root/drivers/ras/cec.c

DEFINITIONS

1. do_spring_cleaning
2. cec_mod_work
3. cec_work_fn
4. __find_elem
5. find_elem
6. del_elem
7. del_lru_elem_unlocked
8. del_lru_elem
9. sanity_check
10. cec_add_elem
11. u64_get
12. pfn_set
13. decay_interval_set
14. action_threshold_set
15. array_dump
16. array_open
17. create_debugfs_nodes
18. cec_init
19. parse_cec_param

   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 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  */
 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  */
 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 
 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  */
 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 
 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 
 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 
 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  */
 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 
 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 int cec_add_elem(u64 pfn)
 313 {
 314         struct ce_array *ca = &ce_arr;
 315         unsigned int to = 0;
 316         int count, ret = 0;
 317 
 318         /*
 319          * We can be called very early on the identify_cpu() path where we are
 320          * not initialized yet. We ignore the error for simplicity.
 321          */
 322         if (!ce_arr.array || ce_arr.disabled)
 323                 return -ENODEV;
 324 
 325         mutex_lock(&ce_mutex);
 326 
 327         ca->ces_entered++;
 328 
 329         /* Array full, free the LRU slot. */
 330         if (ca->n == MAX_ELEMS)
 331                 WARN_ON(!del_lru_elem_unlocked(ca));
 332 
 333         ret = find_elem(ca, pfn, &to);
 334         if (ret < 0) {
 335                 /*
 336                  * Shift range [to-end] to make room for one more element.
 337                  */
 338                 memmove((void *)&ca->array[to + 1],
 339                         (void *)&ca->array[to],
 340                         (ca->n - to) * sizeof(u64));
 341 
 342                 ca->array[to] = pfn << PAGE_SHIFT;
 343                 ca->n++;
 344         }
 345 
 346         /* Add/refresh element generation and increment count */
 347         ca->array[to] |= DECAY_MASK << COUNT_BITS;
 348         ca->array[to]++;
 349 
 350         /* Check action threshold and soft-offline, if reached. */
 351         count = COUNT(ca->array[to]);
 352         if (count >= action_threshold) {
 353                 u64 pfn = ca->array[to] >> PAGE_SHIFT;
 354 
 355                 if (!pfn_valid(pfn)) {
 356                         pr_warn("CEC: Invalid pfn: 0x%llx\n", pfn);
 357                 } else {
 358                         /* We have reached max count for this page, soft-offline it. */
 359                         pr_err("Soft-offlining pfn: 0x%llx\n", pfn);
 360                         memory_failure_queue(pfn, MF_SOFT_OFFLINE);
 361                         ca->pfns_poisoned++;
 362                 }
 363 
 364                 del_elem(ca, to);
 365 
 366                 /*
 367                  * Return a >0 value to callers, to denote that we've reached
 368                  * the offlining threshold.
 369                  */
 370                 ret = 1;
 371 
 372                 goto unlock;
 373         }
 374 
 375         ca->decay_count++;
 376 
 377         if (ca->decay_count >= CLEAN_ELEMS)
 378                 do_spring_cleaning(ca);
 379 
 380         WARN_ON_ONCE(sanity_check(ca));
 381 
 382 unlock:
 383         mutex_unlock(&ce_mutex);
 384 
 385         return ret;
 386 }
 387 
 388 static int u64_get(void *data, u64 *val)
 389 {
 390         *val = *(u64 *)data;
 391 
 392         return 0;
 393 }
 394 
 395 static int pfn_set(void *data, u64 val)
 396 {
 397         *(u64 *)data = val;
 398 
 399         cec_add_elem(val);
 400 
 401         return 0;
 402 }
 403 
 404 DEFINE_DEBUGFS_ATTRIBUTE(pfn_ops, u64_get, pfn_set, "0x%llx\n");
 405 
 406 static int decay_interval_set(void *data, u64 val)
 407 {
 408         if (val < CEC_DECAY_MIN_INTERVAL)
 409                 return -EINVAL;
 410 
 411         if (val > CEC_DECAY_MAX_INTERVAL)
 412                 return -EINVAL;
 413 
 414         *(u64 *)data   = val;
 415         decay_interval = val;
 416 
 417         cec_mod_work(decay_interval);
 418 
 419         return 0;
 420 }
 421 DEFINE_DEBUGFS_ATTRIBUTE(decay_interval_ops, u64_get, decay_interval_set, "%lld\n");
 422 
 423 static int action_threshold_set(void *data, u64 val)
 424 {
 425         *(u64 *)data = val;
 426 
 427         if (val > COUNT_MASK)
 428                 val = COUNT_MASK;
 429 
 430         action_threshold = val;
 431 
 432         return 0;
 433 }
 434 DEFINE_DEBUGFS_ATTRIBUTE(action_threshold_ops, u64_get, action_threshold_set, "%lld\n");
 435 
 436 static const char * const bins[] = { "00", "01", "10", "11" };
 437 
 438 static int array_dump(struct seq_file *m, void *v)
 439 {
 440         struct ce_array *ca = &ce_arr;
 441         int i;
 442 
 443         mutex_lock(&ce_mutex);
 444 
 445         seq_printf(m, "{ n: %d\n", ca->n);
 446         for (i = 0; i < ca->n; i++) {
 447                 u64 this = PFN(ca->array[i]);
 448 
 449                 seq_printf(m, " %3d: [%016llx|%s|%03llx]\n",
 450                            i, this, bins[DECAY(ca->array[i])], COUNT(ca->array[i]));
 451         }
 452 
 453         seq_printf(m, "}\n");
 454 
 455         seq_printf(m, "Stats:\nCEs: %llu\nofflined pages: %llu\n",
 456                    ca->ces_entered, ca->pfns_poisoned);
 457 
 458         seq_printf(m, "Flags: 0x%x\n", ca->flags);
 459 
 460         seq_printf(m, "Decay interval: %lld seconds\n", decay_interval);
 461         seq_printf(m, "Decays: %lld\n", ca->decays_done);
 462 
 463         seq_printf(m, "Action threshold: %lld\n", action_threshold);
 464 
 465         mutex_unlock(&ce_mutex);
 466 
 467         return 0;
 468 }
 469 
 470 static int array_open(struct inode *inode, struct file *filp)
 471 {
 472         return single_open(filp, array_dump, NULL);
 473 }
 474 
 475 static const struct file_operations array_ops = {
 476         .owner   = THIS_MODULE,
 477         .open    = array_open,
 478         .read    = seq_read,
 479         .llseek  = seq_lseek,
 480         .release = single_release,
 481 };
 482 
 483 static int __init create_debugfs_nodes(void)
 484 {
 485         struct dentry *d, *pfn, *decay, *count, *array;
 486 
 487         d = debugfs_create_dir("cec", ras_debugfs_dir);
 488         if (!d) {
 489                 pr_warn("Error creating cec debugfs node!\n");
 490                 return -1;
 491         }
 492 
 493         decay = debugfs_create_file("decay_interval", S_IRUSR | S_IWUSR, d,
 494                                     &decay_interval, &decay_interval_ops);
 495         if (!decay) {
 496                 pr_warn("Error creating decay_interval debugfs node!\n");
 497                 goto err;
 498         }
 499 
 500         count = debugfs_create_file("action_threshold", S_IRUSR | S_IWUSR, d,
 501                                     &action_threshold, &action_threshold_ops);
 502         if (!count) {
 503                 pr_warn("Error creating action_threshold debugfs node!\n");
 504                 goto err;
 505         }
 506 
 507         if (!IS_ENABLED(CONFIG_RAS_CEC_DEBUG))
 508                 return 0;
 509 
 510         pfn = debugfs_create_file("pfn", S_IRUSR | S_IWUSR, d, &dfs_pfn, &pfn_ops);
 511         if (!pfn) {
 512                 pr_warn("Error creating pfn debugfs node!\n");
 513                 goto err;
 514         }
 515 
 516         array = debugfs_create_file("array", S_IRUSR, d, NULL, &array_ops);
 517         if (!array) {
 518                 pr_warn("Error creating array debugfs node!\n");
 519                 goto err;
 520         }
 521 
 522         return 0;
 523 
 524 err:
 525         debugfs_remove_recursive(d);
 526 
 527         return 1;
 528 }
 529 
 530 void __init cec_init(void)
 531 {
 532         if (ce_arr.disabled)
 533                 return;
 534 
 535         ce_arr.array = (void *)get_zeroed_page(GFP_KERNEL);
 536         if (!ce_arr.array) {
 537                 pr_err("Error allocating CE array page!\n");
 538                 return;
 539         }
 540 
 541         if (create_debugfs_nodes()) {
 542                 free_page((unsigned long)ce_arr.array);
 543                 return;
 544         }
 545 
 546         INIT_DELAYED_WORK(&cec_work, cec_work_fn);
 547         schedule_delayed_work(&cec_work, CEC_DECAY_DEFAULT_INTERVAL);
 548 
 549         pr_info("Correctable Errors collector initialized.\n");
 550 }
 551 
 552 int __init parse_cec_param(char *str)
 553 {
 554         if (!str)
 555                 return 0;
 556 
 557         if (*str == '=')
 558                 str++;
 559 
 560         if (!strcmp(str, "cec_disable"))
 561                 ce_arr.disabled = 1;
 562         else
 563                 return 0;
 564 
 565         return 1;
 566 }