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1 // SPDX-License-Identifier: GPL-2.0-only
2 /*
3  * Memory merging support.
4  *
5  * This code enables dynamic sharing of identical pages found in different
6  * memory areas, even if they are not shared by fork()
7  *
8  * Copyright (C) 2008-2009 Red Hat, Inc.
9  * Authors:
10  *	Izik Eidus
11  *	Andrea Arcangeli
12  *	Chris Wright
13  *	Hugh Dickins
14  */
15 
16 #include <linux/errno.h>
17 #include <linux/mm.h>
18 #include <linux/fs.h>
19 #include <linux/mman.h>
20 #include <linux/sched.h>
21 #include <linux/sched/mm.h>
22 #include <linux/sched/coredump.h>
23 #include <linux/rwsem.h>
24 #include <linux/pagemap.h>
25 #include <linux/rmap.h>
26 #include <linux/spinlock.h>
27 #include <linux/xxhash.h>
28 #include <linux/delay.h>
29 #include <linux/kthread.h>
30 #include <linux/wait.h>
31 #include <linux/slab.h>
32 #include <linux/rbtree.h>
33 #include <linux/memory.h>
34 #include <linux/mmu_notifier.h>
35 #include <linux/swap.h>
36 #include <linux/ksm.h>
37 #include <linux/hashtable.h>
38 #include <linux/freezer.h>
39 #include <linux/oom.h>
40 #include <linux/numa.h>
41 
42 #include <asm/tlbflush.h>
43 #include "internal.h"
44 
45 #ifdef CONFIG_NUMA
46 #define NUMA(x)		(x)
47 #define DO_NUMA(x)	do { (x); } while (0)
48 #else
49 #define NUMA(x)		(0)
50 #define DO_NUMA(x)	do { } while (0)
51 #endif
52 
53 /**
54  * DOC: Overview
55  *
56  * A few notes about the KSM scanning process,
57  * to make it easier to understand the data structures below:
58  *
59  * In order to reduce excessive scanning, KSM sorts the memory pages by their
60  * contents into a data structure that holds pointers to the pages' locations.
61  *
62  * Since the contents of the pages may change at any moment, KSM cannot just
63  * insert the pages into a normal sorted tree and expect it to find anything.
64  * Therefore KSM uses two data structures - the stable and the unstable tree.
65  *
66  * The stable tree holds pointers to all the merged pages (ksm pages), sorted
67  * by their contents.  Because each such page is write-protected, searching on
68  * this tree is fully assured to be working (except when pages are unmapped),
69  * and therefore this tree is called the stable tree.
70  *
71  * The stable tree node includes information required for reverse
72  * mapping from a KSM page to virtual addresses that map this page.
73  *
74  * In order to avoid large latencies of the rmap walks on KSM pages,
75  * KSM maintains two types of nodes in the stable tree:
76  *
77  * * the regular nodes that keep the reverse mapping structures in a
78  *   linked list
79  * * the "chains" that link nodes ("dups") that represent the same
80  *   write protected memory content, but each "dup" corresponds to a
81  *   different KSM page copy of that content
82  *
83  * Internally, the regular nodes, "dups" and "chains" are represented
84  * using the same struct stable_node structure.
85  *
86  * In addition to the stable tree, KSM uses a second data structure called the
87  * unstable tree: this tree holds pointers to pages which have been found to
88  * be "unchanged for a period of time".  The unstable tree sorts these pages
89  * by their contents, but since they are not write-protected, KSM cannot rely
90  * upon the unstable tree to work correctly - the unstable tree is liable to
91  * be corrupted as its contents are modified, and so it is called unstable.
92  *
93  * KSM solves this problem by several techniques:
94  *
95  * 1) The unstable tree is flushed every time KSM completes scanning all
96  *    memory areas, and then the tree is rebuilt again from the beginning.
97  * 2) KSM will only insert into the unstable tree, pages whose hash value
98  *    has not changed since the previous scan of all memory areas.
99  * 3) The unstable tree is a RedBlack Tree - so its balancing is based on the
100  *    colors of the nodes and not on their contents, assuring that even when
101  *    the tree gets "corrupted" it won't get out of balance, so scanning time
102  *    remains the same (also, searching and inserting nodes in an rbtree uses
103  *    the same algorithm, so we have no overhead when we flush and rebuild).
104  * 4) KSM never flushes the stable tree, which means that even if it were to
105  *    take 10 attempts to find a page in the unstable tree, once it is found,
106  *    it is secured in the stable tree.  (When we scan a new page, we first
107  *    compare it against the stable tree, and then against the unstable tree.)
108  *
109  * If the merge_across_nodes tunable is unset, then KSM maintains multiple
110  * stable trees and multiple unstable trees: one of each for each NUMA node.
111  */
112 
113 /**
114  * struct mm_slot - ksm information per mm that is being scanned
115  * @link: link to the mm_slots hash list
116  * @mm_list: link into the mm_slots list, rooted in ksm_mm_head
117  * @rmap_list: head for this mm_slot's singly-linked list of rmap_items
118  * @mm: the mm that this information is valid for
119  */
120 struct mm_slot {
121 	struct hlist_node link;
122 	struct list_head mm_list;
123 	struct rmap_item *rmap_list;
124 	struct mm_struct *mm;
125 };
126 
127 /**
128  * struct ksm_scan - cursor for scanning
129  * @mm_slot: the current mm_slot we are scanning
130  * @address: the next address inside that to be scanned
131  * @rmap_list: link to the next rmap to be scanned in the rmap_list
132  * @seqnr: count of completed full scans (needed when removing unstable node)
133  *
134  * There is only the one ksm_scan instance of this cursor structure.
135  */
136 struct ksm_scan {
137 	struct mm_slot *mm_slot;
138 	unsigned long address;
139 	struct rmap_item **rmap_list;
140 	unsigned long seqnr;
141 };
142 
143 /**
144  * struct stable_node - node of the stable rbtree
145  * @node: rb node of this ksm page in the stable tree
146  * @head: (overlaying parent) &migrate_nodes indicates temporarily on that list
147  * @hlist_dup: linked into the stable_node->hlist with a stable_node chain
148  * @list: linked into migrate_nodes, pending placement in the proper node tree
149  * @hlist: hlist head of rmap_items using this ksm page
150  * @kpfn: page frame number of this ksm page (perhaps temporarily on wrong nid)
151  * @chain_prune_time: time of the last full garbage collection
152  * @rmap_hlist_len: number of rmap_item entries in hlist or STABLE_NODE_CHAIN
153  * @nid: NUMA node id of stable tree in which linked (may not match kpfn)
154  */
155 struct stable_node {
156 	union {
157 		struct rb_node node;	/* when node of stable tree */
158 		struct {		/* when listed for migration */
159 			struct list_head *head;
160 			struct {
161 				struct hlist_node hlist_dup;
162 				struct list_head list;
163 			};
164 		};
165 	};
166 	struct hlist_head hlist;
167 	union {
168 		unsigned long kpfn;
169 		unsigned long chain_prune_time;
170 	};
171 	/*
172 	 * STABLE_NODE_CHAIN can be any negative number in
173 	 * rmap_hlist_len negative range, but better not -1 to be able
174 	 * to reliably detect underflows.
175 	 */
176 #define STABLE_NODE_CHAIN -1024
177 	int rmap_hlist_len;
178 #ifdef CONFIG_NUMA
179 	int nid;
180 #endif
181 };
182 
183 /**
184  * struct rmap_item - reverse mapping item for virtual addresses
185  * @rmap_list: next rmap_item in mm_slot's singly-linked rmap_list
186  * @anon_vma: pointer to anon_vma for this mm,address, when in stable tree
187  * @nid: NUMA node id of unstable tree in which linked (may not match page)
188  * @mm: the memory structure this rmap_item is pointing into
189  * @address: the virtual address this rmap_item tracks (+ flags in low bits)
190  * @oldchecksum: previous checksum of the page at that virtual address
191  * @node: rb node of this rmap_item in the unstable tree
192  * @head: pointer to stable_node heading this list in the stable tree
193  * @hlist: link into hlist of rmap_items hanging off that stable_node
194  */
195 struct rmap_item {
196 	struct rmap_item *rmap_list;
197 	union {
198 		struct anon_vma *anon_vma;	/* when stable */
199 #ifdef CONFIG_NUMA
200 		int nid;		/* when node of unstable tree */
201 #endif
202 	};
203 	struct mm_struct *mm;
204 	unsigned long address;		/* + low bits used for flags below */
205 	unsigned int oldchecksum;	/* when unstable */
206 	union {
207 		struct rb_node node;	/* when node of unstable tree */
208 		struct {		/* when listed from stable tree */
209 			struct stable_node *head;
210 			struct hlist_node hlist;
211 		};
212 	};
213 };
214 
215 #define SEQNR_MASK	0x0ff	/* low bits of unstable tree seqnr */
216 #define UNSTABLE_FLAG	0x100	/* is a node of the unstable tree */
217 #define STABLE_FLAG	0x200	/* is listed from the stable tree */
218 
219 /* The stable and unstable tree heads */
220 static struct rb_root one_stable_tree[1] = { RB_ROOT };
221 static struct rb_root one_unstable_tree[1] = { RB_ROOT };
222 static struct rb_root *root_stable_tree = one_stable_tree;
223 static struct rb_root *root_unstable_tree = one_unstable_tree;
224 
225 /* Recently migrated nodes of stable tree, pending proper placement */
226 static LIST_HEAD(migrate_nodes);
227 #define STABLE_NODE_DUP_HEAD ((struct list_head *)&migrate_nodes.prev)
228 
229 #define MM_SLOTS_HASH_BITS 10
230 static DEFINE_HASHTABLE(mm_slots_hash, MM_SLOTS_HASH_BITS);
231 
232 static struct mm_slot ksm_mm_head = {
233 	.mm_list = LIST_HEAD_INIT(ksm_mm_head.mm_list),
234 };
235 static struct ksm_scan ksm_scan = {
236 	.mm_slot = &ksm_mm_head,
237 };
238 
239 static struct kmem_cache *rmap_item_cache;
240 static struct kmem_cache *stable_node_cache;
241 static struct kmem_cache *mm_slot_cache;
242 
243 /* The number of nodes in the stable tree */
244 static unsigned long ksm_pages_shared;
245 
246 /* The number of page slots additionally sharing those nodes */
247 static unsigned long ksm_pages_sharing;
248 
249 /* The number of nodes in the unstable tree */
250 static unsigned long ksm_pages_unshared;
251 
252 /* The number of rmap_items in use: to calculate pages_volatile */
253 static unsigned long ksm_rmap_items;
254 
255 /* The number of stable_node chains */
256 static unsigned long ksm_stable_node_chains;
257 
258 /* The number of stable_node dups linked to the stable_node chains */
259 static unsigned long ksm_stable_node_dups;
260 
261 /* Delay in pruning stale stable_node_dups in the stable_node_chains */
262 static unsigned int ksm_stable_node_chains_prune_millisecs = 2000;
263 
264 /* Maximum number of page slots sharing a stable node */
265 static int ksm_max_page_sharing = 256;
266 
267 /* Number of pages ksmd should scan in one batch */
268 static unsigned int ksm_thread_pages_to_scan = 100;
269 
270 /* Milliseconds ksmd should sleep between batches */
271 static unsigned int ksm_thread_sleep_millisecs = 20;
272 
273 /* Checksum of an empty (zeroed) page */
274 static unsigned int zero_checksum __read_mostly;
275 
276 /* Whether to merge empty (zeroed) pages with actual zero pages */
277 static bool ksm_use_zero_pages __read_mostly;
278 
279 #ifdef CONFIG_NUMA
280 /* Zeroed when merging across nodes is not allowed */
281 static unsigned int ksm_merge_across_nodes = 1;
282 static int ksm_nr_node_ids = 1;
283 #else
284 #define ksm_merge_across_nodes	1U
285 #define ksm_nr_node_ids		1
286 #endif
287 
288 #define KSM_RUN_STOP	0
289 #define KSM_RUN_MERGE	1
290 #define KSM_RUN_UNMERGE	2
291 #define KSM_RUN_OFFLINE	4
292 static unsigned long ksm_run = KSM_RUN_STOP;
293 static void wait_while_offlining(void);
294 
295 static DECLARE_WAIT_QUEUE_HEAD(ksm_thread_wait);
296 static DECLARE_WAIT_QUEUE_HEAD(ksm_iter_wait);
297 static DEFINE_MUTEX(ksm_thread_mutex);
298 static DEFINE_SPINLOCK(ksm_mmlist_lock);
299 
300 #define KSM_KMEM_CACHE(__struct, __flags) kmem_cache_create("ksm_"#__struct,\
301 		sizeof(struct __struct), __alignof__(struct __struct),\
302 		(__flags), NULL)
303 
ksm_slab_init(void)304 static int __init ksm_slab_init(void)
305 {
306 	rmap_item_cache = KSM_KMEM_CACHE(rmap_item, 0);
307 	if (!rmap_item_cache)
308 		goto out;
309 
310 	stable_node_cache = KSM_KMEM_CACHE(stable_node, 0);
311 	if (!stable_node_cache)
312 		goto out_free1;
313 
314 	mm_slot_cache = KSM_KMEM_CACHE(mm_slot, 0);
315 	if (!mm_slot_cache)
316 		goto out_free2;
317 
318 	return 0;
319 
320 out_free2:
321 	kmem_cache_destroy(stable_node_cache);
322 out_free1:
323 	kmem_cache_destroy(rmap_item_cache);
324 out:
325 	return -ENOMEM;
326 }
327 
ksm_slab_free(void)328 static void __init ksm_slab_free(void)
329 {
330 	kmem_cache_destroy(mm_slot_cache);
331 	kmem_cache_destroy(stable_node_cache);
332 	kmem_cache_destroy(rmap_item_cache);
333 	mm_slot_cache = NULL;
334 }
335 
is_stable_node_chain(struct stable_node * chain)336 static __always_inline bool is_stable_node_chain(struct stable_node *chain)
337 {
338 	return chain->rmap_hlist_len == STABLE_NODE_CHAIN;
339 }
340 
is_stable_node_dup(struct stable_node * dup)341 static __always_inline bool is_stable_node_dup(struct stable_node *dup)
342 {
343 	return dup->head == STABLE_NODE_DUP_HEAD;
344 }
345 
stable_node_chain_add_dup(struct stable_node * dup,struct stable_node * chain)346 static inline void stable_node_chain_add_dup(struct stable_node *dup,
347 					     struct stable_node *chain)
348 {
349 	VM_BUG_ON(is_stable_node_dup(dup));
350 	dup->head = STABLE_NODE_DUP_HEAD;
351 	VM_BUG_ON(!is_stable_node_chain(chain));
352 	hlist_add_head(&dup->hlist_dup, &chain->hlist);
353 	ksm_stable_node_dups++;
354 }
355 
__stable_node_dup_del(struct stable_node * dup)356 static inline void __stable_node_dup_del(struct stable_node *dup)
357 {
358 	VM_BUG_ON(!is_stable_node_dup(dup));
359 	hlist_del(&dup->hlist_dup);
360 	ksm_stable_node_dups--;
361 }
362 
stable_node_dup_del(struct stable_node * dup)363 static inline void stable_node_dup_del(struct stable_node *dup)
364 {
365 	VM_BUG_ON(is_stable_node_chain(dup));
366 	if (is_stable_node_dup(dup))
367 		__stable_node_dup_del(dup);
368 	else
369 		rb_erase(&dup->node, root_stable_tree + NUMA(dup->nid));
370 #ifdef CONFIG_DEBUG_VM
371 	dup->head = NULL;
372 #endif
373 }
374 
alloc_rmap_item(void)375 static inline struct rmap_item *alloc_rmap_item(void)
376 {
377 	struct rmap_item *rmap_item;
378 
379 	rmap_item = kmem_cache_zalloc(rmap_item_cache, GFP_KERNEL |
380 						__GFP_NORETRY | __GFP_NOWARN);
381 	if (rmap_item)
382 		ksm_rmap_items++;
383 	return rmap_item;
384 }
385 
free_rmap_item(struct rmap_item * rmap_item)386 static inline void free_rmap_item(struct rmap_item *rmap_item)
387 {
388 	ksm_rmap_items--;
389 	rmap_item->mm = NULL;	/* debug safety */
390 	kmem_cache_free(rmap_item_cache, rmap_item);
391 }
392 
alloc_stable_node(void)393 static inline struct stable_node *alloc_stable_node(void)
394 {
395 	/*
396 	 * The allocation can take too long with GFP_KERNEL when memory is under
397 	 * pressure, which may lead to hung task warnings.  Adding __GFP_HIGH
398 	 * grants access to memory reserves, helping to avoid this problem.
399 	 */
400 	return kmem_cache_alloc(stable_node_cache, GFP_KERNEL | __GFP_HIGH);
401 }
402 
free_stable_node(struct stable_node * stable_node)403 static inline void free_stable_node(struct stable_node *stable_node)
404 {
405 	VM_BUG_ON(stable_node->rmap_hlist_len &&
406 		  !is_stable_node_chain(stable_node));
407 	kmem_cache_free(stable_node_cache, stable_node);
408 }
409 
alloc_mm_slot(void)410 static inline struct mm_slot *alloc_mm_slot(void)
411 {
412 	if (!mm_slot_cache)	/* initialization failed */
413 		return NULL;
414 	return kmem_cache_zalloc(mm_slot_cache, GFP_KERNEL);
415 }
416 
free_mm_slot(struct mm_slot * mm_slot)417 static inline void free_mm_slot(struct mm_slot *mm_slot)
418 {
419 	kmem_cache_free(mm_slot_cache, mm_slot);
420 }
421 
get_mm_slot(struct mm_struct * mm)422 static struct mm_slot *get_mm_slot(struct mm_struct *mm)
423 {
424 	struct mm_slot *slot;
425 
426 	hash_for_each_possible(mm_slots_hash, slot, link, (unsigned long)mm)
427 		if (slot->mm == mm)
428 			return slot;
429 
430 	return NULL;
431 }
432 
insert_to_mm_slots_hash(struct mm_struct * mm,struct mm_slot * mm_slot)433 static void insert_to_mm_slots_hash(struct mm_struct *mm,
434 				    struct mm_slot *mm_slot)
435 {
436 	mm_slot->mm = mm;
437 	hash_add(mm_slots_hash, &mm_slot->link, (unsigned long)mm);
438 }
439 
440 /*
441  * ksmd, and unmerge_and_remove_all_rmap_items(), must not touch an mm's
442  * page tables after it has passed through ksm_exit() - which, if necessary,
443  * takes mmap_lock briefly to serialize against them.  ksm_exit() does not set
444  * a special flag: they can just back out as soon as mm_users goes to zero.
445  * ksm_test_exit() is used throughout to make this test for exit: in some
446  * places for correctness, in some places just to avoid unnecessary work.
447  */
ksm_test_exit(struct mm_struct * mm)448 static inline bool ksm_test_exit(struct mm_struct *mm)
449 {
450 	return atomic_read(&mm->mm_users) == 0;
451 }
452 
453 /*
454  * We use break_ksm to break COW on a ksm page: it's a stripped down
455  *
456  *	if (get_user_pages(addr, 1, FOLL_WRITE, &page, NULL) == 1)
457  *		put_page(page);
458  *
459  * but taking great care only to touch a ksm page, in a VM_MERGEABLE vma,
460  * in case the application has unmapped and remapped mm,addr meanwhile.
461  * Could a ksm page appear anywhere else?  Actually yes, in a VM_PFNMAP
462  * mmap of /dev/mem, where we would not want to touch it.
463  *
464  * FAULT_FLAG/FOLL_REMOTE are because we do this outside the context
465  * of the process that owns 'vma'.  We also do not want to enforce
466  * protection keys here anyway.
467  */
break_ksm(struct vm_area_struct * vma,unsigned long addr)468 static int break_ksm(struct vm_area_struct *vma, unsigned long addr)
469 {
470 	struct page *page;
471 	vm_fault_t ret = 0;
472 
473 	do {
474 		cond_resched();
475 		page = follow_page(vma, addr,
476 				FOLL_GET | FOLL_MIGRATION | FOLL_REMOTE);
477 		if (IS_ERR_OR_NULL(page))
478 			break;
479 		if (PageKsm(page))
480 			ret = handle_mm_fault(vma, addr,
481 					      FAULT_FLAG_WRITE | FAULT_FLAG_REMOTE,
482 					      NULL);
483 		else
484 			ret = VM_FAULT_WRITE;
485 		put_page(page);
486 	} while (!(ret & (VM_FAULT_WRITE | VM_FAULT_SIGBUS | VM_FAULT_SIGSEGV | VM_FAULT_OOM)));
487 	/*
488 	 * We must loop because handle_mm_fault() may back out if there's
489 	 * any difficulty e.g. if pte accessed bit gets updated concurrently.
490 	 *
491 	 * VM_FAULT_WRITE is what we have been hoping for: it indicates that
492 	 * COW has been broken, even if the vma does not permit VM_WRITE;
493 	 * but note that a concurrent fault might break PageKsm for us.
494 	 *
495 	 * VM_FAULT_SIGBUS could occur if we race with truncation of the
496 	 * backing file, which also invalidates anonymous pages: that's
497 	 * okay, that truncation will have unmapped the PageKsm for us.
498 	 *
499 	 * VM_FAULT_OOM: at the time of writing (late July 2009), setting
500 	 * aside mem_cgroup limits, VM_FAULT_OOM would only be set if the
501 	 * current task has TIF_MEMDIE set, and will be OOM killed on return
502 	 * to user; and ksmd, having no mm, would never be chosen for that.
503 	 *
504 	 * But if the mm is in a limited mem_cgroup, then the fault may fail
505 	 * with VM_FAULT_OOM even if the current task is not TIF_MEMDIE; and
506 	 * even ksmd can fail in this way - though it's usually breaking ksm
507 	 * just to undo a merge it made a moment before, so unlikely to oom.
508 	 *
509 	 * That's a pity: we might therefore have more kernel pages allocated
510 	 * than we're counting as nodes in the stable tree; but ksm_do_scan
511 	 * will retry to break_cow on each pass, so should recover the page
512 	 * in due course.  The important thing is to not let VM_MERGEABLE
513 	 * be cleared while any such pages might remain in the area.
514 	 */
515 	return (ret & VM_FAULT_OOM) ? -ENOMEM : 0;
516 }
517 
find_mergeable_vma(struct mm_struct * mm,unsigned long addr)518 static struct vm_area_struct *find_mergeable_vma(struct mm_struct *mm,
519 		unsigned long addr)
520 {
521 	struct vm_area_struct *vma;
522 	if (ksm_test_exit(mm))
523 		return NULL;
524 	vma = vma_lookup(mm, addr);
525 	if (!vma || !(vma->vm_flags & VM_MERGEABLE) || !vma->anon_vma)
526 		return NULL;
527 	return vma;
528 }
529 
break_cow(struct rmap_item * rmap_item)530 static void break_cow(struct rmap_item *rmap_item)
531 {
532 	struct mm_struct *mm = rmap_item->mm;
533 	unsigned long addr = rmap_item->address;
534 	struct vm_area_struct *vma;
535 
536 	/*
537 	 * It is not an accident that whenever we want to break COW
538 	 * to undo, we also need to drop a reference to the anon_vma.
539 	 */
540 	put_anon_vma(rmap_item->anon_vma);
541 
542 	mmap_read_lock(mm);
543 	vma = find_mergeable_vma(mm, addr);
544 	if (vma)
545 		break_ksm(vma, addr);
546 	mmap_read_unlock(mm);
547 }
548 
get_mergeable_page(struct rmap_item * rmap_item)549 static struct page *get_mergeable_page(struct rmap_item *rmap_item)
550 {
551 	struct mm_struct *mm = rmap_item->mm;
552 	unsigned long addr = rmap_item->address;
553 	struct vm_area_struct *vma;
554 	struct page *page;
555 
556 	mmap_read_lock(mm);
557 	vma = find_mergeable_vma(mm, addr);
558 	if (!vma)
559 		goto out;
560 
561 	page = follow_page(vma, addr, FOLL_GET);
562 	if (IS_ERR_OR_NULL(page))
563 		goto out;
564 	if (PageAnon(page)) {
565 		flush_anon_page(vma, page, addr);
566 		flush_dcache_page(page);
567 	} else {
568 		put_page(page);
569 out:
570 		page = NULL;
571 	}
572 	mmap_read_unlock(mm);
573 	return page;
574 }
575 
576 /*
577  * This helper is used for getting right index into array of tree roots.
578  * When merge_across_nodes knob is set to 1, there are only two rb-trees for
579  * stable and unstable pages from all nodes with roots in index 0. Otherwise,
580  * every node has its own stable and unstable tree.
581  */
get_kpfn_nid(unsigned long kpfn)582 static inline int get_kpfn_nid(unsigned long kpfn)
583 {
584 	return ksm_merge_across_nodes ? 0 : NUMA(pfn_to_nid(kpfn));
585 }
586 
alloc_stable_node_chain(struct stable_node * dup,struct rb_root * root)587 static struct stable_node *alloc_stable_node_chain(struct stable_node *dup,
588 						   struct rb_root *root)
589 {
590 	struct stable_node *chain = alloc_stable_node();
591 	VM_BUG_ON(is_stable_node_chain(dup));
592 	if (likely(chain)) {
593 		INIT_HLIST_HEAD(&chain->hlist);
594 		chain->chain_prune_time = jiffies;
595 		chain->rmap_hlist_len = STABLE_NODE_CHAIN;
596 #if defined (CONFIG_DEBUG_VM) && defined(CONFIG_NUMA)
597 		chain->nid = NUMA_NO_NODE; /* debug */
598 #endif
599 		ksm_stable_node_chains++;
600 
601 		/*
602 		 * Put the stable node chain in the first dimension of
603 		 * the stable tree and at the same time remove the old
604 		 * stable node.
605 		 */
606 		rb_replace_node(&dup->node, &chain->node, root);
607 
608 		/*
609 		 * Move the old stable node to the second dimension
610 		 * queued in the hlist_dup. The invariant is that all
611 		 * dup stable_nodes in the chain->hlist point to pages
612 		 * that are write protected and have the exact same
613 		 * content.
614 		 */
615 		stable_node_chain_add_dup(dup, chain);
616 	}
617 	return chain;
618 }
619 
free_stable_node_chain(struct stable_node * chain,struct rb_root * root)620 static inline void free_stable_node_chain(struct stable_node *chain,
621 					  struct rb_root *root)
622 {
623 	rb_erase(&chain->node, root);
624 	free_stable_node(chain);
625 	ksm_stable_node_chains--;
626 }
627 
remove_node_from_stable_tree(struct stable_node * stable_node)628 static void remove_node_from_stable_tree(struct stable_node *stable_node)
629 {
630 	struct rmap_item *rmap_item;
631 
632 	/* check it's not STABLE_NODE_CHAIN or negative */
633 	BUG_ON(stable_node->rmap_hlist_len < 0);
634 
635 	hlist_for_each_entry(rmap_item, &stable_node->hlist, hlist) {
636 		if (rmap_item->hlist.next)
637 			ksm_pages_sharing--;
638 		else
639 			ksm_pages_shared--;
640 		VM_BUG_ON(stable_node->rmap_hlist_len <= 0);
641 		stable_node->rmap_hlist_len--;
642 		put_anon_vma(rmap_item->anon_vma);
643 		rmap_item->address &= PAGE_MASK;
644 		cond_resched();
645 	}
646 
647 	/*
648 	 * We need the second aligned pointer of the migrate_nodes
649 	 * list_head to stay clear from the rb_parent_color union
650 	 * (aligned and different than any node) and also different
651 	 * from &migrate_nodes. This will verify that future list.h changes
652 	 * don't break STABLE_NODE_DUP_HEAD. Only recent gcc can handle it.
653 	 */
654 	BUILD_BUG_ON(STABLE_NODE_DUP_HEAD <= &migrate_nodes);
655 	BUILD_BUG_ON(STABLE_NODE_DUP_HEAD >= &migrate_nodes + 1);
656 
657 	if (stable_node->head == &migrate_nodes)
658 		list_del(&stable_node->list);
659 	else
660 		stable_node_dup_del(stable_node);
661 	free_stable_node(stable_node);
662 }
663 
664 enum get_ksm_page_flags {
665 	GET_KSM_PAGE_NOLOCK,
666 	GET_KSM_PAGE_LOCK,
667 	GET_KSM_PAGE_TRYLOCK
668 };
669 
670 /*
671  * get_ksm_page: checks if the page indicated by the stable node
672  * is still its ksm page, despite having held no reference to it.
673  * In which case we can trust the content of the page, and it
674  * returns the gotten page; but if the page has now been zapped,
675  * remove the stale node from the stable tree and return NULL.
676  * But beware, the stable node's page might be being migrated.
677  *
678  * You would expect the stable_node to hold a reference to the ksm page.
679  * But if it increments the page's count, swapping out has to wait for
680  * ksmd to come around again before it can free the page, which may take
681  * seconds or even minutes: much too unresponsive.  So instead we use a
682  * "keyhole reference": access to the ksm page from the stable node peeps
683  * out through its keyhole to see if that page still holds the right key,
684  * pointing back to this stable node.  This relies on freeing a PageAnon
685  * page to reset its page->mapping to NULL, and relies on no other use of
686  * a page to put something that might look like our key in page->mapping.
687  * is on its way to being freed; but it is an anomaly to bear in mind.
688  */
get_ksm_page(struct stable_node * stable_node,enum get_ksm_page_flags flags)689 static struct page *get_ksm_page(struct stable_node *stable_node,
690 				 enum get_ksm_page_flags flags)
691 {
692 	struct page *page;
693 	void *expected_mapping;
694 	unsigned long kpfn;
695 
696 	expected_mapping = (void *)((unsigned long)stable_node |
697 					PAGE_MAPPING_KSM);
698 again:
699 	kpfn = READ_ONCE(stable_node->kpfn); /* Address dependency. */
700 	page = pfn_to_page(kpfn);
701 	if (READ_ONCE(page->mapping) != expected_mapping)
702 		goto stale;
703 
704 	/*
705 	 * We cannot do anything with the page while its refcount is 0.
706 	 * Usually 0 means free, or tail of a higher-order page: in which
707 	 * case this node is no longer referenced, and should be freed;
708 	 * however, it might mean that the page is under page_ref_freeze().
709 	 * The __remove_mapping() case is easy, again the node is now stale;
710 	 * the same is in reuse_ksm_page() case; but if page is swapcache
711 	 * in migrate_page_move_mapping(), it might still be our page,
712 	 * in which case it's essential to keep the node.
713 	 */
714 	while (!get_page_unless_zero(page)) {
715 		/*
716 		 * Another check for page->mapping != expected_mapping would
717 		 * work here too.  We have chosen the !PageSwapCache test to
718 		 * optimize the common case, when the page is or is about to
719 		 * be freed: PageSwapCache is cleared (under spin_lock_irq)
720 		 * in the ref_freeze section of __remove_mapping(); but Anon
721 		 * page->mapping reset to NULL later, in free_pages_prepare().
722 		 */
723 		if (!PageSwapCache(page))
724 			goto stale;
725 		cpu_relax();
726 	}
727 
728 	if (READ_ONCE(page->mapping) != expected_mapping) {
729 		put_page(page);
730 		goto stale;
731 	}
732 
733 	if (flags == GET_KSM_PAGE_TRYLOCK) {
734 		if (!trylock_page(page)) {
735 			put_page(page);
736 			return ERR_PTR(-EBUSY);
737 		}
738 	} else if (flags == GET_KSM_PAGE_LOCK)
739 		lock_page(page);
740 
741 	if (flags != GET_KSM_PAGE_NOLOCK) {
742 		if (READ_ONCE(page->mapping) != expected_mapping) {
743 			unlock_page(page);
744 			put_page(page);
745 			goto stale;
746 		}
747 	}
748 	return page;
749 
750 stale:
751 	/*
752 	 * We come here from above when page->mapping or !PageSwapCache
753 	 * suggests that the node is stale; but it might be under migration.
754 	 * We need smp_rmb(), matching the smp_wmb() in ksm_migrate_page(),
755 	 * before checking whether node->kpfn has been changed.
756 	 */
757 	smp_rmb();
758 	if (READ_ONCE(stable_node->kpfn) != kpfn)
759 		goto again;
760 	remove_node_from_stable_tree(stable_node);
761 	return NULL;
762 }
763 
764 /*
765  * Removing rmap_item from stable or unstable tree.
766  * This function will clean the information from the stable/unstable tree.
767  */
remove_rmap_item_from_tree(struct rmap_item * rmap_item)768 static void remove_rmap_item_from_tree(struct rmap_item *rmap_item)
769 {
770 	if (rmap_item->address & STABLE_FLAG) {
771 		struct stable_node *stable_node;
772 		struct page *page;
773 
774 		stable_node = rmap_item->head;
775 		page = get_ksm_page(stable_node, GET_KSM_PAGE_LOCK);
776 		if (!page)
777 			goto out;
778 
779 		hlist_del(&rmap_item->hlist);
780 		unlock_page(page);
781 		put_page(page);
782 
783 		if (!hlist_empty(&stable_node->hlist))
784 			ksm_pages_sharing--;
785 		else
786 			ksm_pages_shared--;
787 		VM_BUG_ON(stable_node->rmap_hlist_len <= 0);
788 		stable_node->rmap_hlist_len--;
789 
790 		put_anon_vma(rmap_item->anon_vma);
791 		rmap_item->head = NULL;
792 		rmap_item->address &= PAGE_MASK;
793 
794 	} else if (rmap_item->address & UNSTABLE_FLAG) {
795 		unsigned char age;
796 		/*
797 		 * Usually ksmd can and must skip the rb_erase, because
798 		 * root_unstable_tree was already reset to RB_ROOT.
799 		 * But be careful when an mm is exiting: do the rb_erase
800 		 * if this rmap_item was inserted by this scan, rather
801 		 * than left over from before.
802 		 */
803 		age = (unsigned char)(ksm_scan.seqnr - rmap_item->address);
804 		BUG_ON(age > 1);
805 		if (!age)
806 			rb_erase(&rmap_item->node,
807 				 root_unstable_tree + NUMA(rmap_item->nid));
808 		ksm_pages_unshared--;
809 		rmap_item->address &= PAGE_MASK;
810 	}
811 out:
812 	cond_resched();		/* we're called from many long loops */
813 }
814 
remove_trailing_rmap_items(struct rmap_item ** rmap_list)815 static void remove_trailing_rmap_items(struct rmap_item **rmap_list)
816 {
817 	while (*rmap_list) {
818 		struct rmap_item *rmap_item = *rmap_list;
819 		*rmap_list = rmap_item->rmap_list;
820 		remove_rmap_item_from_tree(rmap_item);
821 		free_rmap_item(rmap_item);
822 	}
823 }
824 
825 /*
826  * Though it's very tempting to unmerge rmap_items from stable tree rather
827  * than check every pte of a given vma, the locking doesn't quite work for
828  * that - an rmap_item is assigned to the stable tree after inserting ksm
829  * page and upping mmap_lock.  Nor does it fit with the way we skip dup'ing
830  * rmap_items from parent to child at fork time (so as not to waste time
831  * if exit comes before the next scan reaches it).
832  *
833  * Similarly, although we'd like to remove rmap_items (so updating counts
834  * and freeing memory) when unmerging an area, it's easier to leave that
835  * to the next pass of ksmd - consider, for example, how ksmd might be
836  * in cmp_and_merge_page on one of the rmap_items we would be removing.
837  */
unmerge_ksm_pages(struct vm_area_struct * vma,unsigned long start,unsigned long end)838 static int unmerge_ksm_pages(struct vm_area_struct *vma,
839 			     unsigned long start, unsigned long end)
840 {
841 	unsigned long addr;
842 	int err = 0;
843 
844 	for (addr = start; addr < end && !err; addr += PAGE_SIZE) {
845 		if (ksm_test_exit(vma->vm_mm))
846 			break;
847 		if (signal_pending(current))
848 			err = -ERESTARTSYS;
849 		else
850 			err = break_ksm(vma, addr);
851 	}
852 	return err;
853 }
854 
page_stable_node(struct page * page)855 static inline struct stable_node *page_stable_node(struct page *page)
856 {
857 	return PageKsm(page) ? page_rmapping(page) : NULL;
858 }
859 
set_page_stable_node(struct page * page,struct stable_node * stable_node)860 static inline void set_page_stable_node(struct page *page,
861 					struct stable_node *stable_node)
862 {
863 	page->mapping = (void *)((unsigned long)stable_node | PAGE_MAPPING_KSM);
864 }
865 
866 #ifdef CONFIG_SYSFS
867 /*
868  * Only called through the sysfs control interface:
869  */
remove_stable_node(struct stable_node * stable_node)870 static int remove_stable_node(struct stable_node *stable_node)
871 {
872 	struct page *page;
873 	int err;
874 
875 	page = get_ksm_page(stable_node, GET_KSM_PAGE_LOCK);
876 	if (!page) {
877 		/*
878 		 * get_ksm_page did remove_node_from_stable_tree itself.
879 		 */
880 		return 0;
881 	}
882 
883 	/*
884 	 * Page could be still mapped if this races with __mmput() running in
885 	 * between ksm_exit() and exit_mmap(). Just refuse to let
886 	 * merge_across_nodes/max_page_sharing be switched.
887 	 */
888 	err = -EBUSY;
889 	if (!page_mapped(page)) {
890 		/*
891 		 * The stable node did not yet appear stale to get_ksm_page(),
892 		 * since that allows for an unmapped ksm page to be recognized
893 		 * right up until it is freed; but the node is safe to remove.
894 		 * This page might be in a pagevec waiting to be freed,
895 		 * or it might be PageSwapCache (perhaps under writeback),
896 		 * or it might have been removed from swapcache a moment ago.
897 		 */
898 		set_page_stable_node(page, NULL);
899 		remove_node_from_stable_tree(stable_node);
900 		err = 0;
901 	}
902 
903 	unlock_page(page);
904 	put_page(page);
905 	return err;
906 }
907 
remove_stable_node_chain(struct stable_node * stable_node,struct rb_root * root)908 static int remove_stable_node_chain(struct stable_node *stable_node,
909 				    struct rb_root *root)
910 {
911 	struct stable_node *dup;
912 	struct hlist_node *hlist_safe;
913 
914 	if (!is_stable_node_chain(stable_node)) {
915 		VM_BUG_ON(is_stable_node_dup(stable_node));
916 		if (remove_stable_node(stable_node))
917 			return true;
918 		else
919 			return false;
920 	}
921 
922 	hlist_for_each_entry_safe(dup, hlist_safe,
923 				  &stable_node->hlist, hlist_dup) {
924 		VM_BUG_ON(!is_stable_node_dup(dup));
925 		if (remove_stable_node(dup))
926 			return true;
927 	}
928 	BUG_ON(!hlist_empty(&stable_node->hlist));
929 	free_stable_node_chain(stable_node, root);
930 	return false;
931 }
932 
remove_all_stable_nodes(void)933 static int remove_all_stable_nodes(void)
934 {
935 	struct stable_node *stable_node, *next;
936 	int nid;
937 	int err = 0;
938 
939 	for (nid = 0; nid < ksm_nr_node_ids; nid++) {
940 		while (root_stable_tree[nid].rb_node) {
941 			stable_node = rb_entry(root_stable_tree[nid].rb_node,
942 						struct stable_node, node);
943 			if (remove_stable_node_chain(stable_node,
944 						     root_stable_tree + nid)) {
945 				err = -EBUSY;
946 				break;	/* proceed to next nid */
947 			}
948 			cond_resched();
949 		}
950 	}
951 	list_for_each_entry_safe(stable_node, next, &migrate_nodes, list) {
952 		if (remove_stable_node(stable_node))
953 			err = -EBUSY;
954 		cond_resched();
955 	}
956 	return err;
957 }
958 
unmerge_and_remove_all_rmap_items(void)959 static int unmerge_and_remove_all_rmap_items(void)
960 {
961 	struct mm_slot *mm_slot;
962 	struct mm_struct *mm;
963 	struct vm_area_struct *vma;
964 	int err = 0;
965 
966 	spin_lock(&ksm_mmlist_lock);
967 	ksm_scan.mm_slot = list_entry(ksm_mm_head.mm_list.next,
968 						struct mm_slot, mm_list);
969 	spin_unlock(&ksm_mmlist_lock);
970 
971 	for (mm_slot = ksm_scan.mm_slot;
972 			mm_slot != &ksm_mm_head; mm_slot = ksm_scan.mm_slot) {
973 		mm = mm_slot->mm;
974 		mmap_read_lock(mm);
975 		for (vma = mm->mmap; vma; vma = vma->vm_next) {
976 			if (ksm_test_exit(mm))
977 				break;
978 			if (!(vma->vm_flags & VM_MERGEABLE) || !vma->anon_vma)
979 				continue;
980 			err = unmerge_ksm_pages(vma,
981 						vma->vm_start, vma->vm_end);
982 			if (err)
983 				goto error;
984 		}
985 
986 		remove_trailing_rmap_items(&mm_slot->rmap_list);
987 		mmap_read_unlock(mm);
988 
989 		spin_lock(&ksm_mmlist_lock);
990 		ksm_scan.mm_slot = list_entry(mm_slot->mm_list.next,
991 						struct mm_slot, mm_list);
992 		if (ksm_test_exit(mm)) {
993 			hash_del(&mm_slot->link);
994 			list_del(&mm_slot->mm_list);
995 			spin_unlock(&ksm_mmlist_lock);
996 
997 			free_mm_slot(mm_slot);
998 			clear_bit(MMF_VM_MERGEABLE, &mm->flags);
999 			mmdrop(mm);
1000 		} else
1001 			spin_unlock(&ksm_mmlist_lock);
1002 	}
1003 
1004 	/* Clean up stable nodes, but don't worry if some are still busy */
1005 	remove_all_stable_nodes();
1006 	ksm_scan.seqnr = 0;
1007 	return 0;
1008 
1009 error:
1010 	mmap_read_unlock(mm);
1011 	spin_lock(&ksm_mmlist_lock);
1012 	ksm_scan.mm_slot = &ksm_mm_head;
1013 	spin_unlock(&ksm_mmlist_lock);
1014 	return err;
1015 }
1016 #endif /* CONFIG_SYSFS */
1017 
calc_checksum(struct page * page)1018 static u32 calc_checksum(struct page *page)
1019 {
1020 	u32 checksum;
1021 	void *addr = kmap_atomic(page);
1022 	checksum = xxhash(addr, PAGE_SIZE, 0);
1023 	kunmap_atomic(addr);
1024 	return checksum;
1025 }
1026 
write_protect_page(struct vm_area_struct * vma,struct page * page,pte_t * orig_pte)1027 static int write_protect_page(struct vm_area_struct *vma, struct page *page,
1028 			      pte_t *orig_pte)
1029 {
1030 	struct mm_struct *mm = vma->vm_mm;
1031 	struct page_vma_mapped_walk pvmw = {
1032 		.page = page,
1033 		.vma = vma,
1034 	};
1035 	int swapped;
1036 	int err = -EFAULT;
1037 	struct mmu_notifier_range range;
1038 
1039 	pvmw.address = page_address_in_vma(page, vma);
1040 	if (pvmw.address == -EFAULT)
1041 		goto out;
1042 
1043 	BUG_ON(PageTransCompound(page));
1044 
1045 	mmu_notifier_range_init(&range, MMU_NOTIFY_CLEAR, 0, vma, mm,
1046 				pvmw.address,
1047 				pvmw.address + PAGE_SIZE);
1048 	mmu_notifier_invalidate_range_start(&range);
1049 
1050 	if (!page_vma_mapped_walk(&pvmw))
1051 		goto out_mn;
1052 	if (WARN_ONCE(!pvmw.pte, "Unexpected PMD mapping?"))
1053 		goto out_unlock;
1054 
1055 	if (pte_write(*pvmw.pte) || pte_dirty(*pvmw.pte) ||
1056 	    (pte_protnone(*pvmw.pte) && pte_savedwrite(*pvmw.pte)) ||
1057 						mm_tlb_flush_pending(mm)) {
1058 		pte_t entry;
1059 
1060 		swapped = PageSwapCache(page);
1061 		flush_cache_page(vma, pvmw.address, page_to_pfn(page));
1062 		/*
1063 		 * Ok this is tricky, when get_user_pages_fast() run it doesn't
1064 		 * take any lock, therefore the check that we are going to make
1065 		 * with the pagecount against the mapcount is racy and
1066 		 * O_DIRECT can happen right after the check.
1067 		 * So we clear the pte and flush the tlb before the check
1068 		 * this assure us that no O_DIRECT can happen after the check
1069 		 * or in the middle of the check.
1070 		 *
1071 		 * No need to notify as we are downgrading page table to read
1072 		 * only not changing it to point to a new page.
1073 		 *
1074 		 * See Documentation/vm/mmu_notifier.rst
1075 		 */
1076 		entry = ptep_clear_flush(vma, pvmw.address, pvmw.pte);
1077 		/*
1078 		 * Check that no O_DIRECT or similar I/O is in progress on the
1079 		 * page
1080 		 */
1081 		if (page_mapcount(page) + 1 + swapped != page_count(page)) {
1082 			set_pte_at(mm, pvmw.address, pvmw.pte, entry);
1083 			goto out_unlock;
1084 		}
1085 		if (pte_dirty(entry))
1086 			set_page_dirty(page);
1087 
1088 		if (pte_protnone(entry))
1089 			entry = pte_mkclean(pte_clear_savedwrite(entry));
1090 		else
1091 			entry = pte_mkclean(pte_wrprotect(entry));
1092 		set_pte_at_notify(mm, pvmw.address, pvmw.pte, entry);
1093 	}
1094 	*orig_pte = *pvmw.pte;
1095 	err = 0;
1096 
1097 out_unlock:
1098 	page_vma_mapped_walk_done(&pvmw);
1099 out_mn:
1100 	mmu_notifier_invalidate_range_end(&range);
1101 out:
1102 	return err;
1103 }
1104 
1105 /**
1106  * replace_page - replace page in vma by new ksm page
1107  * @vma:      vma that holds the pte pointing to page
1108  * @page:     the page we are replacing by kpage
1109  * @kpage:    the ksm page we replace page by
1110  * @orig_pte: the original value of the pte
1111  *
1112  * Returns 0 on success, -EFAULT on failure.
1113  */
replace_page(struct vm_area_struct * vma,struct page * page,struct page * kpage,pte_t orig_pte)1114 static int replace_page(struct vm_area_struct *vma, struct page *page,
1115 			struct page *kpage, pte_t orig_pte)
1116 {
1117 	struct mm_struct *mm = vma->vm_mm;
1118 	pmd_t *pmd;
1119 	pte_t *ptep;
1120 	pte_t newpte;
1121 	spinlock_t *ptl;
1122 	unsigned long addr;
1123 	int err = -EFAULT;
1124 	struct mmu_notifier_range range;
1125 
1126 	addr = page_address_in_vma(page, vma);
1127 	if (addr == -EFAULT)
1128 		goto out;
1129 
1130 	pmd = mm_find_pmd(mm, addr);
1131 	if (!pmd)
1132 		goto out;
1133 
1134 	mmu_notifier_range_init(&range, MMU_NOTIFY_CLEAR, 0, vma, mm, addr,
1135 				addr + PAGE_SIZE);
1136 	mmu_notifier_invalidate_range_start(&range);
1137 
1138 	ptep = pte_offset_map_lock(mm, pmd, addr, &ptl);
1139 	if (!pte_same(*ptep, orig_pte)) {
1140 		pte_unmap_unlock(ptep, ptl);
1141 		goto out_mn;
1142 	}
1143 
1144 	/*
1145 	 * No need to check ksm_use_zero_pages here: we can only have a
1146 	 * zero_page here if ksm_use_zero_pages was enabled already.
1147 	 */
1148 	if (!is_zero_pfn(page_to_pfn(kpage))) {
1149 		get_page(kpage);
1150 		page_add_anon_rmap(kpage, vma, addr, false);
1151 		newpte = mk_pte(kpage, vma->vm_page_prot);
1152 	} else {
1153 		newpte = pte_mkspecial(pfn_pte(page_to_pfn(kpage),
1154 					       vma->vm_page_prot));
1155 		/*
1156 		 * We're replacing an anonymous page with a zero page, which is
1157 		 * not anonymous. We need to do proper accounting otherwise we
1158 		 * will get wrong values in /proc, and a BUG message in dmesg
1159 		 * when tearing down the mm.
1160 		 */
1161 		dec_mm_counter(mm, MM_ANONPAGES);
1162 	}
1163 
1164 	flush_cache_page(vma, addr, pte_pfn(*ptep));
1165 	/*
1166 	 * No need to notify as we are replacing a read only page with another
1167 	 * read only page with the same content.
1168 	 *
1169 	 * See Documentation/vm/mmu_notifier.rst
1170 	 */
1171 	ptep_clear_flush(vma, addr, ptep);
1172 	set_pte_at_notify(mm, addr, ptep, newpte);
1173 
1174 	page_remove_rmap(page, false);
1175 	if (!page_mapped(page))
1176 		try_to_free_swap(page);
1177 	put_page(page);
1178 
1179 	pte_unmap_unlock(ptep, ptl);
1180 	err = 0;
1181 out_mn:
1182 	mmu_notifier_invalidate_range_end(&range);
1183 out:
1184 	return err;
1185 }
1186 
1187 /*
1188  * try_to_merge_one_page - take two pages and merge them into one
1189  * @vma: the vma that holds the pte pointing to page
1190  * @page: the PageAnon page that we want to replace with kpage
1191  * @kpage: the PageKsm page that we want to map instead of page,
1192  *         or NULL the first time when we want to use page as kpage.
1193  *
1194  * This function returns 0 if the pages were merged, -EFAULT otherwise.
1195  */
try_to_merge_one_page(struct vm_area_struct * vma,struct page * page,struct page * kpage)1196 static int try_to_merge_one_page(struct vm_area_struct *vma,
1197 				 struct page *page, struct page *kpage)
1198 {
1199 	pte_t orig_pte = __pte(0);
1200 	int err = -EFAULT;
1201 
1202 	if (page == kpage)			/* ksm page forked */
1203 		return 0;
1204 
1205 	if (!PageAnon(page))
1206 		goto out;
1207 
1208 	/*
1209 	 * We need the page lock to read a stable PageSwapCache in
1210 	 * write_protect_page().  We use trylock_page() instead of
1211 	 * lock_page() because we don't want to wait here - we
1212 	 * prefer to continue scanning and merging different pages,
1213 	 * then come back to this page when it is unlocked.
1214 	 */
1215 	if (!trylock_page(page))
1216 		goto out;
1217 
1218 	if (PageTransCompound(page)) {
1219 		if (split_huge_page(page))
1220 			goto out_unlock;
1221 	}
1222 
1223 	/*
1224 	 * If this anonymous page is mapped only here, its pte may need
1225 	 * to be write-protected.  If it's mapped elsewhere, all of its
1226 	 * ptes are necessarily already write-protected.  But in either
1227 	 * case, we need to lock and check page_count is not raised.
1228 	 */
1229 	if (write_protect_page(vma, page, &orig_pte) == 0) {
1230 		if (!kpage) {
1231 			/*
1232 			 * While we hold page lock, upgrade page from
1233 			 * PageAnon+anon_vma to PageKsm+NULL stable_node:
1234 			 * stable_tree_insert() will update stable_node.
1235 			 */
1236 			set_page_stable_node(page, NULL);
1237 			mark_page_accessed(page);
1238 			/*
1239 			 * Page reclaim just frees a clean page with no dirty
1240 			 * ptes: make sure that the ksm page would be swapped.
1241 			 */
1242 			if (!PageDirty(page))
1243 				SetPageDirty(page);
1244 			err = 0;
1245 		} else if (pages_identical(page, kpage))
1246 			err = replace_page(vma, page, kpage, orig_pte);
1247 	}
1248 
1249 	if ((vma->vm_flags & VM_LOCKED) && kpage && !err) {
1250 		munlock_vma_page(page);
1251 		if (!PageMlocked(kpage)) {
1252 			unlock_page(page);
1253 			lock_page(kpage);
1254 			mlock_vma_page(kpage);
1255 			page = kpage;		/* for final unlock */
1256 		}
1257 	}
1258 
1259 out_unlock:
1260 	unlock_page(page);
1261 out:
1262 	return err;
1263 }
1264 
1265 /*
1266  * try_to_merge_with_ksm_page - like try_to_merge_two_pages,
1267  * but no new kernel page is allocated: kpage must already be a ksm page.
1268  *
1269  * This function returns 0 if the pages were merged, -EFAULT otherwise.
1270  */
try_to_merge_with_ksm_page(struct rmap_item * rmap_item,struct page * page,struct page * kpage)1271 static int try_to_merge_with_ksm_page(struct rmap_item *rmap_item,
1272 				      struct page *page, struct page *kpage)
1273 {
1274 	struct mm_struct *mm = rmap_item->mm;
1275 	struct vm_area_struct *vma;
1276 	int err = -EFAULT;
1277 
1278 	mmap_read_lock(mm);
1279 	vma = find_mergeable_vma(mm, rmap_item->address);
1280 	if (!vma)
1281 		goto out;
1282 
1283 	err = try_to_merge_one_page(vma, page, kpage);
1284 	if (err)
1285 		goto out;
1286 
1287 	/* Unstable nid is in union with stable anon_vma: remove first */
1288 	remove_rmap_item_from_tree(rmap_item);
1289 
1290 	/* Must get reference to anon_vma while still holding mmap_lock */
1291 	rmap_item->anon_vma = vma->anon_vma;
1292 	get_anon_vma(vma->anon_vma);
1293 out:
1294 	mmap_read_unlock(mm);
1295 	return err;
1296 }
1297 
1298 /*
1299  * try_to_merge_two_pages - take two identical pages and prepare them
1300  * to be merged into one page.
1301  *
1302  * This function returns the kpage if we successfully merged two identical
1303  * pages into one ksm page, NULL otherwise.
1304  *
1305  * Note that this function upgrades page to ksm page: if one of the pages
1306  * is already a ksm page, try_to_merge_with_ksm_page should be used.
1307  */
try_to_merge_two_pages(struct rmap_item * rmap_item,struct page * page,struct rmap_item * tree_rmap_item,struct page * tree_page)1308 static struct page *try_to_merge_two_pages(struct rmap_item *rmap_item,
1309 					   struct page *page,
1310 					   struct rmap_item *tree_rmap_item,
1311 					   struct page *tree_page)
1312 {
1313 	int err;
1314 
1315 	err = try_to_merge_with_ksm_page(rmap_item, page, NULL);
1316 	if (!err) {
1317 		err = try_to_merge_with_ksm_page(tree_rmap_item,
1318 							tree_page, page);
1319 		/*
1320 		 * If that fails, we have a ksm page with only one pte
1321 		 * pointing to it: so break it.
1322 		 */
1323 		if (err)
1324 			break_cow(rmap_item);
1325 	}
1326 	return err ? NULL : page;
1327 }
1328 
1329 static __always_inline
__is_page_sharing_candidate(struct stable_node * stable_node,int offset)1330 bool __is_page_sharing_candidate(struct stable_node *stable_node, int offset)
1331 {
1332 	VM_BUG_ON(stable_node->rmap_hlist_len < 0);
1333 	/*
1334 	 * Check that at least one mapping still exists, otherwise
1335 	 * there's no much point to merge and share with this
1336 	 * stable_node, as the underlying tree_page of the other
1337 	 * sharer is going to be freed soon.
1338 	 */
1339 	return stable_node->rmap_hlist_len &&
1340 		stable_node->rmap_hlist_len + offset < ksm_max_page_sharing;
1341 }
1342 
1343 static __always_inline
is_page_sharing_candidate(struct stable_node * stable_node)1344 bool is_page_sharing_candidate(struct stable_node *stable_node)
1345 {
1346 	return __is_page_sharing_candidate(stable_node, 0);
1347 }
1348 
stable_node_dup(struct stable_node ** _stable_node_dup,struct stable_node ** _stable_node,struct rb_root * root,bool prune_stale_stable_nodes)1349 static struct page *stable_node_dup(struct stable_node **_stable_node_dup,
1350 				    struct stable_node **_stable_node,
1351 				    struct rb_root *root,
1352 				    bool prune_stale_stable_nodes)
1353 {
1354 	struct stable_node *dup, *found = NULL, *stable_node = *_stable_node;
1355 	struct hlist_node *hlist_safe;
1356 	struct page *_tree_page, *tree_page = NULL;
1357 	int nr = 0;
1358 	int found_rmap_hlist_len;
1359 
1360 	if (!prune_stale_stable_nodes ||
1361 	    time_before(jiffies, stable_node->chain_prune_time +
1362 			msecs_to_jiffies(
1363 				ksm_stable_node_chains_prune_millisecs)))
1364 		prune_stale_stable_nodes = false;
1365 	else
1366 		stable_node->chain_prune_time = jiffies;
1367 
1368 	hlist_for_each_entry_safe(dup, hlist_safe,
1369 				  &stable_node->hlist, hlist_dup) {
1370 		cond_resched();
1371 		/*
1372 		 * We must walk all stable_node_dup to prune the stale
1373 		 * stable nodes during lookup.
1374 		 *
1375 		 * get_ksm_page can drop the nodes from the
1376 		 * stable_node->hlist if they point to freed pages
1377 		 * (that's why we do a _safe walk). The "dup"
1378 		 * stable_node parameter itself will be freed from
1379 		 * under us if it returns NULL.
1380 		 */
1381 		_tree_page = get_ksm_page(dup, GET_KSM_PAGE_NOLOCK);
1382 		if (!_tree_page)
1383 			continue;
1384 		nr += 1;
1385 		if (is_page_sharing_candidate(dup)) {
1386 			if (!found ||
1387 			    dup->rmap_hlist_len > found_rmap_hlist_len) {
1388 				if (found)
1389 					put_page(tree_page);
1390 				found = dup;
1391 				found_rmap_hlist_len = found->rmap_hlist_len;
1392 				tree_page = _tree_page;
1393 
1394 				/* skip put_page for found dup */
1395 				if (!prune_stale_stable_nodes)
1396 					break;
1397 				continue;
1398 			}
1399 		}
1400 		put_page(_tree_page);
1401 	}
1402 
1403 	if (found) {
1404 		/*
1405 		 * nr is counting all dups in the chain only if
1406 		 * prune_stale_stable_nodes is true, otherwise we may
1407 		 * break the loop at nr == 1 even if there are
1408 		 * multiple entries.
1409 		 */
1410 		if (prune_stale_stable_nodes && nr == 1) {
1411 			/*
1412 			 * If there's not just one entry it would
1413 			 * corrupt memory, better BUG_ON. In KSM
1414 			 * context with no lock held it's not even
1415 			 * fatal.
1416 			 */
1417 			BUG_ON(stable_node->hlist.first->next);
1418 
1419 			/*
1420 			 * There's just one entry and it is below the
1421 			 * deduplication limit so drop the chain.
1422 			 */
1423 			rb_replace_node(&stable_node->node, &found->node,
1424 					root);
1425 			free_stable_node(stable_node);
1426 			ksm_stable_node_chains--;
1427 			ksm_stable_node_dups--;
1428 			/*
1429 			 * NOTE: the caller depends on the stable_node
1430 			 * to be equal to stable_node_dup if the chain
1431 			 * was collapsed.
1432 			 */
1433 			*_stable_node = found;
1434 			/*
1435 			 * Just for robustness, as stable_node is
1436 			 * otherwise left as a stable pointer, the
1437 			 * compiler shall optimize it away at build
1438 			 * time.
1439 			 */
1440 			stable_node = NULL;
1441 		} else if (stable_node->hlist.first != &found->hlist_dup &&
1442 			   __is_page_sharing_candidate(found, 1)) {
1443 			/*
1444 			 * If the found stable_node dup can accept one
1445 			 * more future merge (in addition to the one
1446 			 * that is underway) and is not at the head of
1447 			 * the chain, put it there so next search will
1448 			 * be quicker in the !prune_stale_stable_nodes
1449 			 * case.
1450 			 *
1451 			 * NOTE: it would be inaccurate to use nr > 1
1452 			 * instead of checking the hlist.first pointer
1453 			 * directly, because in the
1454 			 * prune_stale_stable_nodes case "nr" isn't
1455 			 * the position of the found dup in the chain,
1456 			 * but the total number of dups in the chain.
1457 			 */
1458 			hlist_del(&found->hlist_dup);
1459 			hlist_add_head(&found->hlist_dup,
1460 				       &stable_node->hlist);
1461 		}
1462 	}
1463 
1464 	*_stable_node_dup = found;
1465 	return tree_page;
1466 }
1467 
stable_node_dup_any(struct stable_node * stable_node,struct rb_root * root)1468 static struct stable_node *stable_node_dup_any(struct stable_node *stable_node,
1469 					       struct rb_root *root)
1470 {
1471 	if (!is_stable_node_chain(stable_node))
1472 		return stable_node;
1473 	if (hlist_empty(&stable_node->hlist)) {
1474 		free_stable_node_chain(stable_node, root);
1475 		return NULL;
1476 	}
1477 	return hlist_entry(stable_node->hlist.first,
1478 			   typeof(*stable_node), hlist_dup);
1479 }
1480 
1481 /*
1482  * Like for get_ksm_page, this function can free the *_stable_node and
1483  * *_stable_node_dup if the returned tree_page is NULL.
1484  *
1485  * It can also free and overwrite *_stable_node with the found
1486  * stable_node_dup if the chain is collapsed (in which case
1487  * *_stable_node will be equal to *_stable_node_dup like if the chain
1488  * never existed). It's up to the caller to verify tree_page is not
1489  * NULL before dereferencing *_stable_node or *_stable_node_dup.
1490  *
1491  * *_stable_node_dup is really a second output parameter of this
1492  * function and will be overwritten in all cases, the caller doesn't
1493  * need to initialize it.
1494  */
__stable_node_chain(struct stable_node ** _stable_node_dup,struct stable_node ** _stable_node,struct rb_root * root,bool prune_stale_stable_nodes)1495 static struct page *__stable_node_chain(struct stable_node **_stable_node_dup,
1496 					struct stable_node **_stable_node,
1497 					struct rb_root *root,
1498 					bool prune_stale_stable_nodes)
1499 {
1500 	struct stable_node *stable_node = *_stable_node;
1501 	if (!is_stable_node_chain(stable_node)) {
1502 		if (is_page_sharing_candidate(stable_node)) {
1503 			*_stable_node_dup = stable_node;
1504 			return get_ksm_page(stable_node, GET_KSM_PAGE_NOLOCK);
1505 		}
1506 		/*
1507 		 * _stable_node_dup set to NULL means the stable_node
1508 		 * reached the ksm_max_page_sharing limit.
1509 		 */
1510 		*_stable_node_dup = NULL;
1511 		return NULL;
1512 	}
1513 	return stable_node_dup(_stable_node_dup, _stable_node, root,
1514 			       prune_stale_stable_nodes);
1515 }
1516 
chain_prune(struct stable_node ** s_n_d,struct stable_node ** s_n,struct rb_root * root)1517 static __always_inline struct page *chain_prune(struct stable_node **s_n_d,
1518 						struct stable_node **s_n,
1519 						struct rb_root *root)
1520 {
1521 	return __stable_node_chain(s_n_d, s_n, root, true);
1522 }
1523 
chain(struct stable_node ** s_n_d,struct stable_node * s_n,struct rb_root * root)1524 static __always_inline struct page *chain(struct stable_node **s_n_d,
1525 					  struct stable_node *s_n,
1526 					  struct rb_root *root)
1527 {
1528 	struct stable_node *old_stable_node = s_n;
1529 	struct page *tree_page;
1530 
1531 	tree_page = __stable_node_chain(s_n_d, &s_n, root, false);
1532 	/* not pruning dups so s_n cannot have changed */
1533 	VM_BUG_ON(s_n != old_stable_node);
1534 	return tree_page;
1535 }
1536 
1537 /*
1538  * stable_tree_search - search for page inside the stable tree
1539  *
1540  * This function checks if there is a page inside the stable tree
1541  * with identical content to the page that we are scanning right now.
1542  *
1543  * This function returns the stable tree node of identical content if found,
1544  * NULL otherwise.
1545  */
stable_tree_search(struct page * page)1546 static struct page *stable_tree_search(struct page *page)
1547 {
1548 	int nid;
1549 	struct rb_root *root;
1550 	struct rb_node **new;
1551 	struct rb_node *parent;
1552 	struct stable_node *stable_node, *stable_node_dup, *stable_node_any;
1553 	struct stable_node *page_node;
1554 
1555 	page_node = page_stable_node(page);
1556 	if (page_node && page_node->head != &migrate_nodes) {
1557 		/* ksm page forked */
1558 		get_page(page);
1559 		return page;
1560 	}
1561 
1562 	nid = get_kpfn_nid(page_to_pfn(page));
1563 	root = root_stable_tree + nid;
1564 again:
1565 	new = &root->rb_node;
1566 	parent = NULL;
1567 
1568 	while (*new) {
1569 		struct page *tree_page;
1570 		int ret;
1571 
1572 		cond_resched();
1573 		stable_node = rb_entry(*new, struct stable_node, node);
1574 		stable_node_any = NULL;
1575 		tree_page = chain_prune(&stable_node_dup, &stable_node,	root);
1576 		/*
1577 		 * NOTE: stable_node may have been freed by
1578 		 * chain_prune() if the returned stable_node_dup is
1579 		 * not NULL. stable_node_dup may have been inserted in
1580 		 * the rbtree instead as a regular stable_node (in
1581 		 * order to collapse the stable_node chain if a single
1582 		 * stable_node dup was found in it). In such case the
1583 		 * stable_node is overwritten by the calleee to point
1584 		 * to the stable_node_dup that was collapsed in the
1585 		 * stable rbtree and stable_node will be equal to
1586 		 * stable_node_dup like if the chain never existed.
1587 		 */
1588 		if (!stable_node_dup) {
1589 			/*
1590 			 * Either all stable_node dups were full in
1591 			 * this stable_node chain, or this chain was
1592 			 * empty and should be rb_erased.
1593 			 */
1594 			stable_node_any = stable_node_dup_any(stable_node,
1595 							      root);
1596 			if (!stable_node_any) {
1597 				/* rb_erase just run */
1598 				goto again;
1599 			}
1600 			/*
1601 			 * Take any of the stable_node dups page of
1602 			 * this stable_node chain to let the tree walk
1603 			 * continue. All KSM pages belonging to the
1604 			 * stable_node dups in a stable_node chain
1605 			 * have the same content and they're
1606 			 * write protected at all times. Any will work
1607 			 * fine to continue the walk.
1608 			 */
1609 			tree_page = get_ksm_page(stable_node_any,
1610 						 GET_KSM_PAGE_NOLOCK);
1611 		}
1612 		VM_BUG_ON(!stable_node_dup ^ !!stable_node_any);
1613 		if (!tree_page) {
1614 			/*
1615 			 * If we walked over a stale stable_node,
1616 			 * get_ksm_page() will call rb_erase() and it
1617 			 * may rebalance the tree from under us. So
1618 			 * restart the search from scratch. Returning
1619 			 * NULL would be safe too, but we'd generate
1620 			 * false negative insertions just because some
1621 			 * stable_node was stale.
1622 			 */
1623 			goto again;
1624 		}
1625 
1626 		ret = memcmp_pages(page, tree_page);
1627 		put_page(tree_page);
1628 
1629 		parent = *new;
1630 		if (ret < 0)
1631 			new = &parent->rb_left;
1632 		else if (ret > 0)
1633 			new = &parent->rb_right;
1634 		else {
1635 			if (page_node) {
1636 				VM_BUG_ON(page_node->head != &migrate_nodes);
1637 				/*
1638 				 * Test if the migrated page should be merged
1639 				 * into a stable node dup. If the mapcount is
1640 				 * 1 we can migrate it with another KSM page
1641 				 * without adding it to the chain.
1642 				 */
1643 				if (page_mapcount(page) > 1)
1644 					goto chain_append;
1645 			}
1646 
1647 			if (!stable_node_dup) {
1648 				/*
1649 				 * If the stable_node is a chain and
1650 				 * we got a payload match in memcmp
1651 				 * but we cannot merge the scanned
1652 				 * page in any of the existing
1653 				 * stable_node dups because they're
1654 				 * all full, we need to wait the
1655 				 * scanned page to find itself a match
1656 				 * in the unstable tree to create a
1657 				 * brand new KSM page to add later to
1658 				 * the dups of this stable_node.
1659 				 */
1660 				return NULL;
1661 			}
1662 
1663 			/*
1664 			 * Lock and unlock the stable_node's page (which
1665 			 * might already have been migrated) so that page
1666 			 * migration is sure to notice its raised count.
1667 			 * It would be more elegant to return stable_node
1668 			 * than kpage, but that involves more changes.
1669 			 */
1670 			tree_page = get_ksm_page(stable_node_dup,
1671 						 GET_KSM_PAGE_TRYLOCK);
1672 
1673 			if (PTR_ERR(tree_page) == -EBUSY)
1674 				return ERR_PTR(-EBUSY);
1675 
1676 			if (unlikely(!tree_page))
1677 				/*
1678 				 * The tree may have been rebalanced,
1679 				 * so re-evaluate parent and new.
1680 				 */
1681 				goto again;
1682 			unlock_page(tree_page);
1683 
1684 			if (get_kpfn_nid(stable_node_dup->kpfn) !=
1685 			    NUMA(stable_node_dup->nid)) {
1686 				put_page(tree_page);
1687 				goto replace;
1688 			}
1689 			return tree_page;
1690 		}
1691 	}
1692 
1693 	if (!page_node)
1694 		return NULL;
1695 
1696 	list_del(&page_node->list);
1697 	DO_NUMA(page_node->nid = nid);
1698 	rb_link_node(&page_node->node, parent, new);
1699 	rb_insert_color(&page_node->node, root);
1700 out:
1701 	if (is_page_sharing_candidate(page_node)) {
1702 		get_page(page);
1703 		return page;
1704 	} else
1705 		return NULL;
1706 
1707 replace:
1708 	/*
1709 	 * If stable_node was a chain and chain_prune collapsed it,
1710 	 * stable_node has been updated to be the new regular
1711 	 * stable_node. A collapse of the chain is indistinguishable
1712 	 * from the case there was no chain in the stable
1713 	 * rbtree. Otherwise stable_node is the chain and
1714 	 * stable_node_dup is the dup to replace.
1715 	 */
1716 	if (stable_node_dup == stable_node) {
1717 		VM_BUG_ON(is_stable_node_chain(stable_node_dup));
1718 		VM_BUG_ON(is_stable_node_dup(stable_node_dup));
1719 		/* there is no chain */
1720 		if (page_node) {
1721 			VM_BUG_ON(page_node->head != &migrate_nodes);
1722 			list_del(&page_node->list);
1723 			DO_NUMA(page_node->nid = nid);
1724 			rb_replace_node(&stable_node_dup->node,
1725 					&page_node->node,
1726 					root);
1727 			if (is_page_sharing_candidate(page_node))
1728 				get_page(page);
1729 			else
1730 				page = NULL;
1731 		} else {
1732 			rb_erase(&stable_node_dup->node, root);
1733 			page = NULL;
1734 		}
1735 	} else {
1736 		VM_BUG_ON(!is_stable_node_chain(stable_node));
1737 		__stable_node_dup_del(stable_node_dup);
1738 		if (page_node) {
1739 			VM_BUG_ON(page_node->head != &migrate_nodes);
1740 			list_del(&page_node->list);
1741 			DO_NUMA(page_node->nid = nid);
1742 			stable_node_chain_add_dup(page_node, stable_node);
1743 			if (is_page_sharing_candidate(page_node))
1744 				get_page(page);
1745 			else
1746 				page = NULL;
1747 		} else {
1748 			page = NULL;
1749 		}
1750 	}
1751 	stable_node_dup->head = &migrate_nodes;
1752 	list_add(&stable_node_dup->list, stable_node_dup->head);
1753 	return page;
1754 
1755 chain_append:
1756 	/* stable_node_dup could be null if it reached the limit */
1757 	if (!stable_node_dup)
1758 		stable_node_dup = stable_node_any;
1759 	/*
1760 	 * If stable_node was a chain and chain_prune collapsed it,
1761 	 * stable_node has been updated to be the new regular
1762 	 * stable_node. A collapse of the chain is indistinguishable
1763 	 * from the case there was no chain in the stable
1764 	 * rbtree. Otherwise stable_node is the chain and
1765 	 * stable_node_dup is the dup to replace.
1766 	 */
1767 	if (stable_node_dup == stable_node) {
1768 		VM_BUG_ON(is_stable_node_dup(stable_node_dup));
1769 		/* chain is missing so create it */
1770 		stable_node = alloc_stable_node_chain(stable_node_dup,
1771 						      root);
1772 		if (!stable_node)
1773 			return NULL;
1774 	}
1775 	/*
1776 	 * Add this stable_node dup that was
1777 	 * migrated to the stable_node chain
1778 	 * of the current nid for this page
1779 	 * content.
1780 	 */
1781 	VM_BUG_ON(!is_stable_node_dup(stable_node_dup));
1782 	VM_BUG_ON(page_node->head != &migrate_nodes);
1783 	list_del(&page_node->list);
1784 	DO_NUMA(page_node->nid = nid);
1785 	stable_node_chain_add_dup(page_node, stable_node);
1786 	goto out;
1787 }
1788 
1789 /*
1790  * stable_tree_insert - insert stable tree node pointing to new ksm page
1791  * into the stable tree.
1792  *
1793  * This function returns the stable tree node just allocated on success,
1794  * NULL otherwise.
1795  */
stable_tree_insert(struct page * kpage)1796 static struct stable_node *stable_tree_insert(struct page *kpage)
1797 {
1798 	int nid;
1799 	unsigned long kpfn;
1800 	struct rb_root *root;
1801 	struct rb_node **new;
1802 	struct rb_node *parent;
1803 	struct stable_node *stable_node, *stable_node_dup, *stable_node_any;
1804 	bool need_chain = false;
1805 
1806 	kpfn = page_to_pfn(kpage);
1807 	nid = get_kpfn_nid(kpfn);
1808 	root = root_stable_tree + nid;
1809 again:
1810 	parent = NULL;
1811 	new = &root->rb_node;
1812 
1813 	while (*new) {
1814 		struct page *tree_page;
1815 		int ret;
1816 
1817 		cond_resched();
1818 		stable_node = rb_entry(*new, struct stable_node, node);
1819 		stable_node_any = NULL;
1820 		tree_page = chain(&stable_node_dup, stable_node, root);
1821 		if (!stable_node_dup) {
1822 			/*
1823 			 * Either all stable_node dups were full in
1824 			 * this stable_node chain, or this chain was
1825 			 * empty and should be rb_erased.
1826 			 */
1827 			stable_node_any = stable_node_dup_any(stable_node,
1828 							      root);
1829 			if (!stable_node_any) {
1830 				/* rb_erase just run */
1831 				goto again;
1832 			}
1833 			/*
1834 			 * Take any of the stable_node dups page of
1835 			 * this stable_node chain to let the tree walk
1836 			 * continue. All KSM pages belonging to the
1837 			 * stable_node dups in a stable_node chain
1838 			 * have the same content and they're
1839 			 * write protected at all times. Any will work
1840 			 * fine to continue the walk.
1841 			 */
1842 			tree_page = get_ksm_page(stable_node_any,
1843 						 GET_KSM_PAGE_NOLOCK);
1844 		}
1845 		VM_BUG_ON(!stable_node_dup ^ !!stable_node_any);
1846 		if (!tree_page) {
1847 			/*
1848 			 * If we walked over a stale stable_node,
1849 			 * get_ksm_page() will call rb_erase() and it
1850 			 * may rebalance the tree from under us. So
1851 			 * restart the search from scratch. Returning
1852 			 * NULL would be safe too, but we'd generate
1853 			 * false negative insertions just because some
1854 			 * stable_node was stale.
1855 			 */
1856 			goto again;
1857 		}
1858 
1859 		ret = memcmp_pages(kpage, tree_page);
1860 		put_page(tree_page);
1861 
1862 		parent = *new;
1863 		if (ret < 0)
1864 			new = &parent->rb_left;
1865 		else if (ret > 0)
1866 			new = &parent->rb_right;
1867 		else {
1868 			need_chain = true;
1869 			break;
1870 		}
1871 	}
1872 
1873 	stable_node_dup = alloc_stable_node();
1874 	if (!stable_node_dup)
1875 		return NULL;
1876 
1877 	INIT_HLIST_HEAD(&stable_node_dup->hlist);
1878 	stable_node_dup->kpfn = kpfn;
1879 	set_page_stable_node(kpage, stable_node_dup);
1880 	stable_node_dup->rmap_hlist_len = 0;
1881 	DO_NUMA(stable_node_dup->nid = nid);
1882 	if (!need_chain) {
1883 		rb_link_node(&stable_node_dup->node, parent, new);
1884 		rb_insert_color(&stable_node_dup->node, root);
1885 	} else {
1886 		if (!is_stable_node_chain(stable_node)) {
1887 			struct stable_node *orig = stable_node;
1888 			/* chain is missing so create it */
1889 			stable_node = alloc_stable_node_chain(orig, root);
1890 			if (!stable_node) {
1891 				free_stable_node(stable_node_dup);
1892 				return NULL;
1893 			}
1894 		}
1895 		stable_node_chain_add_dup(stable_node_dup, stable_node);
1896 	}
1897 
1898 	return stable_node_dup;
1899 }
1900 
1901 /*
1902  * unstable_tree_search_insert - search for identical page,
1903  * else insert rmap_item into the unstable tree.
1904  *
1905  * This function searches for a page in the unstable tree identical to the
1906  * page currently being scanned; and if no identical page is found in the
1907  * tree, we insert rmap_item as a new object into the unstable tree.
1908  *
1909  * This function returns pointer to rmap_item found to be identical
1910  * to the currently scanned page, NULL otherwise.
1911  *
1912  * This function does both searching and inserting, because they share
1913  * the same walking algorithm in an rbtree.
1914  */
1915 static
unstable_tree_search_insert(struct rmap_item * rmap_item,struct page * page,struct page ** tree_pagep)1916 struct rmap_item *unstable_tree_search_insert(struct rmap_item *rmap_item,
1917 					      struct page *page,
1918 					      struct page **tree_pagep)
1919 {
1920 	struct rb_node **new;
1921 	struct rb_root *root;
1922 	struct rb_node *parent = NULL;
1923 	int nid;
1924 
1925 	nid = get_kpfn_nid(page_to_pfn(page));
1926 	root = root_unstable_tree + nid;
1927 	new = &root->rb_node;
1928 
1929 	while (*new) {
1930 		struct rmap_item *tree_rmap_item;
1931 		struct page *tree_page;
1932 		int ret;
1933 
1934 		cond_resched();
1935 		tree_rmap_item = rb_entry(*new, struct rmap_item, node);
1936 		tree_page = get_mergeable_page(tree_rmap_item);
1937 		if (!tree_page)
1938 			return NULL;
1939 
1940 		/*
1941 		 * Don't substitute a ksm page for a forked page.
1942 		 */
1943 		if (page == tree_page) {
1944 			put_page(tree_page);
1945 			return NULL;
1946 		}
1947 
1948 		ret = memcmp_pages(page, tree_page);
1949 
1950 		parent = *new;
1951 		if (ret < 0) {
1952 			put_page(tree_page);
1953 			new = &parent->rb_left;
1954 		} else if (ret > 0) {
1955 			put_page(tree_page);
1956 			new = &parent->rb_right;
1957 		} else if (!ksm_merge_across_nodes &&
1958 			   page_to_nid(tree_page) != nid) {
1959 			/*
1960 			 * If tree_page has been migrated to another NUMA node,
1961 			 * it will be flushed out and put in the right unstable
1962 			 * tree next time: only merge with it when across_nodes.
1963 			 */
1964 			put_page(tree_page);
1965 			return NULL;
1966 		} else {
1967 			*tree_pagep = tree_page;
1968 			return tree_rmap_item;
1969 		}
1970 	}
1971 
1972 	rmap_item->address |= UNSTABLE_FLAG;
1973 	rmap_item->address |= (ksm_scan.seqnr & SEQNR_MASK);
1974 	DO_NUMA(rmap_item->nid = nid);
1975 	rb_link_node(&rmap_item->node, parent, new);
1976 	rb_insert_color(&rmap_item->node, root);
1977 
1978 	ksm_pages_unshared++;
1979 	return NULL;
1980 }
1981 
1982 /*
1983  * stable_tree_append - add another rmap_item to the linked list of
1984  * rmap_items hanging off a given node of the stable tree, all sharing
1985  * the same ksm page.
1986  */
stable_tree_append(struct rmap_item * rmap_item,struct stable_node * stable_node,bool max_page_sharing_bypass)1987 static void stable_tree_append(struct rmap_item *rmap_item,
1988 			       struct stable_node *stable_node,
1989 			       bool max_page_sharing_bypass)
1990 {
1991 	/*
1992 	 * rmap won't find this mapping if we don't insert the
1993 	 * rmap_item in the right stable_node
1994 	 * duplicate. page_migration could break later if rmap breaks,
1995 	 * so we can as well crash here. We really need to check for
1996 	 * rmap_hlist_len == STABLE_NODE_CHAIN, but we can as well check
1997 	 * for other negative values as an underflow if detected here
1998 	 * for the first time (and not when decreasing rmap_hlist_len)
1999 	 * would be sign of memory corruption in the stable_node.
2000 	 */
2001 	BUG_ON(stable_node->rmap_hlist_len < 0);
2002 
2003 	stable_node->rmap_hlist_len++;
2004 	if (!max_page_sharing_bypass)
2005 		/* possibly non fatal but unexpected overflow, only warn */
2006 		WARN_ON_ONCE(stable_node->rmap_hlist_len >
2007 			     ksm_max_page_sharing);
2008 
2009 	rmap_item->head = stable_node;
2010 	rmap_item->address |= STABLE_FLAG;
2011 	hlist_add_head(&rmap_item->hlist, &stable_node->hlist);
2012 
2013 	if (rmap_item->hlist.next)
2014 		ksm_pages_sharing++;
2015 	else
2016 		ksm_pages_shared++;
2017 }
2018 
2019 /*
2020  * cmp_and_merge_page - first see if page can be merged into the stable tree;
2021  * if not, compare checksum to previous and if it's the same, see if page can
2022  * be inserted into the unstable tree, or merged with a page already there and
2023  * both transferred to the stable tree.
2024  *
2025  * @page: the page that we are searching identical page to.
2026  * @rmap_item: the reverse mapping into the virtual address of this page
2027  */
cmp_and_merge_page(struct page * page,struct rmap_item * rmap_item)2028 static void cmp_and_merge_page(struct page *page, struct rmap_item *rmap_item)
2029 {
2030 	struct mm_struct *mm = rmap_item->mm;
2031 	struct rmap_item *tree_rmap_item;
2032 	struct page *tree_page = NULL;
2033 	struct stable_node *stable_node;
2034 	struct page *kpage;
2035 	unsigned int checksum;
2036 	int err;
2037 	bool max_page_sharing_bypass = false;
2038 
2039 	stable_node = page_stable_node(page);
2040 	if (stable_node) {
2041 		if (stable_node->head != &migrate_nodes &&
2042 		    get_kpfn_nid(READ_ONCE(stable_node->kpfn)) !=
2043 		    NUMA(stable_node->nid)) {
2044 			stable_node_dup_del(stable_node);
2045 			stable_node->head = &migrate_nodes;
2046 			list_add(&stable_node->list, stable_node->head);
2047 		}
2048 		if (stable_node->head != &migrate_nodes &&
2049 		    rmap_item->head == stable_node)
2050 			return;
2051 		/*
2052 		 * If it's a KSM fork, allow it to go over the sharing limit
2053 		 * without warnings.
2054 		 */
2055 		if (!is_page_sharing_candidate(stable_node))
2056 			max_page_sharing_bypass = true;
2057 	}
2058 
2059 	/* We first start with searching the page inside the stable tree */
2060 	kpage = stable_tree_search(page);
2061 	if (kpage == page && rmap_item->head == stable_node) {
2062 		put_page(kpage);
2063 		return;
2064 	}
2065 
2066 	remove_rmap_item_from_tree(rmap_item);
2067 
2068 	if (kpage) {
2069 		if (PTR_ERR(kpage) == -EBUSY)
2070 			return;
2071 
2072 		err = try_to_merge_with_ksm_page(rmap_item, page, kpage);
2073 		if (!err) {
2074 			/*
2075 			 * The page was successfully merged:
2076 			 * add its rmap_item to the stable tree.
2077 			 */
2078 			lock_page(kpage);
2079 			stable_tree_append(rmap_item, page_stable_node(kpage),
2080 					   max_page_sharing_bypass);
2081 			unlock_page(kpage);
2082 		}
2083 		put_page(kpage);
2084 		return;
2085 	}
2086 
2087 	/*
2088 	 * If the hash value of the page has changed from the last time
2089 	 * we calculated it, this page is changing frequently: therefore we
2090 	 * don't want to insert it in the unstable tree, and we don't want
2091 	 * to waste our time searching for something identical to it there.
2092 	 */
2093 	checksum = calc_checksum(page);
2094 	if (rmap_item->oldchecksum != checksum) {
2095 		rmap_item->oldchecksum = checksum;
2096 		return;
2097 	}
2098 
2099 	/*
2100 	 * Same checksum as an empty page. We attempt to merge it with the
2101 	 * appropriate zero page if the user enabled this via sysfs.
2102 	 */
2103 	if (ksm_use_zero_pages && (checksum == zero_checksum)) {
2104 		struct vm_area_struct *vma;
2105 
2106 		mmap_read_lock(mm);
2107 		vma = find_mergeable_vma(mm, rmap_item->address);
2108 		if (vma) {
2109 			err = try_to_merge_one_page(vma, page,
2110 					ZERO_PAGE(rmap_item->address));
2111 		} else {
2112 			/*
2113 			 * If the vma is out of date, we do not need to
2114 			 * continue.
2115 			 */
2116 			err = 0;
2117 		}
2118 		mmap_read_unlock(mm);
2119 		/*
2120 		 * In case of failure, the page was not really empty, so we
2121 		 * need to continue. Otherwise we're done.
2122 		 */
2123 		if (!err)
2124 			return;
2125 	}
2126 	tree_rmap_item =
2127 		unstable_tree_search_insert(rmap_item, page, &tree_page);
2128 	if (tree_rmap_item) {
2129 		bool split;
2130 
2131 		kpage = try_to_merge_two_pages(rmap_item, page,
2132 						tree_rmap_item, tree_page);
2133 		/*
2134 		 * If both pages we tried to merge belong to the same compound
2135 		 * page, then we actually ended up increasing the reference
2136 		 * count of the same compound page twice, and split_huge_page
2137 		 * failed.
2138 		 * Here we set a flag if that happened, and we use it later to
2139 		 * try split_huge_page again. Since we call put_page right
2140 		 * afterwards, the reference count will be correct and
2141 		 * split_huge_page should succeed.
2142 		 */
2143 		split = PageTransCompound(page)
2144 			&& compound_head(page) == compound_head(tree_page);
2145 		put_page(tree_page);
2146 		if (kpage) {
2147 			/*
2148 			 * The pages were successfully merged: insert new
2149 			 * node in the stable tree and add both rmap_items.
2150 			 */
2151 			lock_page(kpage);
2152 			stable_node = stable_tree_insert(kpage);
2153 			if (stable_node) {
2154 				stable_tree_append(tree_rmap_item, stable_node,
2155 						   false);
2156 				stable_tree_append(rmap_item, stable_node,
2157 						   false);
2158 			}
2159 			unlock_page(kpage);
2160 
2161 			/*
2162 			 * If we fail to insert the page into the stable tree,
2163 			 * we will have 2 virtual addresses that are pointing
2164 			 * to a ksm page left outside the stable tree,
2165 			 * in which case we need to break_cow on both.
2166 			 */
2167 			if (!stable_node) {
2168 				break_cow(tree_rmap_item);
2169 				break_cow(rmap_item);
2170 			}
2171 		} else if (split) {
2172 			/*
2173 			 * We are here if we tried to merge two pages and
2174 			 * failed because they both belonged to the same
2175 			 * compound page. We will split the page now, but no
2176 			 * merging will take place.
2177 			 * We do not want to add the cost of a full lock; if
2178 			 * the page is locked, it is better to skip it and
2179 			 * perhaps try again later.
2180 			 */
2181 			if (!trylock_page(page))
2182 				return;
2183 			split_huge_page(page);
2184 			unlock_page(page);
2185 		}
2186 	}
2187 }
2188 
get_next_rmap_item(struct mm_slot * mm_slot,struct rmap_item ** rmap_list,unsigned long addr)2189 static struct rmap_item *get_next_rmap_item(struct mm_slot *mm_slot,
2190 					    struct rmap_item **rmap_list,
2191 					    unsigned long addr)
2192 {
2193 	struct rmap_item *rmap_item;
2194 
2195 	while (*rmap_list) {
2196 		rmap_item = *rmap_list;
2197 		if ((rmap_item->address & PAGE_MASK) == addr)
2198 			return rmap_item;
2199 		if (rmap_item->address > addr)
2200 			break;
2201 		*rmap_list = rmap_item->rmap_list;
2202 		remove_rmap_item_from_tree(rmap_item);
2203 		free_rmap_item(rmap_item);
2204 	}
2205 
2206 	rmap_item = alloc_rmap_item();
2207 	if (rmap_item) {
2208 		/* It has already been zeroed */
2209 		rmap_item->mm = mm_slot->mm;
2210 		rmap_item->address = addr;
2211 		rmap_item->rmap_list = *rmap_list;
2212 		*rmap_list = rmap_item;
2213 	}
2214 	return rmap_item;
2215 }
2216 
scan_get_next_rmap_item(struct page ** page)2217 static struct rmap_item *scan_get_next_rmap_item(struct page **page)
2218 {
2219 	struct mm_struct *mm;
2220 	struct mm_slot *slot;
2221 	struct vm_area_struct *vma;
2222 	struct rmap_item *rmap_item;
2223 	int nid;
2224 
2225 	if (list_empty(&ksm_mm_head.mm_list))
2226 		return NULL;
2227 
2228 	slot = ksm_scan.mm_slot;
2229 	if (slot == &ksm_mm_head) {
2230 		/*
2231 		 * A number of pages can hang around indefinitely on per-cpu
2232 		 * pagevecs, raised page count preventing write_protect_page
2233 		 * from merging them.  Though it doesn't really matter much,
2234 		 * it is puzzling to see some stuck in pages_volatile until
2235 		 * other activity jostles them out, and they also prevented
2236 		 * LTP's KSM test from succeeding deterministically; so drain
2237 		 * them here (here rather than on entry to ksm_do_scan(),
2238 		 * so we don't IPI too often when pages_to_scan is set low).
2239 		 */
2240 		lru_add_drain_all();
2241 
2242 		/*
2243 		 * Whereas stale stable_nodes on the stable_tree itself
2244 		 * get pruned in the regular course of stable_tree_search(),
2245 		 * those moved out to the migrate_nodes list can accumulate:
2246 		 * so prune them once before each full scan.
2247 		 */
2248 		if (!ksm_merge_across_nodes) {
2249 			struct stable_node *stable_node, *next;
2250 			struct page *page;
2251 
2252 			list_for_each_entry_safe(stable_node, next,
2253 						 &migrate_nodes, list) {
2254 				page = get_ksm_page(stable_node,
2255 						    GET_KSM_PAGE_NOLOCK);
2256 				if (page)
2257 					put_page(page);
2258 				cond_resched();
2259 			}
2260 		}
2261 
2262 		for (nid = 0; nid < ksm_nr_node_ids; nid++)
2263 			root_unstable_tree[nid] = RB_ROOT;
2264 
2265 		spin_lock(&ksm_mmlist_lock);
2266 		slot = list_entry(slot->mm_list.next, struct mm_slot, mm_list);
2267 		ksm_scan.mm_slot = slot;
2268 		spin_unlock(&ksm_mmlist_lock);
2269 		/*
2270 		 * Although we tested list_empty() above, a racing __ksm_exit
2271 		 * of the last mm on the list may have removed it since then.
2272 		 */
2273 		if (slot == &ksm_mm_head)
2274 			return NULL;
2275 next_mm:
2276 		ksm_scan.address = 0;
2277 		ksm_scan.rmap_list = &slot->rmap_list;
2278 	}
2279 
2280 	mm = slot->mm;
2281 	mmap_read_lock(mm);
2282 	if (ksm_test_exit(mm))
2283 		vma = NULL;
2284 	else
2285 		vma = find_vma(mm, ksm_scan.address);
2286 
2287 	for (; vma; vma = vma->vm_next) {
2288 		if (!(vma->vm_flags & VM_MERGEABLE))
2289 			continue;
2290 		if (ksm_scan.address < vma->vm_start)
2291 			ksm_scan.address = vma->vm_start;
2292 		if (!vma->anon_vma)
2293 			ksm_scan.address = vma->vm_end;
2294 
2295 		while (ksm_scan.address < vma->vm_end) {
2296 			if (ksm_test_exit(mm))
2297 				break;
2298 			*page = follow_page(vma, ksm_scan.address, FOLL_GET);
2299 			if (IS_ERR_OR_NULL(*page)) {
2300 				ksm_scan.address += PAGE_SIZE;
2301 				cond_resched();
2302 				continue;
2303 			}
2304 			if (PageAnon(*page)) {
2305 				flush_anon_page(vma, *page, ksm_scan.address);
2306 				flush_dcache_page(*page);
2307 				rmap_item = get_next_rmap_item(slot,
2308 					ksm_scan.rmap_list, ksm_scan.address);
2309 				if (rmap_item) {
2310 					ksm_scan.rmap_list =
2311 							&rmap_item->rmap_list;
2312 					ksm_scan.address += PAGE_SIZE;
2313 				} else
2314 					put_page(*page);
2315 				mmap_read_unlock(mm);
2316 				return rmap_item;
2317 			}
2318 			put_page(*page);
2319 			ksm_scan.address += PAGE_SIZE;
2320 			cond_resched();
2321 		}
2322 	}
2323 
2324 	if (ksm_test_exit(mm)) {
2325 		ksm_scan.address = 0;
2326 		ksm_scan.rmap_list = &slot->rmap_list;
2327 	}
2328 	/*
2329 	 * Nuke all the rmap_items that are above this current rmap:
2330 	 * because there were no VM_MERGEABLE vmas with such addresses.
2331 	 */
2332 	remove_trailing_rmap_items(ksm_scan.rmap_list);
2333 
2334 	spin_lock(&ksm_mmlist_lock);
2335 	ksm_scan.mm_slot = list_entry(slot->mm_list.next,
2336 						struct mm_slot, mm_list);
2337 	if (ksm_scan.address == 0) {
2338 		/*
2339 		 * We've completed a full scan of all vmas, holding mmap_lock
2340 		 * throughout, and found no VM_MERGEABLE: so do the same as
2341 		 * __ksm_exit does to remove this mm from all our lists now.
2342 		 * This applies either when cleaning up after __ksm_exit
2343 		 * (but beware: we can reach here even before __ksm_exit),
2344 		 * or when all VM_MERGEABLE areas have been unmapped (and
2345 		 * mmap_lock then protects against race with MADV_MERGEABLE).
2346 		 */
2347 		hash_del(&slot->link);
2348 		list_del(&slot->mm_list);
2349 		spin_unlock(&ksm_mmlist_lock);
2350 
2351 		free_mm_slot(slot);
2352 		clear_bit(MMF_VM_MERGEABLE, &mm->flags);
2353 		mmap_read_unlock(mm);
2354 		mmdrop(mm);
2355 	} else {
2356 		mmap_read_unlock(mm);
2357 		/*
2358 		 * mmap_read_unlock(mm) first because after
2359 		 * spin_unlock(&ksm_mmlist_lock) run, the "mm" may
2360 		 * already have been freed under us by __ksm_exit()
2361 		 * because the "mm_slot" is still hashed and
2362 		 * ksm_scan.mm_slot doesn't point to it anymore.
2363 		 */
2364 		spin_unlock(&ksm_mmlist_lock);
2365 	}
2366 
2367 	/* Repeat until we've completed scanning the whole list */
2368 	slot = ksm_scan.mm_slot;
2369 	if (slot != &ksm_mm_head)
2370 		goto next_mm;
2371 
2372 	ksm_scan.seqnr++;
2373 	return NULL;
2374 }
2375 
2376 /**
2377  * ksm_do_scan  - the ksm scanner main worker function.
2378  * @scan_npages:  number of pages we want to scan before we return.
2379  */
ksm_do_scan(unsigned int scan_npages)2380 static void ksm_do_scan(unsigned int scan_npages)
2381 {
2382 	struct rmap_item *rmap_item;
2383 	struct page *page;
2384 
2385 	while (scan_npages-- && likely(!freezing(current))) {
2386 		cond_resched();
2387 		rmap_item = scan_get_next_rmap_item(&page);
2388 		if (!rmap_item)
2389 			return;
2390 		cmp_and_merge_page(page, rmap_item);
2391 		put_page(page);
2392 	}
2393 }
2394 
ksmd_should_run(void)2395 static int ksmd_should_run(void)
2396 {
2397 	return (ksm_run & KSM_RUN_MERGE) && !list_empty(&ksm_mm_head.mm_list);
2398 }
2399 
ksm_scan_thread(void * nothing)2400 static int ksm_scan_thread(void *nothing)
2401 {
2402 	unsigned int sleep_ms;
2403 
2404 	set_freezable();
2405 	set_user_nice(current, 5);
2406 
2407 	while (!kthread_should_stop()) {
2408 		mutex_lock(&ksm_thread_mutex);
2409 		wait_while_offlining();
2410 		if (ksmd_should_run())
2411 			ksm_do_scan(ksm_thread_pages_to_scan);
2412 		mutex_unlock(&ksm_thread_mutex);
2413 
2414 		try_to_freeze();
2415 
2416 		if (ksmd_should_run()) {
2417 			sleep_ms = READ_ONCE(ksm_thread_sleep_millisecs);
2418 			wait_event_interruptible_timeout(ksm_iter_wait,
2419 				sleep_ms != READ_ONCE(ksm_thread_sleep_millisecs),
2420 				msecs_to_jiffies(sleep_ms));
2421 		} else {
2422 			wait_event_freezable(ksm_thread_wait,
2423 				ksmd_should_run() || kthread_should_stop());
2424 		}
2425 	}
2426 	return 0;
2427 }
2428 
ksm_madvise(struct vm_area_struct * vma,unsigned long start,unsigned long end,int advice,unsigned long * vm_flags)2429 int ksm_madvise(struct vm_area_struct *vma, unsigned long start,
2430 		unsigned long end, int advice, unsigned long *vm_flags)
2431 {
2432 	struct mm_struct *mm = vma->vm_mm;
2433 	int err;
2434 
2435 	switch (advice) {
2436 	case MADV_MERGEABLE:
2437 		/*
2438 		 * Be somewhat over-protective for now!
2439 		 */
2440 		if (*vm_flags & (VM_MERGEABLE | VM_SHARED  | VM_MAYSHARE   |
2441 				 VM_PFNMAP    | VM_IO      | VM_DONTEXPAND |
2442 				 VM_HUGETLB | VM_MIXEDMAP))
2443 			return 0;		/* just ignore the advice */
2444 
2445 		if (vma_is_dax(vma))
2446 			return 0;
2447 
2448 #ifdef VM_SAO
2449 		if (*vm_flags & VM_SAO)
2450 			return 0;
2451 #endif
2452 #ifdef VM_SPARC_ADI
2453 		if (*vm_flags & VM_SPARC_ADI)
2454 			return 0;
2455 #endif
2456 
2457 		if (!test_bit(MMF_VM_MERGEABLE, &mm->flags)) {
2458 			err = __ksm_enter(mm);
2459 			if (err)
2460 				return err;
2461 		}
2462 
2463 		*vm_flags |= VM_MERGEABLE;
2464 		break;
2465 
2466 	case MADV_UNMERGEABLE:
2467 		if (!(*vm_flags & VM_MERGEABLE))
2468 			return 0;		/* just ignore the advice */
2469 
2470 		if (vma->anon_vma) {
2471 			err = unmerge_ksm_pages(vma, start, end);
2472 			if (err)
2473 				return err;
2474 		}
2475 
2476 		*vm_flags &= ~VM_MERGEABLE;
2477 		break;
2478 	}
2479 
2480 	return 0;
2481 }
2482 EXPORT_SYMBOL_GPL(ksm_madvise);
2483 
__ksm_enter(struct mm_struct * mm)2484 int __ksm_enter(struct mm_struct *mm)
2485 {
2486 	struct mm_slot *mm_slot;
2487 	int needs_wakeup;
2488 
2489 	mm_slot = alloc_mm_slot();
2490 	if (!mm_slot)
2491 		return -ENOMEM;
2492 
2493 	/* Check ksm_run too?  Would need tighter locking */
2494 	needs_wakeup = list_empty(&ksm_mm_head.mm_list);
2495 
2496 	spin_lock(&ksm_mmlist_lock);
2497 	insert_to_mm_slots_hash(mm, mm_slot);
2498 	/*
2499 	 * When KSM_RUN_MERGE (or KSM_RUN_STOP),
2500 	 * insert just behind the scanning cursor, to let the area settle
2501 	 * down a little; when fork is followed by immediate exec, we don't
2502 	 * want ksmd to waste time setting up and tearing down an rmap_list.
2503 	 *
2504 	 * But when KSM_RUN_UNMERGE, it's important to insert ahead of its
2505 	 * scanning cursor, otherwise KSM pages in newly forked mms will be
2506 	 * missed: then we might as well insert at the end of the list.
2507 	 */
2508 	if (ksm_run & KSM_RUN_UNMERGE)
2509 		list_add_tail(&mm_slot->mm_list, &ksm_mm_head.mm_list);
2510 	else
2511 		list_add_tail(&mm_slot->mm_list, &ksm_scan.mm_slot->mm_list);
2512 	spin_unlock(&ksm_mmlist_lock);
2513 
2514 	set_bit(MMF_VM_MERGEABLE, &mm->flags);
2515 	mmgrab(mm);
2516 
2517 	if (needs_wakeup)
2518 		wake_up_interruptible(&ksm_thread_wait);
2519 
2520 	return 0;
2521 }
2522 
__ksm_exit(struct mm_struct * mm)2523 void __ksm_exit(struct mm_struct *mm)
2524 {
2525 	struct mm_slot *mm_slot;
2526 	int easy_to_free = 0;
2527 
2528 	/*
2529 	 * This process is exiting: if it's straightforward (as is the
2530 	 * case when ksmd was never running), free mm_slot immediately.
2531 	 * But if it's at the cursor or has rmap_items linked to it, use
2532 	 * mmap_lock to synchronize with any break_cows before pagetables
2533 	 * are freed, and leave the mm_slot on the list for ksmd to free.
2534 	 * Beware: ksm may already have noticed it exiting and freed the slot.
2535 	 */
2536 
2537 	spin_lock(&ksm_mmlist_lock);
2538 	mm_slot = get_mm_slot(mm);
2539 	if (mm_slot && ksm_scan.mm_slot != mm_slot) {
2540 		if (!mm_slot->rmap_list) {
2541 			hash_del(&mm_slot->link);
2542 			list_del(&mm_slot->mm_list);
2543 			easy_to_free = 1;
2544 		} else {
2545 			list_move(&mm_slot->mm_list,
2546 				  &ksm_scan.mm_slot->mm_list);
2547 		}
2548 	}
2549 	spin_unlock(&ksm_mmlist_lock);
2550 
2551 	if (easy_to_free) {
2552 		free_mm_slot(mm_slot);
2553 		clear_bit(MMF_VM_MERGEABLE, &mm->flags);
2554 		mmdrop(mm);
2555 	} else if (mm_slot) {
2556 		mmap_write_lock(mm);
2557 		mmap_write_unlock(mm);
2558 	}
2559 }
2560 
ksm_might_need_to_copy(struct page * page,struct vm_area_struct * vma,unsigned long address)2561 struct page *ksm_might_need_to_copy(struct page *page,
2562 			struct vm_area_struct *vma, unsigned long address)
2563 {
2564 	struct anon_vma *anon_vma = page_anon_vma(page);
2565 	struct page *new_page;
2566 
2567 	if (PageKsm(page)) {
2568 		if (page_stable_node(page) &&
2569 		    !(ksm_run & KSM_RUN_UNMERGE))
2570 			return page;	/* no need to copy it */
2571 	} else if (!anon_vma) {
2572 		return page;		/* no need to copy it */
2573 	} else if (anon_vma->root == vma->anon_vma->root &&
2574 		 page->index == linear_page_index(vma, address)) {
2575 		return page;		/* still no need to copy it */
2576 	}
2577 	if (!PageUptodate(page))
2578 		return page;		/* let do_swap_page report the error */
2579 
2580 	new_page = alloc_page_vma(GFP_HIGHUSER_MOVABLE, vma, address);
2581 	if (new_page && mem_cgroup_charge(new_page, vma->vm_mm, GFP_KERNEL)) {
2582 		put_page(new_page);
2583 		new_page = NULL;
2584 	}
2585 	if (new_page) {
2586 		copy_user_highpage(new_page, page, address, vma);
2587 
2588 		SetPageDirty(new_page);
2589 		__SetPageUptodate(new_page);
2590 		__SetPageLocked(new_page);
2591 	}
2592 
2593 	return new_page;
2594 }
2595 
rmap_walk_ksm(struct page * page,struct rmap_walk_control * rwc)2596 void rmap_walk_ksm(struct page *page, struct rmap_walk_control *rwc)
2597 {
2598 	struct stable_node *stable_node;
2599 	struct rmap_item *rmap_item;
2600 	int search_new_forks = 0;
2601 
2602 	VM_BUG_ON_PAGE(!PageKsm(page), page);
2603 
2604 	/*
2605 	 * Rely on the page lock to protect against concurrent modifications
2606 	 * to that page's node of the stable tree.
2607 	 */
2608 	VM_BUG_ON_PAGE(!PageLocked(page), page);
2609 
2610 	stable_node = page_stable_node(page);
2611 	if (!stable_node)
2612 		return;
2613 again:
2614 	hlist_for_each_entry(rmap_item, &stable_node->hlist, hlist) {
2615 		struct anon_vma *anon_vma = rmap_item->anon_vma;
2616 		struct anon_vma_chain *vmac;
2617 		struct vm_area_struct *vma;
2618 
2619 		cond_resched();
2620 		if (!anon_vma_trylock_read(anon_vma)) {
2621 			if (rwc->try_lock) {
2622 				rwc->contended = true;
2623 				return;
2624 			}
2625 			anon_vma_lock_read(anon_vma);
2626 		}
2627 		anon_vma_interval_tree_foreach(vmac, &anon_vma->rb_root,
2628 					       0, ULONG_MAX) {
2629 			unsigned long addr;
2630 
2631 			cond_resched();
2632 			vma = vmac->vma;
2633 
2634 			/* Ignore the stable/unstable/sqnr flags */
2635 			addr = rmap_item->address & PAGE_MASK;
2636 
2637 			if (addr < vma->vm_start || addr >= vma->vm_end)
2638 				continue;
2639 			/*
2640 			 * Initially we examine only the vma which covers this
2641 			 * rmap_item; but later, if there is still work to do,
2642 			 * we examine covering vmas in other mms: in case they
2643 			 * were forked from the original since ksmd passed.
2644 			 */
2645 			if ((rmap_item->mm == vma->vm_mm) == search_new_forks)
2646 				continue;
2647 
2648 			if (rwc->invalid_vma && rwc->invalid_vma(vma, rwc->arg))
2649 				continue;
2650 
2651 			if (!rwc->rmap_one(page, vma, addr, rwc->arg)) {
2652 				anon_vma_unlock_read(anon_vma);
2653 				return;
2654 			}
2655 			if (rwc->done && rwc->done(page)) {
2656 				anon_vma_unlock_read(anon_vma);
2657 				return;
2658 			}
2659 		}
2660 		anon_vma_unlock_read(anon_vma);
2661 	}
2662 	if (!search_new_forks++)
2663 		goto again;
2664 }
2665 
2666 #ifdef CONFIG_MIGRATION
ksm_migrate_page(struct page * newpage,struct page * oldpage)2667 void ksm_migrate_page(struct page *newpage, struct page *oldpage)
2668 {
2669 	struct stable_node *stable_node;
2670 
2671 	VM_BUG_ON_PAGE(!PageLocked(oldpage), oldpage);
2672 	VM_BUG_ON_PAGE(!PageLocked(newpage), newpage);
2673 	VM_BUG_ON_PAGE(newpage->mapping != oldpage->mapping, newpage);
2674 
2675 	stable_node = page_stable_node(newpage);
2676 	if (stable_node) {
2677 		VM_BUG_ON_PAGE(stable_node->kpfn != page_to_pfn(oldpage), oldpage);
2678 		stable_node->kpfn = page_to_pfn(newpage);
2679 		/*
2680 		 * newpage->mapping was set in advance; now we need smp_wmb()
2681 		 * to make sure that the new stable_node->kpfn is visible
2682 		 * to get_ksm_page() before it can see that oldpage->mapping
2683 		 * has gone stale (or that PageSwapCache has been cleared).
2684 		 */
2685 		smp_wmb();
2686 		set_page_stable_node(oldpage, NULL);
2687 	}
2688 }
2689 #endif /* CONFIG_MIGRATION */
2690 
2691 #ifdef CONFIG_MEMORY_HOTREMOVE
wait_while_offlining(void)2692 static void wait_while_offlining(void)
2693 {
2694 	while (ksm_run & KSM_RUN_OFFLINE) {
2695 		mutex_unlock(&ksm_thread_mutex);
2696 		wait_on_bit(&ksm_run, ilog2(KSM_RUN_OFFLINE),
2697 			    TASK_UNINTERRUPTIBLE);
2698 		mutex_lock(&ksm_thread_mutex);
2699 	}
2700 }
2701 
stable_node_dup_remove_range(struct stable_node * stable_node,unsigned long start_pfn,unsigned long end_pfn)2702 static bool stable_node_dup_remove_range(struct stable_node *stable_node,
2703 					 unsigned long start_pfn,
2704 					 unsigned long end_pfn)
2705 {
2706 	if (stable_node->kpfn >= start_pfn &&
2707 	    stable_node->kpfn < end_pfn) {
2708 		/*
2709 		 * Don't get_ksm_page, page has already gone:
2710 		 * which is why we keep kpfn instead of page*
2711 		 */
2712 		remove_node_from_stable_tree(stable_node);
2713 		return true;
2714 	}
2715 	return false;
2716 }
2717 
stable_node_chain_remove_range(struct stable_node * stable_node,unsigned long start_pfn,unsigned long end_pfn,struct rb_root * root)2718 static bool stable_node_chain_remove_range(struct stable_node *stable_node,
2719 					   unsigned long start_pfn,
2720 					   unsigned long end_pfn,
2721 					   struct rb_root *root)
2722 {
2723 	struct stable_node *dup;
2724 	struct hlist_node *hlist_safe;
2725 
2726 	if (!is_stable_node_chain(stable_node)) {
2727 		VM_BUG_ON(is_stable_node_dup(stable_node));
2728 		return stable_node_dup_remove_range(stable_node, start_pfn,
2729 						    end_pfn);
2730 	}
2731 
2732 	hlist_for_each_entry_safe(dup, hlist_safe,
2733 				  &stable_node->hlist, hlist_dup) {
2734 		VM_BUG_ON(!is_stable_node_dup(dup));
2735 		stable_node_dup_remove_range(dup, start_pfn, end_pfn);
2736 	}
2737 	if (hlist_empty(&stable_node->hlist)) {
2738 		free_stable_node_chain(stable_node, root);
2739 		return true; /* notify caller that tree was rebalanced */
2740 	} else
2741 		return false;
2742 }
2743 
ksm_check_stable_tree(unsigned long start_pfn,unsigned long end_pfn)2744 static void ksm_check_stable_tree(unsigned long start_pfn,
2745 				  unsigned long end_pfn)
2746 {
2747 	struct stable_node *stable_node, *next;
2748 	struct rb_node *node;
2749 	int nid;
2750 
2751 	for (nid = 0; nid < ksm_nr_node_ids; nid++) {
2752 		node = rb_first(root_stable_tree + nid);
2753 		while (node) {
2754 			stable_node = rb_entry(node, struct stable_node, node);
2755 			if (stable_node_chain_remove_range(stable_node,
2756 							   start_pfn, end_pfn,
2757 							   root_stable_tree +
2758 							   nid))
2759 				node = rb_first(root_stable_tree + nid);
2760 			else
2761 				node = rb_next(node);
2762 			cond_resched();
2763 		}
2764 	}
2765 	list_for_each_entry_safe(stable_node, next, &migrate_nodes, list) {
2766 		if (stable_node->kpfn >= start_pfn &&
2767 		    stable_node->kpfn < end_pfn)
2768 			remove_node_from_stable_tree(stable_node);
2769 		cond_resched();
2770 	}
2771 }
2772 
ksm_memory_callback(struct notifier_block * self,unsigned long action,void * arg)2773 static int ksm_memory_callback(struct notifier_block *self,
2774 			       unsigned long action, void *arg)
2775 {
2776 	struct memory_notify *mn = arg;
2777 
2778 	switch (action) {
2779 	case MEM_GOING_OFFLINE:
2780 		/*
2781 		 * Prevent ksm_do_scan(), unmerge_and_remove_all_rmap_items()
2782 		 * and remove_all_stable_nodes() while memory is going offline:
2783 		 * it is unsafe for them to touch the stable tree at this time.
2784 		 * But unmerge_ksm_pages(), rmap lookups and other entry points
2785 		 * which do not need the ksm_thread_mutex are all safe.
2786 		 */
2787 		mutex_lock(&ksm_thread_mutex);
2788 		ksm_run |= KSM_RUN_OFFLINE;
2789 		mutex_unlock(&ksm_thread_mutex);
2790 		break;
2791 
2792 	case MEM_OFFLINE:
2793 		/*
2794 		 * Most of the work is done by page migration; but there might
2795 		 * be a few stable_nodes left over, still pointing to struct
2796 		 * pages which have been offlined: prune those from the tree,
2797 		 * otherwise get_ksm_page() might later try to access a
2798 		 * non-existent struct page.
2799 		 */
2800 		ksm_check_stable_tree(mn->start_pfn,
2801 				      mn->start_pfn + mn->nr_pages);
2802 		fallthrough;
2803 	case MEM_CANCEL_OFFLINE:
2804 		mutex_lock(&ksm_thread_mutex);
2805 		ksm_run &= ~KSM_RUN_OFFLINE;
2806 		mutex_unlock(&ksm_thread_mutex);
2807 
2808 		smp_mb();	/* wake_up_bit advises this */
2809 		wake_up_bit(&ksm_run, ilog2(KSM_RUN_OFFLINE));
2810 		break;
2811 	}
2812 	return NOTIFY_OK;
2813 }
2814 #else
wait_while_offlining(void)2815 static void wait_while_offlining(void)
2816 {
2817 }
2818 #endif /* CONFIG_MEMORY_HOTREMOVE */
2819 
2820 #ifdef CONFIG_SYSFS
2821 /*
2822  * This all compiles without CONFIG_SYSFS, but is a waste of space.
2823  */
2824 
2825 #define KSM_ATTR_RO(_name) \
2826 	static struct kobj_attribute _name##_attr = __ATTR_RO(_name)
2827 #define KSM_ATTR(_name) \
2828 	static struct kobj_attribute _name##_attr = \
2829 		__ATTR(_name, 0644, _name##_show, _name##_store)
2830 
sleep_millisecs_show(struct kobject * kobj,struct kobj_attribute * attr,char * buf)2831 static ssize_t sleep_millisecs_show(struct kobject *kobj,
2832 				    struct kobj_attribute *attr, char *buf)
2833 {
2834 	return sysfs_emit(buf, "%u\n", ksm_thread_sleep_millisecs);
2835 }
2836 
sleep_millisecs_store(struct kobject * kobj,struct kobj_attribute * attr,const char * buf,size_t count)2837 static ssize_t sleep_millisecs_store(struct kobject *kobj,
2838 				     struct kobj_attribute *attr,
2839 				     const char *buf, size_t count)
2840 {
2841 	unsigned int msecs;
2842 	int err;
2843 
2844 	err = kstrtouint(buf, 10, &msecs);
2845 	if (err)
2846 		return -EINVAL;
2847 
2848 	ksm_thread_sleep_millisecs = msecs;
2849 	wake_up_interruptible(&ksm_iter_wait);
2850 
2851 	return count;
2852 }
2853 KSM_ATTR(sleep_millisecs);
2854 
pages_to_scan_show(struct kobject * kobj,struct kobj_attribute * attr,char * buf)2855 static ssize_t pages_to_scan_show(struct kobject *kobj,
2856 				  struct kobj_attribute *attr, char *buf)
2857 {
2858 	return sysfs_emit(buf, "%u\n", ksm_thread_pages_to_scan);
2859 }
2860 
pages_to_scan_store(struct kobject * kobj,struct kobj_attribute * attr,const char * buf,size_t count)2861 static ssize_t pages_to_scan_store(struct kobject *kobj,
2862 				   struct kobj_attribute *attr,
2863 				   const char *buf, size_t count)
2864 {
2865 	unsigned int nr_pages;
2866 	int err;
2867 
2868 	err = kstrtouint(buf, 10, &nr_pages);
2869 	if (err)
2870 		return -EINVAL;
2871 
2872 	ksm_thread_pages_to_scan = nr_pages;
2873 
2874 	return count;
2875 }
2876 KSM_ATTR(pages_to_scan);
2877 
run_show(struct kobject * kobj,struct kobj_attribute * attr,char * buf)2878 static ssize_t run_show(struct kobject *kobj, struct kobj_attribute *attr,
2879 			char *buf)
2880 {
2881 	return sysfs_emit(buf, "%lu\n", ksm_run);
2882 }
2883 
run_store(struct kobject * kobj,struct kobj_attribute * attr,const char * buf,size_t count)2884 static ssize_t run_store(struct kobject *kobj, struct kobj_attribute *attr,
2885 			 const char *buf, size_t count)
2886 {
2887 	unsigned int flags;
2888 	int err;
2889 
2890 	err = kstrtouint(buf, 10, &flags);
2891 	if (err)
2892 		return -EINVAL;
2893 	if (flags > KSM_RUN_UNMERGE)
2894 		return -EINVAL;
2895 
2896 	/*
2897 	 * KSM_RUN_MERGE sets ksmd running, and 0 stops it running.
2898 	 * KSM_RUN_UNMERGE stops it running and unmerges all rmap_items,
2899 	 * breaking COW to free the pages_shared (but leaves mm_slots
2900 	 * on the list for when ksmd may be set running again).
2901 	 */
2902 
2903 	mutex_lock(&ksm_thread_mutex);
2904 	wait_while_offlining();
2905 	if (ksm_run != flags) {
2906 		ksm_run = flags;
2907 		if (flags & KSM_RUN_UNMERGE) {
2908 			set_current_oom_origin();
2909 			err = unmerge_and_remove_all_rmap_items();
2910 			clear_current_oom_origin();
2911 			if (err) {
2912 				ksm_run = KSM_RUN_STOP;
2913 				count = err;
2914 			}
2915 		}
2916 	}
2917 	mutex_unlock(&ksm_thread_mutex);
2918 
2919 	if (flags & KSM_RUN_MERGE)
2920 		wake_up_interruptible(&ksm_thread_wait);
2921 
2922 	return count;
2923 }
2924 KSM_ATTR(run);
2925 
2926 #ifdef CONFIG_NUMA
merge_across_nodes_show(struct kobject * kobj,struct kobj_attribute * attr,char * buf)2927 static ssize_t merge_across_nodes_show(struct kobject *kobj,
2928 				       struct kobj_attribute *attr, char *buf)
2929 {
2930 	return sysfs_emit(buf, "%u\n", ksm_merge_across_nodes);
2931 }
2932 
merge_across_nodes_store(struct kobject * kobj,struct kobj_attribute * attr,const char * buf,size_t count)2933 static ssize_t merge_across_nodes_store(struct kobject *kobj,
2934 				   struct kobj_attribute *attr,
2935 				   const char *buf, size_t count)
2936 {
2937 	int err;
2938 	unsigned long knob;
2939 
2940 	err = kstrtoul(buf, 10, &knob);
2941 	if (err)
2942 		return err;
2943 	if (knob > 1)
2944 		return -EINVAL;
2945 
2946 	mutex_lock(&ksm_thread_mutex);
2947 	wait_while_offlining();
2948 	if (ksm_merge_across_nodes != knob) {
2949 		if (ksm_pages_shared || remove_all_stable_nodes())
2950 			err = -EBUSY;
2951 		else if (root_stable_tree == one_stable_tree) {
2952 			struct rb_root *buf;
2953 			/*
2954 			 * This is the first time that we switch away from the
2955 			 * default of merging across nodes: must now allocate
2956 			 * a buffer to hold as many roots as may be needed.
2957 			 * Allocate stable and unstable together:
2958 			 * MAXSMP NODES_SHIFT 10 will use 16kB.
2959 			 */
2960 			buf = kcalloc(nr_node_ids + nr_node_ids, sizeof(*buf),
2961 				      GFP_KERNEL);
2962 			/* Let us assume that RB_ROOT is NULL is zero */
2963 			if (!buf)
2964 				err = -ENOMEM;
2965 			else {
2966 				root_stable_tree = buf;
2967 				root_unstable_tree = buf + nr_node_ids;
2968 				/* Stable tree is empty but not the unstable */
2969 				root_unstable_tree[0] = one_unstable_tree[0];
2970 			}
2971 		}
2972 		if (!err) {
2973 			ksm_merge_across_nodes = knob;
2974 			ksm_nr_node_ids = knob ? 1 : nr_node_ids;
2975 		}
2976 	}
2977 	mutex_unlock(&ksm_thread_mutex);
2978 
2979 	return err ? err : count;
2980 }
2981 KSM_ATTR(merge_across_nodes);
2982 #endif
2983 
use_zero_pages_show(struct kobject * kobj,struct kobj_attribute * attr,char * buf)2984 static ssize_t use_zero_pages_show(struct kobject *kobj,
2985 				   struct kobj_attribute *attr, char *buf)
2986 {
2987 	return sysfs_emit(buf, "%u\n", ksm_use_zero_pages);
2988 }
use_zero_pages_store(struct kobject * kobj,struct kobj_attribute * attr,const char * buf,size_t count)2989 static ssize_t use_zero_pages_store(struct kobject *kobj,
2990 				   struct kobj_attribute *attr,
2991 				   const char *buf, size_t count)
2992 {
2993 	int err;
2994 	bool value;
2995 
2996 	err = kstrtobool(buf, &value);
2997 	if (err)
2998 		return -EINVAL;
2999 
3000 	ksm_use_zero_pages = value;
3001 
3002 	return count;
3003 }
3004 KSM_ATTR(use_zero_pages);
3005 
max_page_sharing_show(struct kobject * kobj,struct kobj_attribute * attr,char * buf)3006 static ssize_t max_page_sharing_show(struct kobject *kobj,
3007 				     struct kobj_attribute *attr, char *buf)
3008 {
3009 	return sysfs_emit(buf, "%u\n", ksm_max_page_sharing);
3010 }
3011 
max_page_sharing_store(struct kobject * kobj,struct kobj_attribute * attr,const char * buf,size_t count)3012 static ssize_t max_page_sharing_store(struct kobject *kobj,
3013 				      struct kobj_attribute *attr,
3014 				      const char *buf, size_t count)
3015 {
3016 	int err;
3017 	int knob;
3018 
3019 	err = kstrtoint(buf, 10, &knob);
3020 	if (err)
3021 		return err;
3022 	/*
3023 	 * When a KSM page is created it is shared by 2 mappings. This
3024 	 * being a signed comparison, it implicitly verifies it's not
3025 	 * negative.
3026 	 */
3027 	if (knob < 2)
3028 		return -EINVAL;
3029 
3030 	if (READ_ONCE(ksm_max_page_sharing) == knob)
3031 		return count;
3032 
3033 	mutex_lock(&ksm_thread_mutex);
3034 	wait_while_offlining();
3035 	if (ksm_max_page_sharing != knob) {
3036 		if (ksm_pages_shared || remove_all_stable_nodes())
3037 			err = -EBUSY;
3038 		else
3039 			ksm_max_page_sharing = knob;
3040 	}
3041 	mutex_unlock(&ksm_thread_mutex);
3042 
3043 	return err ? err : count;
3044 }
3045 KSM_ATTR(max_page_sharing);
3046 
pages_shared_show(struct kobject * kobj,struct kobj_attribute * attr,char * buf)3047 static ssize_t pages_shared_show(struct kobject *kobj,
3048 				 struct kobj_attribute *attr, char *buf)
3049 {
3050 	return sysfs_emit(buf, "%lu\n", ksm_pages_shared);
3051 }
3052 KSM_ATTR_RO(pages_shared);
3053 
pages_sharing_show(struct kobject * kobj,struct kobj_attribute * attr,char * buf)3054 static ssize_t pages_sharing_show(struct kobject *kobj,
3055 				  struct kobj_attribute *attr, char *buf)
3056 {
3057 	return sysfs_emit(buf, "%lu\n", ksm_pages_sharing);
3058 }
3059 KSM_ATTR_RO(pages_sharing);
3060 
pages_unshared_show(struct kobject * kobj,struct kobj_attribute * attr,char * buf)3061 static ssize_t pages_unshared_show(struct kobject *kobj,
3062 				   struct kobj_attribute *attr, char *buf)
3063 {
3064 	return sysfs_emit(buf, "%lu\n", ksm_pages_unshared);
3065 }
3066 KSM_ATTR_RO(pages_unshared);
3067 
pages_volatile_show(struct kobject * kobj,struct kobj_attribute * attr,char * buf)3068 static ssize_t pages_volatile_show(struct kobject *kobj,
3069 				   struct kobj_attribute *attr, char *buf)
3070 {
3071 	long ksm_pages_volatile;
3072 
3073 	ksm_pages_volatile = ksm_rmap_items - ksm_pages_shared
3074 				- ksm_pages_sharing - ksm_pages_unshared;
3075 	/*
3076 	 * It was not worth any locking to calculate that statistic,
3077 	 * but it might therefore sometimes be negative: conceal that.
3078 	 */
3079 	if (ksm_pages_volatile < 0)
3080 		ksm_pages_volatile = 0;
3081 	return sysfs_emit(buf, "%ld\n", ksm_pages_volatile);
3082 }
3083 KSM_ATTR_RO(pages_volatile);
3084 
stable_node_dups_show(struct kobject * kobj,struct kobj_attribute * attr,char * buf)3085 static ssize_t stable_node_dups_show(struct kobject *kobj,
3086 				     struct kobj_attribute *attr, char *buf)
3087 {
3088 	return sysfs_emit(buf, "%lu\n", ksm_stable_node_dups);
3089 }
3090 KSM_ATTR_RO(stable_node_dups);
3091 
stable_node_chains_show(struct kobject * kobj,struct kobj_attribute * attr,char * buf)3092 static ssize_t stable_node_chains_show(struct kobject *kobj,
3093 				       struct kobj_attribute *attr, char *buf)
3094 {
3095 	return sysfs_emit(buf, "%lu\n", ksm_stable_node_chains);
3096 }
3097 KSM_ATTR_RO(stable_node_chains);
3098 
3099 static ssize_t
stable_node_chains_prune_millisecs_show(struct kobject * kobj,struct kobj_attribute * attr,char * buf)3100 stable_node_chains_prune_millisecs_show(struct kobject *kobj,
3101 					struct kobj_attribute *attr,
3102 					char *buf)
3103 {
3104 	return sysfs_emit(buf, "%u\n", ksm_stable_node_chains_prune_millisecs);
3105 }
3106 
3107 static ssize_t
stable_node_chains_prune_millisecs_store(struct kobject * kobj,struct kobj_attribute * attr,const char * buf,size_t count)3108 stable_node_chains_prune_millisecs_store(struct kobject *kobj,
3109 					 struct kobj_attribute *attr,
3110 					 const char *buf, size_t count)
3111 {
3112 	unsigned int msecs;
3113 	int err;
3114 
3115 	err = kstrtouint(buf, 10, &msecs);
3116 	if (err)
3117 		return -EINVAL;
3118 
3119 	ksm_stable_node_chains_prune_millisecs = msecs;
3120 
3121 	return count;
3122 }
3123 KSM_ATTR(stable_node_chains_prune_millisecs);
3124 
full_scans_show(struct kobject * kobj,struct kobj_attribute * attr,char * buf)3125 static ssize_t full_scans_show(struct kobject *kobj,
3126 			       struct kobj_attribute *attr, char *buf)
3127 {
3128 	return sysfs_emit(buf, "%lu\n", ksm_scan.seqnr);
3129 }
3130 KSM_ATTR_RO(full_scans);
3131 
3132 static struct attribute *ksm_attrs[] = {
3133 	&sleep_millisecs_attr.attr,
3134 	&pages_to_scan_attr.attr,
3135 	&run_attr.attr,
3136 	&pages_shared_attr.attr,
3137 	&pages_sharing_attr.attr,
3138 	&pages_unshared_attr.attr,
3139 	&pages_volatile_attr.attr,
3140 	&full_scans_attr.attr,
3141 #ifdef CONFIG_NUMA
3142 	&merge_across_nodes_attr.attr,
3143 #endif
3144 	&max_page_sharing_attr.attr,
3145 	&stable_node_chains_attr.attr,
3146 	&stable_node_dups_attr.attr,
3147 	&stable_node_chains_prune_millisecs_attr.attr,
3148 	&use_zero_pages_attr.attr,
3149 	NULL,
3150 };
3151 
3152 static const struct attribute_group ksm_attr_group = {
3153 	.attrs = ksm_attrs,
3154 	.name = "ksm",
3155 };
3156 #endif /* CONFIG_SYSFS */
3157 
ksm_init(void)3158 static int __init ksm_init(void)
3159 {
3160 	struct task_struct *ksm_thread;
3161 	int err;
3162 
3163 	/* The correct value depends on page size and endianness */
3164 	zero_checksum = calc_checksum(ZERO_PAGE(0));
3165 	/* Default to false for backwards compatibility */
3166 	ksm_use_zero_pages = false;
3167 
3168 	err = ksm_slab_init();
3169 	if (err)
3170 		goto out;
3171 
3172 	ksm_thread = kthread_run(ksm_scan_thread, NULL, "ksmd");
3173 	if (IS_ERR(ksm_thread)) {
3174 		pr_err("ksm: creating kthread failed\n");
3175 		err = PTR_ERR(ksm_thread);
3176 		goto out_free;
3177 	}
3178 
3179 #ifdef CONFIG_SYSFS
3180 	err = sysfs_create_group(mm_kobj, &ksm_attr_group);
3181 	if (err) {
3182 		pr_err("ksm: register sysfs failed\n");
3183 		kthread_stop(ksm_thread);
3184 		goto out_free;
3185 	}
3186 #else
3187 	ksm_run = KSM_RUN_MERGE;	/* no way for user to start it */
3188 
3189 #endif /* CONFIG_SYSFS */
3190 
3191 #ifdef CONFIG_MEMORY_HOTREMOVE
3192 	/* There is no significance to this priority 100 */
3193 	hotplug_memory_notifier(ksm_memory_callback, 100);
3194 #endif
3195 	return 0;
3196 
3197 out_free:
3198 	ksm_slab_free();
3199 out:
3200 	return err;
3201 }
3202 subsys_initcall(ksm_init);
3203