1 // SPDX-License-Identifier: GPL-2.0 2 /* 3 * Request reply cache. This is currently a global cache, but this may 4 * change in the future and be a per-client cache. 5 * 6 * This code is heavily inspired by the 44BSD implementation, although 7 * it does things a bit differently. 8 * 9 * Copyright (C) 1995, 1996 Olaf Kirch <okir@monad.swb.de> 10 */ 11 12 #include <linux/slab.h> 13 #include <linux/vmalloc.h> 14 #include <linux/sunrpc/addr.h> 15 #include <linux/highmem.h> 16 #include <linux/log2.h> 17 #include <linux/hash.h> 18 #include <net/checksum.h> 19 20 #include "nfsd.h" 21 #include "cache.h" 22 23 #define NFSDDBG_FACILITY NFSDDBG_REPCACHE 24 25 /* 26 * We use this value to determine the number of hash buckets from the max 27 * cache size, the idea being that when the cache is at its maximum number 28 * of entries, then this should be the average number of entries per bucket. 29 */ 30 #define TARGET_BUCKET_SIZE 64 31 32 struct nfsd_drc_bucket { 33 struct rb_root rb_head; 34 struct list_head lru_head; 35 spinlock_t cache_lock; 36 }; 37 38 static struct nfsd_drc_bucket *drc_hashtbl; 39 static struct kmem_cache *drc_slab; 40 41 /* max number of entries allowed in the cache */ 42 static unsigned int max_drc_entries; 43 44 /* number of significant bits in the hash value */ 45 static unsigned int maskbits; 46 static unsigned int drc_hashsize; 47 48 /* 49 * Stats and other tracking of on the duplicate reply cache. All of these and 50 * the "rc" fields in nfsdstats are protected by the cache_lock 51 */ 52 53 /* total number of entries */ 54 static atomic_t num_drc_entries; 55 56 /* cache misses due only to checksum comparison failures */ 57 static unsigned int payload_misses; 58 59 /* amount of memory (in bytes) currently consumed by the DRC */ 60 static unsigned int drc_mem_usage; 61 62 /* longest hash chain seen */ 63 static unsigned int longest_chain; 64 65 /* size of cache when we saw the longest hash chain */ 66 static unsigned int longest_chain_cachesize; 67 68 static int nfsd_cache_append(struct svc_rqst *rqstp, struct kvec *vec); 69 static unsigned long nfsd_reply_cache_count(struct shrinker *shrink, 70 struct shrink_control *sc); 71 static unsigned long nfsd_reply_cache_scan(struct shrinker *shrink, 72 struct shrink_control *sc); 73 74 static struct shrinker nfsd_reply_cache_shrinker = { 75 .scan_objects = nfsd_reply_cache_scan, 76 .count_objects = nfsd_reply_cache_count, 77 .seeks = 1, 78 }; 79 80 /* 81 * Put a cap on the size of the DRC based on the amount of available 82 * low memory in the machine. 83 * 84 * 64MB: 8192 85 * 128MB: 11585 86 * 256MB: 16384 87 * 512MB: 23170 88 * 1GB: 32768 89 * 2GB: 46340 90 * 4GB: 65536 91 * 8GB: 92681 92 * 16GB: 131072 93 * 94 * ...with a hard cap of 256k entries. In the worst case, each entry will be 95 * ~1k, so the above numbers should give a rough max of the amount of memory 96 * used in k. 97 */ 98 static unsigned int 99 nfsd_cache_size_limit(void) 100 { 101 unsigned int limit; 102 unsigned long low_pages = totalram_pages() - totalhigh_pages(); 103 104 limit = (16 * int_sqrt(low_pages)) << (PAGE_SHIFT-10); 105 return min_t(unsigned int, limit, 256*1024); 106 } 107 108 /* 109 * Compute the number of hash buckets we need. Divide the max cachesize by 110 * the "target" max bucket size, and round up to next power of two. 111 */ 112 static unsigned int 113 nfsd_hashsize(unsigned int limit) 114 { 115 return roundup_pow_of_two(limit / TARGET_BUCKET_SIZE); 116 } 117 118 static u32 119 nfsd_cache_hash(__be32 xid) 120 { 121 return hash_32(be32_to_cpu(xid), maskbits); 122 } 123 124 static struct svc_cacherep * 125 nfsd_reply_cache_alloc(struct svc_rqst *rqstp, __wsum csum) 126 { 127 struct svc_cacherep *rp; 128 129 rp = kmem_cache_alloc(drc_slab, GFP_KERNEL); 130 if (rp) { 131 rp->c_state = RC_UNUSED; 132 rp->c_type = RC_NOCACHE; 133 RB_CLEAR_NODE(&rp->c_node); 134 INIT_LIST_HEAD(&rp->c_lru); 135 136 memset(&rp->c_key, 0, sizeof(rp->c_key)); 137 rp->c_key.k_xid = rqstp->rq_xid; 138 rp->c_key.k_proc = rqstp->rq_proc; 139 rpc_copy_addr((struct sockaddr *)&rp->c_key.k_addr, svc_addr(rqstp)); 140 rpc_set_port((struct sockaddr *)&rp->c_key.k_addr, rpc_get_port(svc_addr(rqstp))); 141 rp->c_key.k_prot = rqstp->rq_prot; 142 rp->c_key.k_vers = rqstp->rq_vers; 143 rp->c_key.k_len = rqstp->rq_arg.len; 144 rp->c_key.k_csum = csum; 145 } 146 return rp; 147 } 148 149 static void 150 nfsd_reply_cache_free_locked(struct nfsd_drc_bucket *b, struct svc_cacherep *rp) 151 { 152 if (rp->c_type == RC_REPLBUFF && rp->c_replvec.iov_base) { 153 drc_mem_usage -= rp->c_replvec.iov_len; 154 kfree(rp->c_replvec.iov_base); 155 } 156 if (rp->c_state != RC_UNUSED) { 157 rb_erase(&rp->c_node, &b->rb_head); 158 list_del(&rp->c_lru); 159 atomic_dec(&num_drc_entries); 160 drc_mem_usage -= sizeof(*rp); 161 } 162 kmem_cache_free(drc_slab, rp); 163 } 164 165 static void 166 nfsd_reply_cache_free(struct nfsd_drc_bucket *b, struct svc_cacherep *rp) 167 { 168 spin_lock(&b->cache_lock); 169 nfsd_reply_cache_free_locked(b, rp); 170 spin_unlock(&b->cache_lock); 171 } 172 173 int nfsd_reply_cache_init(void) 174 { 175 unsigned int hashsize; 176 unsigned int i; 177 int status = 0; 178 179 max_drc_entries = nfsd_cache_size_limit(); 180 atomic_set(&num_drc_entries, 0); 181 hashsize = nfsd_hashsize(max_drc_entries); 182 maskbits = ilog2(hashsize); 183 184 status = register_shrinker(&nfsd_reply_cache_shrinker); 185 if (status) 186 return status; 187 188 drc_slab = kmem_cache_create("nfsd_drc", sizeof(struct svc_cacherep), 189 0, 0, NULL); 190 if (!drc_slab) 191 goto out_nomem; 192 193 drc_hashtbl = kcalloc(hashsize, sizeof(*drc_hashtbl), GFP_KERNEL); 194 if (!drc_hashtbl) { 195 drc_hashtbl = vzalloc(array_size(hashsize, 196 sizeof(*drc_hashtbl))); 197 if (!drc_hashtbl) 198 goto out_nomem; 199 } 200 201 for (i = 0; i < hashsize; i++) { 202 INIT_LIST_HEAD(&drc_hashtbl[i].lru_head); 203 spin_lock_init(&drc_hashtbl[i].cache_lock); 204 } 205 drc_hashsize = hashsize; 206 207 return 0; 208 out_nomem: 209 printk(KERN_ERR "nfsd: failed to allocate reply cache\n"); 210 nfsd_reply_cache_shutdown(); 211 return -ENOMEM; 212 } 213 214 void nfsd_reply_cache_shutdown(void) 215 { 216 struct svc_cacherep *rp; 217 unsigned int i; 218 219 unregister_shrinker(&nfsd_reply_cache_shrinker); 220 221 for (i = 0; i < drc_hashsize; i++) { 222 struct list_head *head = &drc_hashtbl[i].lru_head; 223 while (!list_empty(head)) { 224 rp = list_first_entry(head, struct svc_cacherep, c_lru); 225 nfsd_reply_cache_free_locked(&drc_hashtbl[i], rp); 226 } 227 } 228 229 kvfree(drc_hashtbl); 230 drc_hashtbl = NULL; 231 drc_hashsize = 0; 232 233 kmem_cache_destroy(drc_slab); 234 drc_slab = NULL; 235 } 236 237 /* 238 * Move cache entry to end of LRU list, and queue the cleaner to run if it's 239 * not already scheduled. 240 */ 241 static void 242 lru_put_end(struct nfsd_drc_bucket *b, struct svc_cacherep *rp) 243 { 244 rp->c_timestamp = jiffies; 245 list_move_tail(&rp->c_lru, &b->lru_head); 246 } 247 248 static long 249 prune_bucket(struct nfsd_drc_bucket *b) 250 { 251 struct svc_cacherep *rp, *tmp; 252 long freed = 0; 253 254 list_for_each_entry_safe(rp, tmp, &b->lru_head, c_lru) { 255 /* 256 * Don't free entries attached to calls that are still 257 * in-progress, but do keep scanning the list. 258 */ 259 if (rp->c_state == RC_INPROG) 260 continue; 261 if (atomic_read(&num_drc_entries) <= max_drc_entries && 262 time_before(jiffies, rp->c_timestamp + RC_EXPIRE)) 263 break; 264 nfsd_reply_cache_free_locked(b, rp); 265 freed++; 266 } 267 return freed; 268 } 269 270 /* 271 * Walk the LRU list and prune off entries that are older than RC_EXPIRE. 272 * Also prune the oldest ones when the total exceeds the max number of entries. 273 */ 274 static long 275 prune_cache_entries(void) 276 { 277 unsigned int i; 278 long freed = 0; 279 280 for (i = 0; i < drc_hashsize; i++) { 281 struct nfsd_drc_bucket *b = &drc_hashtbl[i]; 282 283 if (list_empty(&b->lru_head)) 284 continue; 285 spin_lock(&b->cache_lock); 286 freed += prune_bucket(b); 287 spin_unlock(&b->cache_lock); 288 } 289 return freed; 290 } 291 292 static unsigned long 293 nfsd_reply_cache_count(struct shrinker *shrink, struct shrink_control *sc) 294 { 295 return atomic_read(&num_drc_entries); 296 } 297 298 static unsigned long 299 nfsd_reply_cache_scan(struct shrinker *shrink, struct shrink_control *sc) 300 { 301 return prune_cache_entries(); 302 } 303 /* 304 * Walk an xdr_buf and get a CRC for at most the first RC_CSUMLEN bytes 305 */ 306 static __wsum 307 nfsd_cache_csum(struct svc_rqst *rqstp) 308 { 309 int idx; 310 unsigned int base; 311 __wsum csum; 312 struct xdr_buf *buf = &rqstp->rq_arg; 313 const unsigned char *p = buf->head[0].iov_base; 314 size_t csum_len = min_t(size_t, buf->head[0].iov_len + buf->page_len, 315 RC_CSUMLEN); 316 size_t len = min(buf->head[0].iov_len, csum_len); 317 318 /* rq_arg.head first */ 319 csum = csum_partial(p, len, 0); 320 csum_len -= len; 321 322 /* Continue into page array */ 323 idx = buf->page_base / PAGE_SIZE; 324 base = buf->page_base & ~PAGE_MASK; 325 while (csum_len) { 326 p = page_address(buf->pages[idx]) + base; 327 len = min_t(size_t, PAGE_SIZE - base, csum_len); 328 csum = csum_partial(p, len, csum); 329 csum_len -= len; 330 base = 0; 331 ++idx; 332 } 333 return csum; 334 } 335 336 static int 337 nfsd_cache_key_cmp(const struct svc_cacherep *key, const struct svc_cacherep *rp) 338 { 339 if (key->c_key.k_xid == rp->c_key.k_xid && 340 key->c_key.k_csum != rp->c_key.k_csum) 341 ++payload_misses; 342 343 return memcmp(&key->c_key, &rp->c_key, sizeof(key->c_key)); 344 } 345 346 /* 347 * Search the request hash for an entry that matches the given rqstp. 348 * Must be called with cache_lock held. Returns the found entry or 349 * inserts an empty key on failure. 350 */ 351 static struct svc_cacherep * 352 nfsd_cache_insert(struct nfsd_drc_bucket *b, struct svc_cacherep *key) 353 { 354 struct svc_cacherep *rp, *ret = key; 355 struct rb_node **p = &b->rb_head.rb_node, 356 *parent = NULL; 357 unsigned int entries = 0; 358 int cmp; 359 360 while (*p != NULL) { 361 ++entries; 362 parent = *p; 363 rp = rb_entry(parent, struct svc_cacherep, c_node); 364 365 cmp = nfsd_cache_key_cmp(key, rp); 366 if (cmp < 0) 367 p = &parent->rb_left; 368 else if (cmp > 0) 369 p = &parent->rb_right; 370 else { 371 ret = rp; 372 goto out; 373 } 374 } 375 rb_link_node(&key->c_node, parent, p); 376 rb_insert_color(&key->c_node, &b->rb_head); 377 out: 378 /* tally hash chain length stats */ 379 if (entries > longest_chain) { 380 longest_chain = entries; 381 longest_chain_cachesize = atomic_read(&num_drc_entries); 382 } else if (entries == longest_chain) { 383 /* prefer to keep the smallest cachesize possible here */ 384 longest_chain_cachesize = min_t(unsigned int, 385 longest_chain_cachesize, 386 atomic_read(&num_drc_entries)); 387 } 388 389 lru_put_end(b, ret); 390 return ret; 391 } 392 393 /* 394 * Try to find an entry matching the current call in the cache. When none 395 * is found, we try to grab the oldest expired entry off the LRU list. If 396 * a suitable one isn't there, then drop the cache_lock and allocate a 397 * new one, then search again in case one got inserted while this thread 398 * didn't hold the lock. 399 */ 400 int 401 nfsd_cache_lookup(struct svc_rqst *rqstp) 402 { 403 struct svc_cacherep *rp, *found; 404 __be32 xid = rqstp->rq_xid; 405 __wsum csum; 406 u32 hash = nfsd_cache_hash(xid); 407 struct nfsd_drc_bucket *b = &drc_hashtbl[hash]; 408 int type = rqstp->rq_cachetype; 409 int rtn = RC_DOIT; 410 411 rqstp->rq_cacherep = NULL; 412 if (type == RC_NOCACHE) { 413 nfsdstats.rcnocache++; 414 return rtn; 415 } 416 417 csum = nfsd_cache_csum(rqstp); 418 419 /* 420 * Since the common case is a cache miss followed by an insert, 421 * preallocate an entry. 422 */ 423 rp = nfsd_reply_cache_alloc(rqstp, csum); 424 if (!rp) { 425 dprintk("nfsd: unable to allocate DRC entry!\n"); 426 return rtn; 427 } 428 429 spin_lock(&b->cache_lock); 430 found = nfsd_cache_insert(b, rp); 431 if (found != rp) { 432 nfsd_reply_cache_free_locked(NULL, rp); 433 rp = found; 434 goto found_entry; 435 } 436 437 nfsdstats.rcmisses++; 438 rqstp->rq_cacherep = rp; 439 rp->c_state = RC_INPROG; 440 441 atomic_inc(&num_drc_entries); 442 drc_mem_usage += sizeof(*rp); 443 444 /* go ahead and prune the cache */ 445 prune_bucket(b); 446 out: 447 spin_unlock(&b->cache_lock); 448 return rtn; 449 450 found_entry: 451 /* We found a matching entry which is either in progress or done. */ 452 nfsdstats.rchits++; 453 rtn = RC_DROPIT; 454 455 /* Request being processed */ 456 if (rp->c_state == RC_INPROG) 457 goto out; 458 459 /* From the hall of fame of impractical attacks: 460 * Is this a user who tries to snoop on the cache? */ 461 rtn = RC_DOIT; 462 if (!test_bit(RQ_SECURE, &rqstp->rq_flags) && rp->c_secure) 463 goto out; 464 465 /* Compose RPC reply header */ 466 switch (rp->c_type) { 467 case RC_NOCACHE: 468 break; 469 case RC_REPLSTAT: 470 svc_putu32(&rqstp->rq_res.head[0], rp->c_replstat); 471 rtn = RC_REPLY; 472 break; 473 case RC_REPLBUFF: 474 if (!nfsd_cache_append(rqstp, &rp->c_replvec)) 475 goto out; /* should not happen */ 476 rtn = RC_REPLY; 477 break; 478 default: 479 printk(KERN_WARNING "nfsd: bad repcache type %d\n", rp->c_type); 480 nfsd_reply_cache_free_locked(b, rp); 481 } 482 483 goto out; 484 } 485 486 /* 487 * Update a cache entry. This is called from nfsd_dispatch when 488 * the procedure has been executed and the complete reply is in 489 * rqstp->rq_res. 490 * 491 * We're copying around data here rather than swapping buffers because 492 * the toplevel loop requires max-sized buffers, which would be a waste 493 * of memory for a cache with a max reply size of 100 bytes (diropokres). 494 * 495 * If we should start to use different types of cache entries tailored 496 * specifically for attrstat and fh's, we may save even more space. 497 * 498 * Also note that a cachetype of RC_NOCACHE can legally be passed when 499 * nfsd failed to encode a reply that otherwise would have been cached. 500 * In this case, nfsd_cache_update is called with statp == NULL. 501 */ 502 void 503 nfsd_cache_update(struct svc_rqst *rqstp, int cachetype, __be32 *statp) 504 { 505 struct svc_cacherep *rp = rqstp->rq_cacherep; 506 struct kvec *resv = &rqstp->rq_res.head[0], *cachv; 507 u32 hash; 508 struct nfsd_drc_bucket *b; 509 int len; 510 size_t bufsize = 0; 511 512 if (!rp) 513 return; 514 515 hash = nfsd_cache_hash(rp->c_key.k_xid); 516 b = &drc_hashtbl[hash]; 517 518 len = resv->iov_len - ((char*)statp - (char*)resv->iov_base); 519 len >>= 2; 520 521 /* Don't cache excessive amounts of data and XDR failures */ 522 if (!statp || len > (256 >> 2)) { 523 nfsd_reply_cache_free(b, rp); 524 return; 525 } 526 527 switch (cachetype) { 528 case RC_REPLSTAT: 529 if (len != 1) 530 printk("nfsd: RC_REPLSTAT/reply len %d!\n",len); 531 rp->c_replstat = *statp; 532 break; 533 case RC_REPLBUFF: 534 cachv = &rp->c_replvec; 535 bufsize = len << 2; 536 cachv->iov_base = kmalloc(bufsize, GFP_KERNEL); 537 if (!cachv->iov_base) { 538 nfsd_reply_cache_free(b, rp); 539 return; 540 } 541 cachv->iov_len = bufsize; 542 memcpy(cachv->iov_base, statp, bufsize); 543 break; 544 case RC_NOCACHE: 545 nfsd_reply_cache_free(b, rp); 546 return; 547 } 548 spin_lock(&b->cache_lock); 549 drc_mem_usage += bufsize; 550 lru_put_end(b, rp); 551 rp->c_secure = test_bit(RQ_SECURE, &rqstp->rq_flags); 552 rp->c_type = cachetype; 553 rp->c_state = RC_DONE; 554 spin_unlock(&b->cache_lock); 555 return; 556 } 557 558 /* 559 * Copy cached reply to current reply buffer. Should always fit. 560 * FIXME as reply is in a page, we should just attach the page, and 561 * keep a refcount.... 562 */ 563 static int 564 nfsd_cache_append(struct svc_rqst *rqstp, struct kvec *data) 565 { 566 struct kvec *vec = &rqstp->rq_res.head[0]; 567 568 if (vec->iov_len + data->iov_len > PAGE_SIZE) { 569 printk(KERN_WARNING "nfsd: cached reply too large (%zd).\n", 570 data->iov_len); 571 return 0; 572 } 573 memcpy((char*)vec->iov_base + vec->iov_len, data->iov_base, data->iov_len); 574 vec->iov_len += data->iov_len; 575 return 1; 576 } 577 578 /* 579 * Note that fields may be added, removed or reordered in the future. Programs 580 * scraping this file for info should test the labels to ensure they're 581 * getting the correct field. 582 */ 583 static int nfsd_reply_cache_stats_show(struct seq_file *m, void *v) 584 { 585 seq_printf(m, "max entries: %u\n", max_drc_entries); 586 seq_printf(m, "num entries: %u\n", 587 atomic_read(&num_drc_entries)); 588 seq_printf(m, "hash buckets: %u\n", 1 << maskbits); 589 seq_printf(m, "mem usage: %u\n", drc_mem_usage); 590 seq_printf(m, "cache hits: %u\n", nfsdstats.rchits); 591 seq_printf(m, "cache misses: %u\n", nfsdstats.rcmisses); 592 seq_printf(m, "not cached: %u\n", nfsdstats.rcnocache); 593 seq_printf(m, "payload misses: %u\n", payload_misses); 594 seq_printf(m, "longest chain len: %u\n", longest_chain); 595 seq_printf(m, "cachesize at longest: %u\n", longest_chain_cachesize); 596 return 0; 597 } 598 599 int nfsd_reply_cache_stats_open(struct inode *inode, struct file *file) 600 { 601 return single_open(file, nfsd_reply_cache_stats_show, NULL); 602 } 603