1))

static struct ce_array {
	u64 *array;			/* container page */
	unsigned int n;			/* number of elements in the array */

	unsigned int decay_count;	/*
					 * number of element insertions/increments
					 * since the last spring cleaning.
					 */

	u64 pfns_poisoned;		/*
					 * number of PFNs which got poisoned.
					 */

	u64 ces_entered;		/*
					 * The number of correctable errors
					 * entered into the collector.
					 */

	u64 decays_done;		/*
					 * Times we did spring cleaning.
					 */

	union {
		struct {
			__u32	disabled : 1,	/* cmdline disabled */
			__resv   : 31;
		};
		__u32 flags;
	};
} ce_arr;

static DEFINE_MUTEX(ce_mutex);
static u64 dfs_pfn;

/* Amount of errors after which we offline */
static u64 action_threshold = COUNT_MASK;

/* Each element "decays" each decay_interval which is 24hrs by default. */
#define CEC_DECAY_DEFAULT_INTERVAL	24 * 60 * 60	/* 24 hrs */
#define CEC_DECAY_MIN_INTERVAL		 1 * 60 * 60	/* 1h */
#define CEC_DECAY_MAX_INTERVAL	   30 *	24 * 60 * 60	/* one month */
static struct delayed_work cec_work;
static u64 decay_interval = CEC_DECAY_DEFAULT_INTERVAL;

/*
 * Decrement decay value. We're using DECAY_BITS bits to denote decay of an
 * element in the array. On insertion and any access, it gets reset to max.
 */
static void do_spring_cleaning(struct ce_array *ca)
{
	int i;

	for (i = 0; i < ca->n; i++) {
		u8 decay = DECAY(ca->array[i]);

		if (!decay)
			continue;

		decay--;

		ca->array[i] &= ~(DECAY_MASK << COUNT_BITS);
		ca->array[i] |= (decay << COUNT_BITS);
	}
	ca->decay_count = 0;
	ca->decays_done++;
}

/*
 * @interval in seconds
 */
static void cec_mod_work(unsigned long interval)
{
	unsigned long iv;

	iv = interval * HZ;
	mod_delayed_work(system_wq, &cec_work, round_jiffies(iv));
}

static void cec_work_fn(struct work_struct *work)
{
	mutex_lock(&ce_mutex);
	do_spring_cleaning(&ce_arr);
	mutex_unlock(&ce_mutex);

	cec_mod_work(decay_interval);
}

/*
 * @to: index of the smallest element which is >= then @pfn.
 *
 * Return the index of the pfn if found, otherwise negative value.
 */
static int __find_elem(struct ce_array *ca, u64 pfn, unsigned int *to)
{
	int min = 0, max = ca->n - 1;
	u64 this_pfn;

	while (min <= max) {
		int i = (min + max) >> 1;

		this_pfn = PFN(ca->array[i]);

		if (this_pfn < pfn)
			min = i + 1;
		else if (this_pfn > pfn)
			max = i - 1;
		else if (this_pfn == pfn) {
			if (to)
				*to = i;

			return i;
		}
	}

	/*
	 * When the loop terminates without finding @pfn, min has the index of
	 * the element slot where the new @pfn should be inserted. The loop
	 * terminates when min > max, which means the min index points to the
	 * bigger element while the max index to the smaller element, in-between
	 * which the new @pfn belongs to.
	 *
	 * For more details, see exercise 1, Section 6.2.1 in TAOCP, vol. 3.
	 */
	if (to)
		*to = min;

	return -ENOKEY;
}

static int find_elem(struct ce_array *ca, u64 pfn, unsigned int *to)
{
	WARN_ON(!to);

	if (!ca->n) {
		*to = 0;
		return -ENOKEY;
	}
	return __find_elem(ca, pfn, to);
}

static void del_elem(struct ce_array *ca, int idx)
{
	/* Save us a function call when deleting the last element. */
	if (ca->n - (idx + 1))
		memmove((void *)&ca->array[idx],
			(void *)&ca->array[idx + 1],
			(ca->n - (idx + 1)) * sizeof(u64));

	ca->n--;
}

static u64 del_lru_elem_unlocked(struct ce_array *ca)
{
	unsigned int min = FULL_COUNT_MASK;
	int i, min_idx = 0;

	for (i = 0; i < ca->n; i++) {
		unsigned int this = FULL_COUNT(ca->array[i]);

		if (min > this) {
			min = this;
			min_idx = i;
		}
	}

	del_elem(ca, min_idx);

	return PFN(ca->array[min_idx]);
}

/*
 * We return the 0th pfn in the error case under the assumption that it cannot
 * be poisoned and excessive CEs in there are a serious deal anyway.
 */
static u64 __maybe_unused del_lru_elem(void)
{
	struct ce_array *ca = &ce_arr;
	u64 pfn;

	if (!ca->n)
		return 0;

	mutex_lock(&ce_mutex);
	pfn = del_lru_elem_unlocked(ca);
	mutex_unlock(&ce_mutex);

	return pfn;
}

static bool sanity_check(struct ce_array *ca)
{
	bool ret = false;
	u64 prev = 0;
	int i;

	for (i = 0; i < ca->n; i++) {
		u64 this = PFN(ca->array[i]);

		if (WARN(prev > this, "prev: 0x%016llx <-> this: 0x%016llx\n", prev, this))
			ret = true;

		prev = this;
	}

	if (!ret)
		return ret;

	pr_info("Sanity check dump:\n{ n: %d\n", ca->n);
	for (i = 0; i < ca->n; i++) {
		u64 this = PFN(ca->array[i]);

		pr_info(" %03d: [%016llx|%03llx]\n", i, this, FULL_COUNT(ca->array[i]));
	}
	pr_info("}\n");

	return ret;
}

int cec_add_elem(u64 pfn)
{
	struct ce_array *ca = &ce_arr;
	unsigned int to = 0;
	int count, ret = 0;

	/*
	 * We can be called very early on the identify_cpu() path where we are
	 * not initialized yet. We ignore the error for simplicity.
	 */
	if (!ce_arr.array || ce_arr.disabled)
		return -ENODEV;

	mutex_lock(&ce_mutex);

	ca->ces_entered++;

	/* Array full, free the LRU slot. */
	if (ca->n == MAX_ELEMS)
		WARN_ON(!del_lru_elem_unlocked(ca));

	ret = find_elem(ca, pfn, &to);
	if (ret < 0) {
		/*
		 * Shift range [to-end] to make room for one more element.
		 */
		memmove((void *)&ca->array[to + 1],
			(void *)&ca->array[to],
			(ca->n - to) * sizeof(u64));

		ca->array[to] = pfn << PAGE_SHIFT;
		ca->n++;
	}

	/* Add/refresh element generation and increment count */
	ca->array[to] |= DECAY_MASK << COUNT_BITS;
	ca->array[to]++;

	/* Check action threshold and soft-offline, if reached. */
	count = COUNT(ca->array[to]);
	if (count >= action_threshold) {
		u64 pfn = ca->array[to] >> PAGE_SHIFT;

		if (!pfn_valid(pfn)) {
			pr_warn("CEC: Invalid pfn: 0x%llx\n", pfn);
		} else {
			/* We have reached max count for this page, soft-offline it. */
			pr_err("Soft-offlining pfn: 0x%llx\n", pfn);
			memory_failure_queue(pfn, MF_SOFT_OFFLINE);
			ca->pfns_poisoned++;
		}

		del_elem(ca, to);

		/*
		 * Return a >0 value to callers, to denote that we've reached
		 * the offlining threshold.
		 */
		ret = 1;

		goto unlock;
	}

	ca->decay_count++;

	if (ca->decay_count >= CLEAN_ELEMS)
		do_spring_cleaning(ca);

	WARN_ON_ONCE(sanity_check(ca));

unlock:
	mutex_unlock(&ce_mutex);

	return ret;
}

static int u64_get(void *data, u64 *val)
{
	*val = *(u64 *)data;

	return 0;
}

static int pfn_set(void *data, u64 val)
{
	*(u64 *)data = val;

	cec_add_elem(val);

	return 0;
}

DEFINE_DEBUGFS_ATTRIBUTE(pfn_ops, u64_get, pfn_set, "0x%llx\n");

static int decay_interval_set(void *data, u64 val)
{
	if (val < CEC_DECAY_MIN_INTERVAL)
		return -EINVAL;

	if (val > CEC_DECAY_MAX_INTERVAL)
		return -EINVAL;

	*(u64 *)data   = val;
	decay_interval = val;

	cec_mod_work(decay_interval);

	return 0;
}
DEFINE_DEBUGFS_ATTRIBUTE(decay_interval_ops, u64_get, decay_interval_set, "%lld\n");

static int action_threshold_set(void *data, u64 val)
{
	*(u64 *)data = val;

	if (val > COUNT_MASK)
		val = COUNT_MASK;

	action_threshold = val;

	return 0;
}
DEFINE_DEBUGFS_ATTRIBUTE(action_threshold_ops, u64_get, action_threshold_set, "%lld\n");

static const char * const bins[] = { "00", "01", "10", "11" };

static int array_dump(struct seq_file *m, void *v)
{
	struct ce_array *ca = &ce_arr;
	int i;

	mutex_lock(&ce_mutex);

	seq_printf(m, "{ n: %d\n", ca->n);
	for (i = 0; i < ca->n; i++) {
		u64 this = PFN(ca->array[i]);

		seq_printf(m, " %3d: [%016llx|%s|%03llx]\n",
			   i, this, bins[DECAY(ca->array[i])], COUNT(ca->array[i]));
	}

	seq_printf(m, "}\n");

	seq_printf(m, "Stats:\nCEs: %llu\nofflined pages: %llu\n",
		   ca->ces_entered, ca->pfns_poisoned);

	seq_printf(m, "Flags: 0x%x\n", ca->flags);

	seq_printf(m, "Decay interval: %lld seconds\n", decay_interval);
	seq_printf(m, "Decays: %lld\n", ca->decays_done);

	seq_printf(m, "Action threshold: %lld\n", action_threshold);

	mutex_unlock(&ce_mutex);

	return 0;
}

static int array_open(struct inode *inode, struct file *filp)
{
	return single_open(filp, array_dump, NULL);
}

static const struct file_operations array_ops = {
	.owner	 = THIS_MODULE,
	.open	 = array_open,
	.read	 = seq_read,
	.llseek	 = seq_lseek,
	.release = single_release,
};

static int __init create_debugfs_nodes(void)
{
	struct dentry *d, *pfn, *decay, *count, *array;

	d = debugfs_create_dir("cec", ras_debugfs_dir);
	if (!d) {
		pr_warn("Error creating cec debugfs node!\n");
		return -1;
	}

	decay = debugfs_create_file("decay_interval", S_IRUSR | S_IWUSR, d,
				    &decay_interval, &decay_interval_ops);
	if (!decay) {
		pr_warn("Error creating decay_interval debugfs node!\n");
		goto err;
	}

	count = debugfs_create_file("action_threshold", S_IRUSR | S_IWUSR, d,
				    &action_threshold, &action_threshold_ops);
	if (!count) {
		pr_warn("Error creating action_threshold debugfs node!\n");
		goto err;
	}

	if (!IS_ENABLED(CONFIG_RAS_CEC_DEBUG))
		return 0;

	pfn = debugfs_create_file("pfn", S_IRUSR | S_IWUSR, d, &dfs_pfn, &pfn_ops);
	if (!pfn) {
		pr_warn("Error creating pfn debugfs node!\n");
		goto err;
	}

	array = debugfs_create_file("array", S_IRUSR, d, NULL, &array_ops);
	if (!array) {
		pr_warn("Error creating array debugfs node!\n");
		goto err;
	}

	return 0;

err:
	debugfs_remove_recursive(d);

	return 1;
}

void __init cec_init(void)
{
	if (ce_arr.disabled)
		return;

	ce_arr.array = (void *)get_zeroed_page(GFP_KERNEL);
	if (!ce_arr.array) {
		pr_err("Error allocating CE array page!\n");
		return;
	}

	if (create_debugfs_nodes()) {
		free_page((unsigned long)ce_arr.array);
		return;
	}

	INIT_DELAYED_WORK(&cec_work, cec_work_fn);
	schedule_delayed_work(&cec_work, CEC_DECAY_DEFAULT_INTERVAL);

	pr_info("Correctable Errors collector initialized.\n");
}

int __init parse_cec_param(char *str)
{
	if (!str)
		return 0;

	if (*str == '=')
		str++;

	if (!strcmp(str, "cec_disable"))
		ce_arr.disabled = 1;
	else
		return 0;

	return 1;
}