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