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 list_head lru_head;
34 	spinlock_t cache_lock;
35 };
36 
37 static struct nfsd_drc_bucket	*drc_hashtbl;
38 static struct kmem_cache	*drc_slab;
39 
40 /* max number of entries allowed in the cache */
41 static unsigned int		max_drc_entries;
42 
43 /* number of significant bits in the hash value */
44 static unsigned int		maskbits;
45 static unsigned int		drc_hashsize;
46 
47 /*
48  * Stats and other tracking of on the duplicate reply cache. All of these and
49  * the "rc" fields in nfsdstats are protected by the cache_lock
50  */
51 
52 /* total number of entries */
53 static atomic_t			num_drc_entries;
54 
55 /* cache misses due only to checksum comparison failures */
56 static unsigned int		payload_misses;
57 
58 /* amount of memory (in bytes) currently consumed by the DRC */
59 static unsigned int		drc_mem_usage;
60 
61 /* longest hash chain seen */
62 static unsigned int		longest_chain;
63 
64 /* size of cache when we saw the longest hash chain */
65 static unsigned int		longest_chain_cachesize;
66 
67 static int	nfsd_cache_append(struct svc_rqst *rqstp, struct kvec *vec);
68 static unsigned long nfsd_reply_cache_count(struct shrinker *shrink,
69 					    struct shrink_control *sc);
70 static unsigned long nfsd_reply_cache_scan(struct shrinker *shrink,
71 					   struct shrink_control *sc);
72 
73 static struct shrinker nfsd_reply_cache_shrinker = {
74 	.scan_objects = nfsd_reply_cache_scan,
75 	.count_objects = nfsd_reply_cache_count,
76 	.seeks	= 1,
77 };
78 
79 /*
80  * Put a cap on the size of the DRC based on the amount of available
81  * low memory in the machine.
82  *
83  *  64MB:    8192
84  * 128MB:   11585
85  * 256MB:   16384
86  * 512MB:   23170
87  *   1GB:   32768
88  *   2GB:   46340
89  *   4GB:   65536
90  *   8GB:   92681
91  *  16GB:  131072
92  *
93  * ...with a hard cap of 256k entries. In the worst case, each entry will be
94  * ~1k, so the above numbers should give a rough max of the amount of memory
95  * used in k.
96  */
97 static unsigned int
nfsd_cache_size_limit(void)98 nfsd_cache_size_limit(void)
99 {
100 	unsigned int limit;
101 	unsigned long low_pages = totalram_pages - totalhigh_pages;
102 
103 	limit = (16 * int_sqrt(low_pages)) << (PAGE_SHIFT-10);
104 	return min_t(unsigned int, limit, 256*1024);
105 }
106 
107 /*
108  * Compute the number of hash buckets we need. Divide the max cachesize by
109  * the "target" max bucket size, and round up to next power of two.
110  */
111 static unsigned int
nfsd_hashsize(unsigned int limit)112 nfsd_hashsize(unsigned int limit)
113 {
114 	return roundup_pow_of_two(limit / TARGET_BUCKET_SIZE);
115 }
116 
117 static u32
nfsd_cache_hash(__be32 xid)118 nfsd_cache_hash(__be32 xid)
119 {
120 	return hash_32(be32_to_cpu(xid), maskbits);
121 }
122 
123 static struct svc_cacherep *
nfsd_reply_cache_alloc(void)124 nfsd_reply_cache_alloc(void)
125 {
126 	struct svc_cacherep	*rp;
127 
128 	rp = kmem_cache_alloc(drc_slab, GFP_KERNEL);
129 	if (rp) {
130 		rp->c_state = RC_UNUSED;
131 		rp->c_type = RC_NOCACHE;
132 		INIT_LIST_HEAD(&rp->c_lru);
133 	}
134 	return rp;
135 }
136 
137 static void
nfsd_reply_cache_free_locked(struct svc_cacherep * rp)138 nfsd_reply_cache_free_locked(struct svc_cacherep *rp)
139 {
140 	if (rp->c_type == RC_REPLBUFF && rp->c_replvec.iov_base) {
141 		drc_mem_usage -= rp->c_replvec.iov_len;
142 		kfree(rp->c_replvec.iov_base);
143 	}
144 	list_del(&rp->c_lru);
145 	atomic_dec(&num_drc_entries);
146 	drc_mem_usage -= sizeof(*rp);
147 	kmem_cache_free(drc_slab, rp);
148 }
149 
150 static void
nfsd_reply_cache_free(struct nfsd_drc_bucket * b,struct svc_cacherep * rp)151 nfsd_reply_cache_free(struct nfsd_drc_bucket *b, struct svc_cacherep *rp)
152 {
153 	spin_lock(&b->cache_lock);
154 	nfsd_reply_cache_free_locked(rp);
155 	spin_unlock(&b->cache_lock);
156 }
157 
nfsd_reply_cache_init(void)158 int nfsd_reply_cache_init(void)
159 {
160 	unsigned int hashsize;
161 	unsigned int i;
162 	int status = 0;
163 
164 	max_drc_entries = nfsd_cache_size_limit();
165 	atomic_set(&num_drc_entries, 0);
166 	hashsize = nfsd_hashsize(max_drc_entries);
167 	maskbits = ilog2(hashsize);
168 
169 	status = register_shrinker(&nfsd_reply_cache_shrinker);
170 	if (status)
171 		return status;
172 
173 	drc_slab = kmem_cache_create("nfsd_drc", sizeof(struct svc_cacherep),
174 					0, 0, NULL);
175 	if (!drc_slab)
176 		goto out_nomem;
177 
178 	drc_hashtbl = kcalloc(hashsize, sizeof(*drc_hashtbl), GFP_KERNEL);
179 	if (!drc_hashtbl) {
180 		drc_hashtbl = vzalloc(array_size(hashsize,
181 						 sizeof(*drc_hashtbl)));
182 		if (!drc_hashtbl)
183 			goto out_nomem;
184 	}
185 
186 	for (i = 0; i < hashsize; i++) {
187 		INIT_LIST_HEAD(&drc_hashtbl[i].lru_head);
188 		spin_lock_init(&drc_hashtbl[i].cache_lock);
189 	}
190 	drc_hashsize = hashsize;
191 
192 	return 0;
193 out_nomem:
194 	printk(KERN_ERR "nfsd: failed to allocate reply cache\n");
195 	nfsd_reply_cache_shutdown();
196 	return -ENOMEM;
197 }
198 
nfsd_reply_cache_shutdown(void)199 void nfsd_reply_cache_shutdown(void)
200 {
201 	struct svc_cacherep	*rp;
202 	unsigned int i;
203 
204 	unregister_shrinker(&nfsd_reply_cache_shrinker);
205 
206 	for (i = 0; i < drc_hashsize; i++) {
207 		struct list_head *head = &drc_hashtbl[i].lru_head;
208 		while (!list_empty(head)) {
209 			rp = list_first_entry(head, struct svc_cacherep, c_lru);
210 			nfsd_reply_cache_free_locked(rp);
211 		}
212 	}
213 
214 	kvfree(drc_hashtbl);
215 	drc_hashtbl = NULL;
216 	drc_hashsize = 0;
217 
218 	kmem_cache_destroy(drc_slab);
219 	drc_slab = NULL;
220 }
221 
222 /*
223  * Move cache entry to end of LRU list, and queue the cleaner to run if it's
224  * not already scheduled.
225  */
226 static void
lru_put_end(struct nfsd_drc_bucket * b,struct svc_cacherep * rp)227 lru_put_end(struct nfsd_drc_bucket *b, struct svc_cacherep *rp)
228 {
229 	rp->c_timestamp = jiffies;
230 	list_move_tail(&rp->c_lru, &b->lru_head);
231 }
232 
233 static long
prune_bucket(struct nfsd_drc_bucket * b)234 prune_bucket(struct nfsd_drc_bucket *b)
235 {
236 	struct svc_cacherep *rp, *tmp;
237 	long freed = 0;
238 
239 	list_for_each_entry_safe(rp, tmp, &b->lru_head, c_lru) {
240 		/*
241 		 * Don't free entries attached to calls that are still
242 		 * in-progress, but do keep scanning the list.
243 		 */
244 		if (rp->c_state == RC_INPROG)
245 			continue;
246 		if (atomic_read(&num_drc_entries) <= max_drc_entries &&
247 		    time_before(jiffies, rp->c_timestamp + RC_EXPIRE))
248 			break;
249 		nfsd_reply_cache_free_locked(rp);
250 		freed++;
251 	}
252 	return freed;
253 }
254 
255 /*
256  * Walk the LRU list and prune off entries that are older than RC_EXPIRE.
257  * Also prune the oldest ones when the total exceeds the max number of entries.
258  */
259 static long
prune_cache_entries(void)260 prune_cache_entries(void)
261 {
262 	unsigned int i;
263 	long freed = 0;
264 
265 	for (i = 0; i < drc_hashsize; i++) {
266 		struct nfsd_drc_bucket *b = &drc_hashtbl[i];
267 
268 		if (list_empty(&b->lru_head))
269 			continue;
270 		spin_lock(&b->cache_lock);
271 		freed += prune_bucket(b);
272 		spin_unlock(&b->cache_lock);
273 	}
274 	return freed;
275 }
276 
277 static unsigned long
nfsd_reply_cache_count(struct shrinker * shrink,struct shrink_control * sc)278 nfsd_reply_cache_count(struct shrinker *shrink, struct shrink_control *sc)
279 {
280 	return atomic_read(&num_drc_entries);
281 }
282 
283 static unsigned long
nfsd_reply_cache_scan(struct shrinker * shrink,struct shrink_control * sc)284 nfsd_reply_cache_scan(struct shrinker *shrink, struct shrink_control *sc)
285 {
286 	return prune_cache_entries();
287 }
288 /*
289  * Walk an xdr_buf and get a CRC for at most the first RC_CSUMLEN bytes
290  */
291 static __wsum
nfsd_cache_csum(struct svc_rqst * rqstp)292 nfsd_cache_csum(struct svc_rqst *rqstp)
293 {
294 	int idx;
295 	unsigned int base;
296 	__wsum csum;
297 	struct xdr_buf *buf = &rqstp->rq_arg;
298 	const unsigned char *p = buf->head[0].iov_base;
299 	size_t csum_len = min_t(size_t, buf->head[0].iov_len + buf->page_len,
300 				RC_CSUMLEN);
301 	size_t len = min(buf->head[0].iov_len, csum_len);
302 
303 	/* rq_arg.head first */
304 	csum = csum_partial(p, len, 0);
305 	csum_len -= len;
306 
307 	/* Continue into page array */
308 	idx = buf->page_base / PAGE_SIZE;
309 	base = buf->page_base & ~PAGE_MASK;
310 	while (csum_len) {
311 		p = page_address(buf->pages[idx]) + base;
312 		len = min_t(size_t, PAGE_SIZE - base, csum_len);
313 		csum = csum_partial(p, len, csum);
314 		csum_len -= len;
315 		base = 0;
316 		++idx;
317 	}
318 	return csum;
319 }
320 
321 static bool
nfsd_cache_match(struct svc_rqst * rqstp,__wsum csum,struct svc_cacherep * rp)322 nfsd_cache_match(struct svc_rqst *rqstp, __wsum csum, struct svc_cacherep *rp)
323 {
324 	/* Check RPC XID first */
325 	if (rqstp->rq_xid != rp->c_xid)
326 		return false;
327 	/* compare checksum of NFS data */
328 	if (csum != rp->c_csum) {
329 		++payload_misses;
330 		return false;
331 	}
332 
333 	/* Other discriminators */
334 	if (rqstp->rq_proc != rp->c_proc ||
335 	    rqstp->rq_prot != rp->c_prot ||
336 	    rqstp->rq_vers != rp->c_vers ||
337 	    rqstp->rq_arg.len != rp->c_len ||
338 	    !rpc_cmp_addr(svc_addr(rqstp), (struct sockaddr *)&rp->c_addr) ||
339 	    rpc_get_port(svc_addr(rqstp)) != rpc_get_port((struct sockaddr *)&rp->c_addr))
340 		return false;
341 
342 	return true;
343 }
344 
345 /*
346  * Search the request hash for an entry that matches the given rqstp.
347  * Must be called with cache_lock held. Returns the found entry or
348  * NULL on failure.
349  */
350 static struct svc_cacherep *
nfsd_cache_search(struct nfsd_drc_bucket * b,struct svc_rqst * rqstp,__wsum csum)351 nfsd_cache_search(struct nfsd_drc_bucket *b, struct svc_rqst *rqstp,
352 		__wsum csum)
353 {
354 	struct svc_cacherep	*rp, *ret = NULL;
355 	struct list_head 	*rh = &b->lru_head;
356 	unsigned int		entries = 0;
357 
358 	list_for_each_entry(rp, rh, c_lru) {
359 		++entries;
360 		if (nfsd_cache_match(rqstp, csum, rp)) {
361 			ret = rp;
362 			break;
363 		}
364 	}
365 
366 	/* tally hash chain length stats */
367 	if (entries > longest_chain) {
368 		longest_chain = entries;
369 		longest_chain_cachesize = atomic_read(&num_drc_entries);
370 	} else if (entries == longest_chain) {
371 		/* prefer to keep the smallest cachesize possible here */
372 		longest_chain_cachesize = min_t(unsigned int,
373 				longest_chain_cachesize,
374 				atomic_read(&num_drc_entries));
375 	}
376 
377 	return ret;
378 }
379 
380 /*
381  * Try to find an entry matching the current call in the cache. When none
382  * is found, we try to grab the oldest expired entry off the LRU list. If
383  * a suitable one isn't there, then drop the cache_lock and allocate a
384  * new one, then search again in case one got inserted while this thread
385  * didn't hold the lock.
386  */
387 int
nfsd_cache_lookup(struct svc_rqst * rqstp)388 nfsd_cache_lookup(struct svc_rqst *rqstp)
389 {
390 	struct svc_cacherep	*rp, *found;
391 	__be32			xid = rqstp->rq_xid;
392 	u32			proto =  rqstp->rq_prot,
393 				vers = rqstp->rq_vers,
394 				proc = rqstp->rq_proc;
395 	__wsum			csum;
396 	u32 hash = nfsd_cache_hash(xid);
397 	struct nfsd_drc_bucket *b = &drc_hashtbl[hash];
398 	int type = rqstp->rq_cachetype;
399 	int rtn = RC_DOIT;
400 
401 	rqstp->rq_cacherep = NULL;
402 	if (type == RC_NOCACHE) {
403 		nfsdstats.rcnocache++;
404 		return rtn;
405 	}
406 
407 	csum = nfsd_cache_csum(rqstp);
408 
409 	/*
410 	 * Since the common case is a cache miss followed by an insert,
411 	 * preallocate an entry.
412 	 */
413 	rp = nfsd_reply_cache_alloc();
414 	spin_lock(&b->cache_lock);
415 	if (likely(rp)) {
416 		atomic_inc(&num_drc_entries);
417 		drc_mem_usage += sizeof(*rp);
418 	}
419 
420 	/* go ahead and prune the cache */
421 	prune_bucket(b);
422 
423 	found = nfsd_cache_search(b, rqstp, csum);
424 	if (found) {
425 		if (likely(rp))
426 			nfsd_reply_cache_free_locked(rp);
427 		rp = found;
428 		goto found_entry;
429 	}
430 
431 	if (!rp) {
432 		dprintk("nfsd: unable to allocate DRC entry!\n");
433 		goto out;
434 	}
435 
436 	nfsdstats.rcmisses++;
437 	rqstp->rq_cacherep = rp;
438 	rp->c_state = RC_INPROG;
439 	rp->c_xid = xid;
440 	rp->c_proc = proc;
441 	rpc_copy_addr((struct sockaddr *)&rp->c_addr, svc_addr(rqstp));
442 	rpc_set_port((struct sockaddr *)&rp->c_addr, rpc_get_port(svc_addr(rqstp)));
443 	rp->c_prot = proto;
444 	rp->c_vers = vers;
445 	rp->c_len = rqstp->rq_arg.len;
446 	rp->c_csum = csum;
447 
448 	lru_put_end(b, rp);
449 
450 	/* release any buffer */
451 	if (rp->c_type == RC_REPLBUFF) {
452 		drc_mem_usage -= rp->c_replvec.iov_len;
453 		kfree(rp->c_replvec.iov_base);
454 		rp->c_replvec.iov_base = NULL;
455 	}
456 	rp->c_type = RC_NOCACHE;
457  out:
458 	spin_unlock(&b->cache_lock);
459 	return rtn;
460 
461 found_entry:
462 	nfsdstats.rchits++;
463 	/* We found a matching entry which is either in progress or done. */
464 	lru_put_end(b, rp);
465 
466 	rtn = RC_DROPIT;
467 	/* Request being processed */
468 	if (rp->c_state == RC_INPROG)
469 		goto out;
470 
471 	/* From the hall of fame of impractical attacks:
472 	 * Is this a user who tries to snoop on the cache? */
473 	rtn = RC_DOIT;
474 	if (!test_bit(RQ_SECURE, &rqstp->rq_flags) && rp->c_secure)
475 		goto out;
476 
477 	/* Compose RPC reply header */
478 	switch (rp->c_type) {
479 	case RC_NOCACHE:
480 		break;
481 	case RC_REPLSTAT:
482 		svc_putu32(&rqstp->rq_res.head[0], rp->c_replstat);
483 		rtn = RC_REPLY;
484 		break;
485 	case RC_REPLBUFF:
486 		if (!nfsd_cache_append(rqstp, &rp->c_replvec))
487 			goto out;	/* should not happen */
488 		rtn = RC_REPLY;
489 		break;
490 	default:
491 		printk(KERN_WARNING "nfsd: bad repcache type %d\n", rp->c_type);
492 		nfsd_reply_cache_free_locked(rp);
493 	}
494 
495 	goto out;
496 }
497 
498 /*
499  * Update a cache entry. This is called from nfsd_dispatch when
500  * the procedure has been executed and the complete reply is in
501  * rqstp->rq_res.
502  *
503  * We're copying around data here rather than swapping buffers because
504  * the toplevel loop requires max-sized buffers, which would be a waste
505  * of memory for a cache with a max reply size of 100 bytes (diropokres).
506  *
507  * If we should start to use different types of cache entries tailored
508  * specifically for attrstat and fh's, we may save even more space.
509  *
510  * Also note that a cachetype of RC_NOCACHE can legally be passed when
511  * nfsd failed to encode a reply that otherwise would have been cached.
512  * In this case, nfsd_cache_update is called with statp == NULL.
513  */
514 void
nfsd_cache_update(struct svc_rqst * rqstp,int cachetype,__be32 * statp)515 nfsd_cache_update(struct svc_rqst *rqstp, int cachetype, __be32 *statp)
516 {
517 	struct svc_cacherep *rp = rqstp->rq_cacherep;
518 	struct kvec	*resv = &rqstp->rq_res.head[0], *cachv;
519 	u32		hash;
520 	struct nfsd_drc_bucket *b;
521 	int		len;
522 	size_t		bufsize = 0;
523 
524 	if (!rp)
525 		return;
526 
527 	hash = nfsd_cache_hash(rp->c_xid);
528 	b = &drc_hashtbl[hash];
529 
530 	len = resv->iov_len - ((char*)statp - (char*)resv->iov_base);
531 	len >>= 2;
532 
533 	/* Don't cache excessive amounts of data and XDR failures */
534 	if (!statp || len > (256 >> 2)) {
535 		nfsd_reply_cache_free(b, rp);
536 		return;
537 	}
538 
539 	switch (cachetype) {
540 	case RC_REPLSTAT:
541 		if (len != 1)
542 			printk("nfsd: RC_REPLSTAT/reply len %d!\n",len);
543 		rp->c_replstat = *statp;
544 		break;
545 	case RC_REPLBUFF:
546 		cachv = &rp->c_replvec;
547 		bufsize = len << 2;
548 		cachv->iov_base = kmalloc(bufsize, GFP_KERNEL);
549 		if (!cachv->iov_base) {
550 			nfsd_reply_cache_free(b, rp);
551 			return;
552 		}
553 		cachv->iov_len = bufsize;
554 		memcpy(cachv->iov_base, statp, bufsize);
555 		break;
556 	case RC_NOCACHE:
557 		nfsd_reply_cache_free(b, rp);
558 		return;
559 	}
560 	spin_lock(&b->cache_lock);
561 	drc_mem_usage += bufsize;
562 	lru_put_end(b, rp);
563 	rp->c_secure = test_bit(RQ_SECURE, &rqstp->rq_flags);
564 	rp->c_type = cachetype;
565 	rp->c_state = RC_DONE;
566 	spin_unlock(&b->cache_lock);
567 	return;
568 }
569 
570 /*
571  * Copy cached reply to current reply buffer. Should always fit.
572  * FIXME as reply is in a page, we should just attach the page, and
573  * keep a refcount....
574  */
575 static int
nfsd_cache_append(struct svc_rqst * rqstp,struct kvec * data)576 nfsd_cache_append(struct svc_rqst *rqstp, struct kvec *data)
577 {
578 	struct kvec	*vec = &rqstp->rq_res.head[0];
579 
580 	if (vec->iov_len + data->iov_len > PAGE_SIZE) {
581 		printk(KERN_WARNING "nfsd: cached reply too large (%zd).\n",
582 				data->iov_len);
583 		return 0;
584 	}
585 	memcpy((char*)vec->iov_base + vec->iov_len, data->iov_base, data->iov_len);
586 	vec->iov_len += data->iov_len;
587 	return 1;
588 }
589 
590 /*
591  * Note that fields may be added, removed or reordered in the future. Programs
592  * scraping this file for info should test the labels to ensure they're
593  * getting the correct field.
594  */
nfsd_reply_cache_stats_show(struct seq_file * m,void * v)595 static int nfsd_reply_cache_stats_show(struct seq_file *m, void *v)
596 {
597 	seq_printf(m, "max entries:           %u\n", max_drc_entries);
598 	seq_printf(m, "num entries:           %u\n",
599 			atomic_read(&num_drc_entries));
600 	seq_printf(m, "hash buckets:          %u\n", 1 << maskbits);
601 	seq_printf(m, "mem usage:             %u\n", drc_mem_usage);
602 	seq_printf(m, "cache hits:            %u\n", nfsdstats.rchits);
603 	seq_printf(m, "cache misses:          %u\n", nfsdstats.rcmisses);
604 	seq_printf(m, "not cached:            %u\n", nfsdstats.rcnocache);
605 	seq_printf(m, "payload misses:        %u\n", payload_misses);
606 	seq_printf(m, "longest chain len:     %u\n", longest_chain);
607 	seq_printf(m, "cachesize at longest:  %u\n", longest_chain_cachesize);
608 	return 0;
609 }
610 
nfsd_reply_cache_stats_open(struct inode * inode,struct file * file)611 int nfsd_reply_cache_stats_open(struct inode *inode, struct file *file)
612 {
613 	return single_open(file, nfsd_reply_cache_stats_show, NULL);
614 }
615