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
 94static 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
125static DEFINE_MUTEX(ce_mutex);
126static u64 dfs_pfn;
127
128/* Amount of errors after which we offline */
129static 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 */
135static struct delayed_work cec_work;
136static 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 */
142static 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 */
164static 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
172static 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 */
186static 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
223static 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
234static 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
245static 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 */
268static 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
283static 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 */
321static 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
391unlock:
392	mutex_unlock(&ce_mutex);
393
394	return ret;
395}
396
397static int u64_get(void *data, u64 *val)
398{
399	*val = *(u64 *)data;
400
401	return 0;
402}
403
404static int pfn_set(void *data, u64 val)
405{
406	*(u64 *)data = val;
407
408	cec_add_elem(val);
409
410	return 0;
411}
412
413DEFINE_DEBUGFS_ATTRIBUTE(pfn_ops, u64_get, pfn_set, "0x%llx\n");
414
415static 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}
430DEFINE_DEBUGFS_ATTRIBUTE(decay_interval_ops, u64_get, decay_interval_set, "%lld\n");
431
432static 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}
443DEFINE_DEBUGFS_ATTRIBUTE(action_threshold_ops, u64_get, action_threshold_set, "%lld\n");
444
445static const char * const bins[] = { "00", "01", "10", "11" };
446
447static 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
479DEFINE_SHOW_ATTRIBUTE(array);
480
481static 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
522err:
523	debugfs_remove_recursive(d);
524
525	return 1;
526}
527
528static 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
549static struct notifier_block cec_nb = {
550	.notifier_call	= cec_notifier,
551	.priority	= MCE_PRIO_CEC,
552};
553
554static 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}
586late_initcall(cec_init);
587
588int __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}