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7a338472 | 1 | // SPDX-License-Identifier: GPL-2.0-only |
29f233cf DM |
2 | /* |
3 | * Frontswap frontend | |
4 | * | |
5 | * This code provides the generic "frontend" layer to call a matching | |
6 | * "backend" driver implementation of frontswap. See | |
ad56b738 | 7 | * Documentation/vm/frontswap.rst for more information. |
29f233cf DM |
8 | * |
9 | * Copyright (C) 2009-2012 Oracle Corp. All rights reserved. | |
10 | * Author: Dan Magenheimer | |
29f233cf DM |
11 | */ |
12 | ||
29f233cf DM |
13 | #include <linux/mman.h> |
14 | #include <linux/swap.h> | |
15 | #include <linux/swapops.h> | |
29f233cf | 16 | #include <linux/security.h> |
29f233cf | 17 | #include <linux/module.h> |
29f233cf DM |
18 | #include <linux/debugfs.h> |
19 | #include <linux/frontswap.h> | |
20 | #include <linux/swapfile.h> | |
21 | ||
8ea1d2a1 VB |
22 | DEFINE_STATIC_KEY_FALSE(frontswap_enabled_key); |
23 | ||
29f233cf | 24 | /* |
d1dc6f1b DS |
25 | * frontswap_ops are added by frontswap_register_ops, and provide the |
26 | * frontswap "backend" implementation functions. Multiple implementations | |
27 | * may be registered, but implementations can never deregister. This | |
28 | * is a simple singly-linked list of all registered implementations. | |
29f233cf | 29 | */ |
1e01c968 | 30 | static struct frontswap_ops *frontswap_ops __read_mostly; |
29f233cf | 31 | |
d1dc6f1b DS |
32 | #define for_each_frontswap_ops(ops) \ |
33 | for ((ops) = frontswap_ops; (ops); (ops) = (ops)->next) | |
34 | ||
29f233cf DM |
35 | #ifdef CONFIG_DEBUG_FS |
36 | /* | |
37 | * Counters available via /sys/kernel/debug/frontswap (if debugfs is | |
38 | * properly configured). These are for information only so are not protected | |
39 | * against increment races. | |
40 | */ | |
165c8aed KRW |
41 | static u64 frontswap_loads; |
42 | static u64 frontswap_succ_stores; | |
43 | static u64 frontswap_failed_stores; | |
29f233cf DM |
44 | static u64 frontswap_invalidates; |
45 | ||
68d68ff6 ZD |
46 | static inline void inc_frontswap_loads(void) |
47 | { | |
96bdd2bc | 48 | data_race(frontswap_loads++); |
29f233cf | 49 | } |
68d68ff6 ZD |
50 | static inline void inc_frontswap_succ_stores(void) |
51 | { | |
96bdd2bc | 52 | data_race(frontswap_succ_stores++); |
29f233cf | 53 | } |
68d68ff6 ZD |
54 | static inline void inc_frontswap_failed_stores(void) |
55 | { | |
96bdd2bc | 56 | data_race(frontswap_failed_stores++); |
29f233cf | 57 | } |
68d68ff6 ZD |
58 | static inline void inc_frontswap_invalidates(void) |
59 | { | |
96bdd2bc | 60 | data_race(frontswap_invalidates++); |
29f233cf DM |
61 | } |
62 | #else | |
165c8aed KRW |
63 | static inline void inc_frontswap_loads(void) { } |
64 | static inline void inc_frontswap_succ_stores(void) { } | |
65 | static inline void inc_frontswap_failed_stores(void) { } | |
29f233cf DM |
66 | static inline void inc_frontswap_invalidates(void) { } |
67 | #endif | |
905cd0e1 DM |
68 | |
69 | /* | |
70 | * Due to the asynchronous nature of the backends loading potentially | |
71 | * _after_ the swap system has been activated, we have chokepoints | |
72 | * on all frontswap functions to not call the backend until the backend | |
73 | * has registered. | |
74 | * | |
905cd0e1 DM |
75 | * This would not guards us against the user deciding to call swapoff right as |
76 | * we are calling the backend to initialize (so swapon is in action). | |
404f3ecf | 77 | * Fortunately for us, the swapon_mutex has been taken by the callee so we are |
905cd0e1 DM |
78 | * OK. The other scenario where calls to frontswap_store (called via |
79 | * swap_writepage) is racing with frontswap_invalidate_area (called via | |
80 | * swapoff) is again guarded by the swap subsystem. | |
81 | * | |
82 | * While no backend is registered all calls to frontswap_[store|load| | |
83 | * invalidate_area|invalidate_page] are ignored or fail. | |
84 | * | |
85 | * The time between the backend being registered and the swap file system | |
86 | * calling the backend (via the frontswap_* functions) is indeterminate as | |
1e01c968 | 87 | * frontswap_ops is not atomic_t (or a value guarded by a spinlock). |
905cd0e1 DM |
88 | * That is OK as we are comfortable missing some of these calls to the newly |
89 | * registered backend. | |
90 | * | |
91 | * Obviously the opposite (unloading the backend) must be done after all | |
92 | * the frontswap_[store|load|invalidate_area|invalidate_page] start | |
d1dc6f1b DS |
93 | * ignoring or failing the requests. However, there is currently no way |
94 | * to unload a backend once it is registered. | |
905cd0e1 | 95 | */ |
905cd0e1 | 96 | |
29f233cf | 97 | /* |
d1dc6f1b | 98 | * Register operations for frontswap |
29f233cf | 99 | */ |
d1dc6f1b | 100 | void frontswap_register_ops(struct frontswap_ops *ops) |
29f233cf | 101 | { |
d1dc6f1b DS |
102 | DECLARE_BITMAP(a, MAX_SWAPFILES); |
103 | DECLARE_BITMAP(b, MAX_SWAPFILES); | |
104 | struct swap_info_struct *si; | |
105 | unsigned int i; | |
106 | ||
107 | bitmap_zero(a, MAX_SWAPFILES); | |
108 | bitmap_zero(b, MAX_SWAPFILES); | |
109 | ||
110 | spin_lock(&swap_lock); | |
111 | plist_for_each_entry(si, &swap_active_head, list) { | |
112 | if (!WARN_ON(!si->frontswap_map)) | |
3795f46b | 113 | __set_bit(si->type, a); |
d1dc6f1b DS |
114 | } |
115 | spin_unlock(&swap_lock); | |
116 | ||
117 | /* the new ops needs to know the currently active swap devices */ | |
118 | for_each_set_bit(i, a, MAX_SWAPFILES) | |
119 | ops->init(i); | |
120 | ||
121 | /* | |
122 | * Setting frontswap_ops must happen after the ops->init() calls | |
123 | * above; cmpxchg implies smp_mb() which will ensure the init is | |
124 | * complete at this point. | |
125 | */ | |
126 | do { | |
127 | ops->next = frontswap_ops; | |
128 | } while (cmpxchg(&frontswap_ops, ops->next, ops) != ops->next); | |
129 | ||
8ea1d2a1 VB |
130 | static_branch_inc(&frontswap_enabled_key); |
131 | ||
d1dc6f1b DS |
132 | spin_lock(&swap_lock); |
133 | plist_for_each_entry(si, &swap_active_head, list) { | |
134 | if (si->frontswap_map) | |
3795f46b | 135 | __set_bit(si->type, b); |
905cd0e1 | 136 | } |
d1dc6f1b DS |
137 | spin_unlock(&swap_lock); |
138 | ||
905cd0e1 | 139 | /* |
d1dc6f1b DS |
140 | * On the very unlikely chance that a swap device was added or |
141 | * removed between setting the "a" list bits and the ops init | |
142 | * calls, we re-check and do init or invalidate for any changed | |
143 | * bits. | |
905cd0e1 | 144 | */ |
d1dc6f1b DS |
145 | if (unlikely(!bitmap_equal(a, b, MAX_SWAPFILES))) { |
146 | for (i = 0; i < MAX_SWAPFILES; i++) { | |
147 | if (!test_bit(i, a) && test_bit(i, b)) | |
148 | ops->init(i); | |
149 | else if (test_bit(i, a) && !test_bit(i, b)) | |
150 | ops->invalidate_area(i); | |
151 | } | |
152 | } | |
29f233cf DM |
153 | } |
154 | EXPORT_SYMBOL(frontswap_register_ops); | |
155 | ||
29f233cf DM |
156 | /* |
157 | * Called when a swap device is swapon'd. | |
158 | */ | |
1cf53c89 | 159 | void frontswap_init(unsigned type, unsigned long *map) |
29f233cf DM |
160 | { |
161 | struct swap_info_struct *sis = swap_info[type]; | |
d1dc6f1b | 162 | struct frontswap_ops *ops; |
29f233cf | 163 | |
8ea1d2a1 | 164 | VM_BUG_ON(sis == NULL); |
4f89849d MK |
165 | |
166 | /* | |
167 | * p->frontswap is a bitmap that we MUST have to figure out which page | |
168 | * has gone in frontswap. Without it there is no point of continuing. | |
169 | */ | |
170 | if (WARN_ON(!map)) | |
171 | return; | |
172 | /* | |
173 | * Irregardless of whether the frontswap backend has been loaded | |
174 | * before this function or it will be later, we _MUST_ have the | |
175 | * p->frontswap set to something valid to work properly. | |
176 | */ | |
177 | frontswap_map_set(sis, map); | |
d1dc6f1b DS |
178 | |
179 | for_each_frontswap_ops(ops) | |
180 | ops->init(type); | |
29f233cf | 181 | } |
29f233cf | 182 | |
f066ea23 BL |
183 | bool __frontswap_test(struct swap_info_struct *sis, |
184 | pgoff_t offset) | |
185 | { | |
d1dc6f1b DS |
186 | if (sis->frontswap_map) |
187 | return test_bit(offset, sis->frontswap_map); | |
188 | return false; | |
f066ea23 BL |
189 | } |
190 | EXPORT_SYMBOL(__frontswap_test); | |
191 | ||
d1dc6f1b DS |
192 | static inline void __frontswap_set(struct swap_info_struct *sis, |
193 | pgoff_t offset) | |
194 | { | |
195 | set_bit(offset, sis->frontswap_map); | |
196 | atomic_inc(&sis->frontswap_pages); | |
197 | } | |
198 | ||
f066ea23 | 199 | static inline void __frontswap_clear(struct swap_info_struct *sis, |
d1dc6f1b | 200 | pgoff_t offset) |
611edfed | 201 | { |
f066ea23 | 202 | clear_bit(offset, sis->frontswap_map); |
611edfed SL |
203 | atomic_dec(&sis->frontswap_pages); |
204 | } | |
205 | ||
29f233cf | 206 | /* |
165c8aed | 207 | * "Store" data from a page to frontswap and associate it with the page's |
29f233cf DM |
208 | * swaptype and offset. Page must be locked and in the swap cache. |
209 | * If frontswap already contains a page with matching swaptype and | |
1d00015e | 210 | * offset, the frontswap implementation may either overwrite the data and |
29f233cf DM |
211 | * return success or invalidate the page from frontswap and return failure. |
212 | */ | |
165c8aed | 213 | int __frontswap_store(struct page *page) |
29f233cf | 214 | { |
d1dc6f1b | 215 | int ret = -1; |
29f233cf DM |
216 | swp_entry_t entry = { .val = page_private(page), }; |
217 | int type = swp_type(entry); | |
218 | struct swap_info_struct *sis = swap_info[type]; | |
219 | pgoff_t offset = swp_offset(entry); | |
d1dc6f1b | 220 | struct frontswap_ops *ops; |
29f233cf | 221 | |
8ea1d2a1 VB |
222 | VM_BUG_ON(!frontswap_ops); |
223 | VM_BUG_ON(!PageLocked(page)); | |
224 | VM_BUG_ON(sis == NULL); | |
d1dc6f1b DS |
225 | |
226 | /* | |
227 | * If a dup, we must remove the old page first; we can't leave the | |
228 | * old page no matter if the store of the new page succeeds or fails, | |
229 | * and we can't rely on the new page replacing the old page as we may | |
230 | * not store to the same implementation that contains the old page. | |
231 | */ | |
232 | if (__frontswap_test(sis, offset)) { | |
233 | __frontswap_clear(sis, offset); | |
234 | for_each_frontswap_ops(ops) | |
235 | ops->invalidate_page(type, offset); | |
236 | } | |
237 | ||
238 | /* Try to store in each implementation, until one succeeds. */ | |
239 | for_each_frontswap_ops(ops) { | |
240 | ret = ops->store(type, offset, page); | |
241 | if (!ret) /* successful store */ | |
242 | break; | |
243 | } | |
29f233cf | 244 | if (ret == 0) { |
d1dc6f1b | 245 | __frontswap_set(sis, offset); |
165c8aed | 246 | inc_frontswap_succ_stores(); |
d9674dda | 247 | } else { |
165c8aed | 248 | inc_frontswap_failed_stores(); |
4bb3e31e | 249 | } |
3d6035f1 | 250 | |
29f233cf DM |
251 | return ret; |
252 | } | |
165c8aed | 253 | EXPORT_SYMBOL(__frontswap_store); |
29f233cf DM |
254 | |
255 | /* | |
256 | * "Get" data from frontswap associated with swaptype and offset that were | |
257 | * specified when the data was put to frontswap and use it to fill the | |
258 | * specified page with data. Page must be locked and in the swap cache. | |
259 | */ | |
165c8aed | 260 | int __frontswap_load(struct page *page) |
29f233cf DM |
261 | { |
262 | int ret = -1; | |
263 | swp_entry_t entry = { .val = page_private(page), }; | |
264 | int type = swp_type(entry); | |
265 | struct swap_info_struct *sis = swap_info[type]; | |
266 | pgoff_t offset = swp_offset(entry); | |
d1dc6f1b DS |
267 | struct frontswap_ops *ops; |
268 | ||
8ea1d2a1 VB |
269 | VM_BUG_ON(!frontswap_ops); |
270 | VM_BUG_ON(!PageLocked(page)); | |
271 | VM_BUG_ON(sis == NULL); | |
29f233cf | 272 | |
d1dc6f1b DS |
273 | if (!__frontswap_test(sis, offset)) |
274 | return -1; | |
275 | ||
276 | /* Try loading from each implementation, until one succeeds. */ | |
277 | for_each_frontswap_ops(ops) { | |
278 | ret = ops->load(type, offset, page); | |
279 | if (!ret) /* successful load */ | |
280 | break; | |
281 | } | |
71024cb4 | 282 | if (ret == 0) |
165c8aed | 283 | inc_frontswap_loads(); |
29f233cf DM |
284 | return ret; |
285 | } | |
165c8aed | 286 | EXPORT_SYMBOL(__frontswap_load); |
29f233cf DM |
287 | |
288 | /* | |
289 | * Invalidate any data from frontswap associated with the specified swaptype | |
290 | * and offset so that a subsequent "get" will fail. | |
291 | */ | |
292 | void __frontswap_invalidate_page(unsigned type, pgoff_t offset) | |
293 | { | |
294 | struct swap_info_struct *sis = swap_info[type]; | |
d1dc6f1b DS |
295 | struct frontswap_ops *ops; |
296 | ||
8ea1d2a1 VB |
297 | VM_BUG_ON(!frontswap_ops); |
298 | VM_BUG_ON(sis == NULL); | |
29f233cf | 299 | |
d1dc6f1b DS |
300 | if (!__frontswap_test(sis, offset)) |
301 | return; | |
302 | ||
303 | for_each_frontswap_ops(ops) | |
304 | ops->invalidate_page(type, offset); | |
305 | __frontswap_clear(sis, offset); | |
306 | inc_frontswap_invalidates(); | |
29f233cf DM |
307 | } |
308 | EXPORT_SYMBOL(__frontswap_invalidate_page); | |
309 | ||
310 | /* | |
311 | * Invalidate all data from frontswap associated with all offsets for the | |
312 | * specified swaptype. | |
313 | */ | |
314 | void __frontswap_invalidate_area(unsigned type) | |
315 | { | |
316 | struct swap_info_struct *sis = swap_info[type]; | |
d1dc6f1b | 317 | struct frontswap_ops *ops; |
29f233cf | 318 | |
8ea1d2a1 VB |
319 | VM_BUG_ON(!frontswap_ops); |
320 | VM_BUG_ON(sis == NULL); | |
d1dc6f1b | 321 | |
d1dc6f1b DS |
322 | if (sis->frontswap_map == NULL) |
323 | return; | |
324 | ||
325 | for_each_frontswap_ops(ops) | |
326 | ops->invalidate_area(type); | |
327 | atomic_set(&sis->frontswap_pages, 0); | |
328 | bitmap_zero(sis->frontswap_map, sis->max); | |
29f233cf DM |
329 | } |
330 | EXPORT_SYMBOL(__frontswap_invalidate_area); | |
331 | ||
29f233cf DM |
332 | static int __init init_frontswap(void) |
333 | { | |
334 | #ifdef CONFIG_DEBUG_FS | |
335 | struct dentry *root = debugfs_create_dir("frontswap", NULL); | |
336 | if (root == NULL) | |
337 | return -ENXIO; | |
0825a6f9 JP |
338 | debugfs_create_u64("loads", 0444, root, &frontswap_loads); |
339 | debugfs_create_u64("succ_stores", 0444, root, &frontswap_succ_stores); | |
340 | debugfs_create_u64("failed_stores", 0444, root, | |
341 | &frontswap_failed_stores); | |
342 | debugfs_create_u64("invalidates", 0444, root, &frontswap_invalidates); | |
29f233cf DM |
343 | #endif |
344 | return 0; | |
345 | } | |
346 | ||
347 | module_init(init_frontswap); |