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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 | /* |
103 | * Setting frontswap_ops must happen after the ops->init() calls | |
104 | * above; cmpxchg implies smp_mb() which will ensure the init is | |
105 | * complete at this point. | |
106 | */ | |
107 | do { | |
108 | ops->next = frontswap_ops; | |
109 | } while (cmpxchg(&frontswap_ops, ops->next, ops) != ops->next); | |
110 | ||
8ea1d2a1 | 111 | static_branch_inc(&frontswap_enabled_key); |
29f233cf | 112 | } |
29f233cf | 113 | |
29f233cf DM |
114 | /* |
115 | * Called when a swap device is swapon'd. | |
116 | */ | |
1cf53c89 | 117 | void frontswap_init(unsigned type, unsigned long *map) |
29f233cf DM |
118 | { |
119 | struct swap_info_struct *sis = swap_info[type]; | |
d1dc6f1b | 120 | struct frontswap_ops *ops; |
29f233cf | 121 | |
8ea1d2a1 | 122 | VM_BUG_ON(sis == NULL); |
4f89849d MK |
123 | |
124 | /* | |
125 | * p->frontswap is a bitmap that we MUST have to figure out which page | |
126 | * has gone in frontswap. Without it there is no point of continuing. | |
127 | */ | |
128 | if (WARN_ON(!map)) | |
129 | return; | |
130 | /* | |
131 | * Irregardless of whether the frontswap backend has been loaded | |
132 | * before this function or it will be later, we _MUST_ have the | |
133 | * p->frontswap set to something valid to work properly. | |
134 | */ | |
135 | frontswap_map_set(sis, map); | |
d1dc6f1b DS |
136 | |
137 | for_each_frontswap_ops(ops) | |
138 | ops->init(type); | |
29f233cf | 139 | } |
29f233cf | 140 | |
bd9cd521 | 141 | static bool __frontswap_test(struct swap_info_struct *sis, |
f066ea23 BL |
142 | pgoff_t offset) |
143 | { | |
d1dc6f1b DS |
144 | if (sis->frontswap_map) |
145 | return test_bit(offset, sis->frontswap_map); | |
146 | return false; | |
f066ea23 | 147 | } |
f066ea23 | 148 | |
d1dc6f1b DS |
149 | static inline void __frontswap_set(struct swap_info_struct *sis, |
150 | pgoff_t offset) | |
151 | { | |
152 | set_bit(offset, sis->frontswap_map); | |
153 | atomic_inc(&sis->frontswap_pages); | |
154 | } | |
155 | ||
f066ea23 | 156 | static inline void __frontswap_clear(struct swap_info_struct *sis, |
d1dc6f1b | 157 | pgoff_t offset) |
611edfed | 158 | { |
f066ea23 | 159 | clear_bit(offset, sis->frontswap_map); |
611edfed SL |
160 | atomic_dec(&sis->frontswap_pages); |
161 | } | |
162 | ||
29f233cf | 163 | /* |
165c8aed | 164 | * "Store" data from a page to frontswap and associate it with the page's |
29f233cf DM |
165 | * swaptype and offset. Page must be locked and in the swap cache. |
166 | * If frontswap already contains a page with matching swaptype and | |
1d00015e | 167 | * offset, the frontswap implementation may either overwrite the data and |
29f233cf DM |
168 | * return success or invalidate the page from frontswap and return failure. |
169 | */ | |
165c8aed | 170 | int __frontswap_store(struct page *page) |
29f233cf | 171 | { |
d1dc6f1b | 172 | int ret = -1; |
29f233cf DM |
173 | swp_entry_t entry = { .val = page_private(page), }; |
174 | int type = swp_type(entry); | |
175 | struct swap_info_struct *sis = swap_info[type]; | |
176 | pgoff_t offset = swp_offset(entry); | |
d1dc6f1b | 177 | struct frontswap_ops *ops; |
29f233cf | 178 | |
8ea1d2a1 VB |
179 | VM_BUG_ON(!frontswap_ops); |
180 | VM_BUG_ON(!PageLocked(page)); | |
181 | VM_BUG_ON(sis == NULL); | |
d1dc6f1b DS |
182 | |
183 | /* | |
184 | * If a dup, we must remove the old page first; we can't leave the | |
185 | * old page no matter if the store of the new page succeeds or fails, | |
186 | * and we can't rely on the new page replacing the old page as we may | |
187 | * not store to the same implementation that contains the old page. | |
188 | */ | |
189 | if (__frontswap_test(sis, offset)) { | |
190 | __frontswap_clear(sis, offset); | |
191 | for_each_frontswap_ops(ops) | |
192 | ops->invalidate_page(type, offset); | |
193 | } | |
194 | ||
195 | /* Try to store in each implementation, until one succeeds. */ | |
196 | for_each_frontswap_ops(ops) { | |
197 | ret = ops->store(type, offset, page); | |
198 | if (!ret) /* successful store */ | |
199 | break; | |
200 | } | |
29f233cf | 201 | if (ret == 0) { |
d1dc6f1b | 202 | __frontswap_set(sis, offset); |
165c8aed | 203 | inc_frontswap_succ_stores(); |
d9674dda | 204 | } else { |
165c8aed | 205 | inc_frontswap_failed_stores(); |
4bb3e31e | 206 | } |
3d6035f1 | 207 | |
29f233cf DM |
208 | return ret; |
209 | } | |
29f233cf DM |
210 | |
211 | /* | |
212 | * "Get" data from frontswap associated with swaptype and offset that were | |
213 | * specified when the data was put to frontswap and use it to fill the | |
214 | * specified page with data. Page must be locked and in the swap cache. | |
215 | */ | |
165c8aed | 216 | int __frontswap_load(struct page *page) |
29f233cf DM |
217 | { |
218 | int ret = -1; | |
219 | swp_entry_t entry = { .val = page_private(page), }; | |
220 | int type = swp_type(entry); | |
221 | struct swap_info_struct *sis = swap_info[type]; | |
222 | pgoff_t offset = swp_offset(entry); | |
d1dc6f1b DS |
223 | struct frontswap_ops *ops; |
224 | ||
8ea1d2a1 VB |
225 | VM_BUG_ON(!frontswap_ops); |
226 | VM_BUG_ON(!PageLocked(page)); | |
227 | VM_BUG_ON(sis == NULL); | |
29f233cf | 228 | |
d1dc6f1b DS |
229 | if (!__frontswap_test(sis, offset)) |
230 | return -1; | |
231 | ||
232 | /* Try loading from each implementation, until one succeeds. */ | |
233 | for_each_frontswap_ops(ops) { | |
234 | ret = ops->load(type, offset, page); | |
235 | if (!ret) /* successful load */ | |
236 | break; | |
237 | } | |
71024cb4 | 238 | if (ret == 0) |
165c8aed | 239 | inc_frontswap_loads(); |
29f233cf DM |
240 | return ret; |
241 | } | |
29f233cf DM |
242 | |
243 | /* | |
244 | * Invalidate any data from frontswap associated with the specified swaptype | |
245 | * and offset so that a subsequent "get" will fail. | |
246 | */ | |
247 | void __frontswap_invalidate_page(unsigned type, pgoff_t offset) | |
248 | { | |
249 | struct swap_info_struct *sis = swap_info[type]; | |
d1dc6f1b DS |
250 | struct frontswap_ops *ops; |
251 | ||
8ea1d2a1 VB |
252 | VM_BUG_ON(!frontswap_ops); |
253 | VM_BUG_ON(sis == NULL); | |
29f233cf | 254 | |
d1dc6f1b DS |
255 | if (!__frontswap_test(sis, offset)) |
256 | return; | |
257 | ||
258 | for_each_frontswap_ops(ops) | |
259 | ops->invalidate_page(type, offset); | |
260 | __frontswap_clear(sis, offset); | |
261 | inc_frontswap_invalidates(); | |
29f233cf | 262 | } |
29f233cf DM |
263 | |
264 | /* | |
265 | * Invalidate all data from frontswap associated with all offsets for the | |
266 | * specified swaptype. | |
267 | */ | |
268 | void __frontswap_invalidate_area(unsigned type) | |
269 | { | |
270 | struct swap_info_struct *sis = swap_info[type]; | |
d1dc6f1b | 271 | struct frontswap_ops *ops; |
29f233cf | 272 | |
8ea1d2a1 VB |
273 | VM_BUG_ON(!frontswap_ops); |
274 | VM_BUG_ON(sis == NULL); | |
d1dc6f1b | 275 | |
d1dc6f1b DS |
276 | if (sis->frontswap_map == NULL) |
277 | return; | |
278 | ||
279 | for_each_frontswap_ops(ops) | |
280 | ops->invalidate_area(type); | |
281 | atomic_set(&sis->frontswap_pages, 0); | |
282 | bitmap_zero(sis->frontswap_map, sis->max); | |
29f233cf | 283 | } |
29f233cf | 284 | |
29f233cf DM |
285 | static int __init init_frontswap(void) |
286 | { | |
287 | #ifdef CONFIG_DEBUG_FS | |
288 | struct dentry *root = debugfs_create_dir("frontswap", NULL); | |
289 | if (root == NULL) | |
290 | return -ENXIO; | |
0825a6f9 JP |
291 | debugfs_create_u64("loads", 0444, root, &frontswap_loads); |
292 | debugfs_create_u64("succ_stores", 0444, root, &frontswap_succ_stores); | |
293 | debugfs_create_u64("failed_stores", 0444, root, | |
294 | &frontswap_failed_stores); | |
295 | debugfs_create_u64("invalidates", 0444, root, &frontswap_invalidates); | |
29f233cf DM |
296 | #endif |
297 | return 0; | |
298 | } | |
299 | ||
300 | module_init(init_frontswap); |