xref: /openbmc/linux/drivers/ras/cec.c (revision 6f52b16c5b29b89d92c0e7236f4655dc8491ad70)
1 // SPDX-License-Identifier: GPL-2.0
2 #include <linux/mm.h>
3 #include <linux/gfp.h>
4 #include <linux/kernel.h>
5 
6 #include <asm/mce.h>
7 
8 #include "debugfs.h"
9 
10 /*
11  * RAS Correctable Errors Collector
12  *
13  * This is a simple gadget which collects correctable errors and counts their
14  * occurrence per physical page address.
15  *
16  * We've opted for possibly the simplest data structure to collect those - an
17  * array of the size of a memory page. It stores 512 u64's with the following
18  * structure:
19  *
20  * [63 ... PFN ... 12 | 11 ... generation ... 10 | 9 ... count ... 0]
21  *
22  * The generation in the two highest order bits is two bits which are set to 11b
23  * on every insertion. During the course of each entry's existence, the
24  * generation field gets decremented during spring cleaning to 10b, then 01b and
25  * then 00b.
26  *
27  * This way we're employing the natural numeric ordering to make sure that newly
28  * inserted/touched elements have higher 12-bit counts (which we've manufactured)
29  * and thus iterating over the array initially won't kick out those elements
30  * which were inserted last.
31  *
32  * Spring cleaning is what we do when we reach a certain number CLEAN_ELEMS of
33  * elements entered into the array, during which, we're decaying all elements.
34  * If, after decay, an element gets inserted again, its generation is set to 11b
35  * to make sure it has higher numerical count than other, older elements and
36  * thus emulate an an LRU-like behavior when deleting elements to free up space
37  * in the page.
38  *
39  * When an element reaches it's max count of count_threshold, we try to poison
40  * it by assuming that errors triggered count_threshold times in a single page
41  * are excessive and that page shouldn't be used anymore. count_threshold is
42  * initialized to COUNT_MASK which is the maximum.
43  *
44  * That error event entry causes cec_add_elem() to return !0 value and thus
45  * signal to its callers to log the error.
46  *
47  * To the question why we've chosen a page and moving elements around with
48  * memmove(), it is because it is a very simple structure to handle and max data
49  * movement is 4K which on highly optimized modern CPUs is almost unnoticeable.
50  * We wanted to avoid the pointer traversal of more complex structures like a
51  * linked list or some sort of a balancing search tree.
52  *
53  * Deleting an element takes O(n) but since it is only a single page, it should
54  * be fast enough and it shouldn't happen all too often depending on error
55  * patterns.
56  */
57 
58 #undef pr_fmt
59 #define pr_fmt(fmt) "RAS: " fmt
60 
61 /*
62  * We use DECAY_BITS bits of PAGE_SHIFT bits for counting decay, i.e., how long
63  * elements have stayed in the array without having been accessed again.
64  */
65 #define DECAY_BITS		2
66 #define DECAY_MASK		((1ULL << DECAY_BITS) - 1)
67 #define MAX_ELEMS		(PAGE_SIZE / sizeof(u64))
68 
69 /*
70  * Threshold amount of inserted elements after which we start spring
71  * cleaning.
72  */
73 #define CLEAN_ELEMS		(MAX_ELEMS >> DECAY_BITS)
74 
75 /* Bits which count the number of errors happened in this 4K page. */
76 #define COUNT_BITS		(PAGE_SHIFT - DECAY_BITS)
77 #define COUNT_MASK		((1ULL << COUNT_BITS) - 1)
78 #define FULL_COUNT_MASK		(PAGE_SIZE - 1)
79 
80 /*
81  * u64: [ 63 ... 12 | DECAY_BITS | COUNT_BITS ]
82  */
83 
84 #define PFN(e)			((e) >> PAGE_SHIFT)
85 #define DECAY(e)		(((e) >> COUNT_BITS) & DECAY_MASK)
86 #define COUNT(e)		((unsigned int)(e) & COUNT_MASK)
87 #define FULL_COUNT(e)		((e) & (PAGE_SIZE - 1))
88 
89 static struct ce_array {
90 	u64 *array;			/* container page */
91 	unsigned int n;			/* number of elements in the array */
92 
93 	unsigned int decay_count;	/*
94 					 * number of element insertions/increments
95 					 * since the last spring cleaning.
96 					 */
97 
98 	u64 pfns_poisoned;		/*
99 					 * number of PFNs which got poisoned.
100 					 */
101 
102 	u64 ces_entered;		/*
103 					 * The number of correctable errors
104 					 * entered into the collector.
105 					 */
106 
107 	u64 decays_done;		/*
108 					 * Times we did spring cleaning.
109 					 */
110 
111 	union {
112 		struct {
113 			__u32	disabled : 1,	/* cmdline disabled */
114 			__resv   : 31;
115 		};
116 		__u32 flags;
117 	};
118 } ce_arr;
119 
120 static DEFINE_MUTEX(ce_mutex);
121 static u64 dfs_pfn;
122 
123 /* Amount of errors after which we offline */
124 static unsigned int count_threshold = COUNT_MASK;
125 
126 /*
127  * The timer "decays" element count each timer_interval which is 24hrs by
128  * default.
129  */
130 
131 #define CEC_TIMER_DEFAULT_INTERVAL	24 * 60 * 60	/* 24 hrs */
132 #define CEC_TIMER_MIN_INTERVAL		 1 * 60 * 60	/* 1h */
133 #define CEC_TIMER_MAX_INTERVAL	   30 *	24 * 60 * 60	/* one month */
134 static struct timer_list cec_timer;
135 static u64 timer_interval = CEC_TIMER_DEFAULT_INTERVAL;
136 
137 /*
138  * Decrement decay value. We're using DECAY_BITS bits to denote decay of an
139  * element in the array. On insertion and any access, it gets reset to max.
140  */
141 static void do_spring_cleaning(struct ce_array *ca)
142 {
143 	int i;
144 
145 	for (i = 0; i < ca->n; i++) {
146 		u8 decay = DECAY(ca->array[i]);
147 
148 		if (!decay)
149 			continue;
150 
151 		decay--;
152 
153 		ca->array[i] &= ~(DECAY_MASK << COUNT_BITS);
154 		ca->array[i] |= (decay << COUNT_BITS);
155 	}
156 	ca->decay_count = 0;
157 	ca->decays_done++;
158 }
159 
160 /*
161  * @interval in seconds
162  */
163 static void cec_mod_timer(struct timer_list *t, unsigned long interval)
164 {
165 	unsigned long iv;
166 
167 	iv = interval * HZ + jiffies;
168 
169 	mod_timer(t, round_jiffies(iv));
170 }
171 
172 static void cec_timer_fn(unsigned long data)
173 {
174 	struct ce_array *ca = (struct ce_array *)data;
175 
176 	do_spring_cleaning(ca);
177 
178 	cec_mod_timer(&cec_timer, timer_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  */
186 static int __find_elem(struct ce_array *ca, u64 pfn, unsigned int *to)
187 {
188 	u64 this_pfn;
189 	int min = 0, max = ca->n;
190 
191 	while (min < max) {
192 		int tmp = (max + min) >> 1;
193 
194 		this_pfn = PFN(ca->array[tmp]);
195 
196 		if (this_pfn < pfn)
197 			min = tmp + 1;
198 		else if (this_pfn > pfn)
199 			max = tmp;
200 		else {
201 			min = tmp;
202 			break;
203 		}
204 	}
205 
206 	if (to)
207 		*to = min;
208 
209 	this_pfn = PFN(ca->array[min]);
210 
211 	if (this_pfn == pfn)
212 		return min;
213 
214 	return -ENOKEY;
215 }
216 
217 static int find_elem(struct ce_array *ca, u64 pfn, unsigned int *to)
218 {
219 	WARN_ON(!to);
220 
221 	if (!ca->n) {
222 		*to = 0;
223 		return -ENOKEY;
224 	}
225 	return __find_elem(ca, pfn, to);
226 }
227 
228 static void del_elem(struct ce_array *ca, int idx)
229 {
230 	/* Save us a function call when deleting the last element. */
231 	if (ca->n - (idx + 1))
232 		memmove((void *)&ca->array[idx],
233 			(void *)&ca->array[idx + 1],
234 			(ca->n - (idx + 1)) * sizeof(u64));
235 
236 	ca->n--;
237 }
238 
239 static u64 del_lru_elem_unlocked(struct ce_array *ca)
240 {
241 	unsigned int min = FULL_COUNT_MASK;
242 	int i, min_idx = 0;
243 
244 	for (i = 0; i < ca->n; i++) {
245 		unsigned int this = FULL_COUNT(ca->array[i]);
246 
247 		if (min > this) {
248 			min = this;
249 			min_idx = i;
250 		}
251 	}
252 
253 	del_elem(ca, min_idx);
254 
255 	return PFN(ca->array[min_idx]);
256 }
257 
258 /*
259  * We return the 0th pfn in the error case under the assumption that it cannot
260  * be poisoned and excessive CEs in there are a serious deal anyway.
261  */
262 static u64 __maybe_unused del_lru_elem(void)
263 {
264 	struct ce_array *ca = &ce_arr;
265 	u64 pfn;
266 
267 	if (!ca->n)
268 		return 0;
269 
270 	mutex_lock(&ce_mutex);
271 	pfn = del_lru_elem_unlocked(ca);
272 	mutex_unlock(&ce_mutex);
273 
274 	return pfn;
275 }
276 
277 
278 int cec_add_elem(u64 pfn)
279 {
280 	struct ce_array *ca = &ce_arr;
281 	unsigned int to;
282 	int count, ret = 0;
283 
284 	/*
285 	 * We can be called very early on the identify_cpu() path where we are
286 	 * not initialized yet. We ignore the error for simplicity.
287 	 */
288 	if (!ce_arr.array || ce_arr.disabled)
289 		return -ENODEV;
290 
291 	ca->ces_entered++;
292 
293 	mutex_lock(&ce_mutex);
294 
295 	if (ca->n == MAX_ELEMS)
296 		WARN_ON(!del_lru_elem_unlocked(ca));
297 
298 	ret = find_elem(ca, pfn, &to);
299 	if (ret < 0) {
300 		/*
301 		 * Shift range [to-end] to make room for one more element.
302 		 */
303 		memmove((void *)&ca->array[to + 1],
304 			(void *)&ca->array[to],
305 			(ca->n - to) * sizeof(u64));
306 
307 		ca->array[to] = (pfn << PAGE_SHIFT) |
308 				(DECAY_MASK << COUNT_BITS) | 1;
309 
310 		ca->n++;
311 
312 		ret = 0;
313 
314 		goto decay;
315 	}
316 
317 	count = COUNT(ca->array[to]);
318 
319 	if (count < count_threshold) {
320 		ca->array[to] |= (DECAY_MASK << COUNT_BITS);
321 		ca->array[to]++;
322 
323 		ret = 0;
324 	} else {
325 		u64 pfn = ca->array[to] >> PAGE_SHIFT;
326 
327 		if (!pfn_valid(pfn)) {
328 			pr_warn("CEC: Invalid pfn: 0x%llx\n", pfn);
329 		} else {
330 			/* We have reached max count for this page, soft-offline it. */
331 			pr_err("Soft-offlining pfn: 0x%llx\n", pfn);
332 			memory_failure_queue(pfn, 0, MF_SOFT_OFFLINE);
333 			ca->pfns_poisoned++;
334 		}
335 
336 		del_elem(ca, to);
337 
338 		/*
339 		 * Return a >0 value to denote that we've reached the offlining
340 		 * threshold.
341 		 */
342 		ret = 1;
343 
344 		goto unlock;
345 	}
346 
347 decay:
348 	ca->decay_count++;
349 
350 	if (ca->decay_count >= CLEAN_ELEMS)
351 		do_spring_cleaning(ca);
352 
353 unlock:
354 	mutex_unlock(&ce_mutex);
355 
356 	return ret;
357 }
358 
359 static int u64_get(void *data, u64 *val)
360 {
361 	*val = *(u64 *)data;
362 
363 	return 0;
364 }
365 
366 static int pfn_set(void *data, u64 val)
367 {
368 	*(u64 *)data = val;
369 
370 	return cec_add_elem(val);
371 }
372 
373 DEFINE_DEBUGFS_ATTRIBUTE(pfn_ops, u64_get, pfn_set, "0x%llx\n");
374 
375 static int decay_interval_set(void *data, u64 val)
376 {
377 	*(u64 *)data = val;
378 
379 	if (val < CEC_TIMER_MIN_INTERVAL)
380 		return -EINVAL;
381 
382 	if (val > CEC_TIMER_MAX_INTERVAL)
383 		return -EINVAL;
384 
385 	timer_interval = val;
386 
387 	cec_mod_timer(&cec_timer, timer_interval);
388 	return 0;
389 }
390 DEFINE_DEBUGFS_ATTRIBUTE(decay_interval_ops, u64_get, decay_interval_set, "%lld\n");
391 
392 static int count_threshold_set(void *data, u64 val)
393 {
394 	*(u64 *)data = val;
395 
396 	if (val > COUNT_MASK)
397 		val = COUNT_MASK;
398 
399 	count_threshold = val;
400 
401 	return 0;
402 }
403 DEFINE_DEBUGFS_ATTRIBUTE(count_threshold_ops, u64_get, count_threshold_set, "%lld\n");
404 
405 static int array_dump(struct seq_file *m, void *v)
406 {
407 	struct ce_array *ca = &ce_arr;
408 	u64 prev = 0;
409 	int i;
410 
411 	mutex_lock(&ce_mutex);
412 
413 	seq_printf(m, "{ n: %d\n", ca->n);
414 	for (i = 0; i < ca->n; i++) {
415 		u64 this = PFN(ca->array[i]);
416 
417 		seq_printf(m, " %03d: [%016llx|%03llx]\n", i, this, FULL_COUNT(ca->array[i]));
418 
419 		WARN_ON(prev > this);
420 
421 		prev = this;
422 	}
423 
424 	seq_printf(m, "}\n");
425 
426 	seq_printf(m, "Stats:\nCEs: %llu\nofflined pages: %llu\n",
427 		   ca->ces_entered, ca->pfns_poisoned);
428 
429 	seq_printf(m, "Flags: 0x%x\n", ca->flags);
430 
431 	seq_printf(m, "Timer interval: %lld seconds\n", timer_interval);
432 	seq_printf(m, "Decays: %lld\n", ca->decays_done);
433 
434 	seq_printf(m, "Action threshold: %d\n", count_threshold);
435 
436 	mutex_unlock(&ce_mutex);
437 
438 	return 0;
439 }
440 
441 static int array_open(struct inode *inode, struct file *filp)
442 {
443 	return single_open(filp, array_dump, NULL);
444 }
445 
446 static const struct file_operations array_ops = {
447 	.owner	 = THIS_MODULE,
448 	.open	 = array_open,
449 	.read	 = seq_read,
450 	.llseek	 = seq_lseek,
451 	.release = single_release,
452 };
453 
454 static int __init create_debugfs_nodes(void)
455 {
456 	struct dentry *d, *pfn, *decay, *count, *array;
457 
458 	d = debugfs_create_dir("cec", ras_debugfs_dir);
459 	if (!d) {
460 		pr_warn("Error creating cec debugfs node!\n");
461 		return -1;
462 	}
463 
464 	pfn = debugfs_create_file("pfn", S_IRUSR | S_IWUSR, d, &dfs_pfn, &pfn_ops);
465 	if (!pfn) {
466 		pr_warn("Error creating pfn debugfs node!\n");
467 		goto err;
468 	}
469 
470 	array = debugfs_create_file("array", S_IRUSR, d, NULL, &array_ops);
471 	if (!array) {
472 		pr_warn("Error creating array debugfs node!\n");
473 		goto err;
474 	}
475 
476 	decay = debugfs_create_file("decay_interval", S_IRUSR | S_IWUSR, d,
477 				    &timer_interval, &decay_interval_ops);
478 	if (!decay) {
479 		pr_warn("Error creating decay_interval debugfs node!\n");
480 		goto err;
481 	}
482 
483 	count = debugfs_create_file("count_threshold", S_IRUSR | S_IWUSR, d,
484 				    &count_threshold, &count_threshold_ops);
485 	if (!count) {
486 		pr_warn("Error creating count_threshold debugfs node!\n");
487 		goto err;
488 	}
489 
490 
491 	return 0;
492 
493 err:
494 	debugfs_remove_recursive(d);
495 
496 	return 1;
497 }
498 
499 void __init cec_init(void)
500 {
501 	if (ce_arr.disabled)
502 		return;
503 
504 	ce_arr.array = (void *)get_zeroed_page(GFP_KERNEL);
505 	if (!ce_arr.array) {
506 		pr_err("Error allocating CE array page!\n");
507 		return;
508 	}
509 
510 	if (create_debugfs_nodes())
511 		return;
512 
513 	setup_timer(&cec_timer, cec_timer_fn, (unsigned long)&ce_arr);
514 	cec_mod_timer(&cec_timer, CEC_TIMER_DEFAULT_INTERVAL);
515 
516 	pr_info("Correctable Errors collector initialized.\n");
517 }
518 
519 int __init parse_cec_param(char *str)
520 {
521 	if (!str)
522 		return 0;
523 
524 	if (*str == '=')
525 		str++;
526 
527 	if (!strcmp(str, "cec_disable"))
528 		ce_arr.disabled = 1;
529 	else
530 		return 0;
531 
532 	return 1;
533 }
534