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1 | // SPDX-License-Identifier: GPL-2.0-only | |
2 | /* | |
3 | * Frontswap frontend | |
4 | * | |
5 | * This code provides the generic "frontend" layer to call a matching | |
6 | * "backend" driver implementation of frontswap. See | |
7 | * Documentation/mm/frontswap.rst for more information. | |
8 | * | |
9 | * Copyright (C) 2009-2012 Oracle Corp. All rights reserved. | |
10 | * Author: Dan Magenheimer | |
11 | */ | |
12 | ||
13 | #include <linux/mman.h> | |
14 | #include <linux/swap.h> | |
15 | #include <linux/swapops.h> | |
16 | #include <linux/security.h> | |
17 | #include <linux/module.h> | |
18 | #include <linux/debugfs.h> | |
19 | #include <linux/frontswap.h> | |
20 | #include <linux/swapfile.h> | |
21 | ||
22 | DEFINE_STATIC_KEY_FALSE(frontswap_enabled_key); | |
23 | ||
24 | /* | |
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. | |
29 | */ | |
30 | static const struct frontswap_ops *frontswap_ops __read_mostly; | |
31 | ||
32 | #ifdef CONFIG_DEBUG_FS | |
33 | /* | |
34 | * Counters available via /sys/kernel/debug/frontswap (if debugfs is | |
35 | * properly configured). These are for information only so are not protected | |
36 | * against increment races. | |
37 | */ | |
38 | static u64 frontswap_loads; | |
39 | static u64 frontswap_succ_stores; | |
40 | static u64 frontswap_failed_stores; | |
41 | static u64 frontswap_invalidates; | |
42 | ||
43 | static inline void inc_frontswap_loads(void) | |
44 | { | |
45 | data_race(frontswap_loads++); | |
46 | } | |
47 | static inline void inc_frontswap_succ_stores(void) | |
48 | { | |
49 | data_race(frontswap_succ_stores++); | |
50 | } | |
51 | static inline void inc_frontswap_failed_stores(void) | |
52 | { | |
53 | data_race(frontswap_failed_stores++); | |
54 | } | |
55 | static inline void inc_frontswap_invalidates(void) | |
56 | { | |
57 | data_race(frontswap_invalidates++); | |
58 | } | |
59 | #else | |
60 | static inline void inc_frontswap_loads(void) { } | |
61 | static inline void inc_frontswap_succ_stores(void) { } | |
62 | static inline void inc_frontswap_failed_stores(void) { } | |
63 | static inline void inc_frontswap_invalidates(void) { } | |
64 | #endif | |
65 | ||
66 | /* | |
67 | * Due to the asynchronous nature of the backends loading potentially | |
68 | * _after_ the swap system has been activated, we have chokepoints | |
69 | * on all frontswap functions to not call the backend until the backend | |
70 | * has registered. | |
71 | * | |
72 | * This would not guards us against the user deciding to call swapoff right as | |
73 | * we are calling the backend to initialize (so swapon is in action). | |
74 | * Fortunately for us, the swapon_mutex has been taken by the callee so we are | |
75 | * OK. The other scenario where calls to frontswap_store (called via | |
76 | * swap_writepage) is racing with frontswap_invalidate_area (called via | |
77 | * swapoff) is again guarded by the swap subsystem. | |
78 | * | |
79 | * While no backend is registered all calls to frontswap_[store|load| | |
80 | * invalidate_area|invalidate_page] are ignored or fail. | |
81 | * | |
82 | * The time between the backend being registered and the swap file system | |
83 | * calling the backend (via the frontswap_* functions) is indeterminate as | |
84 | * frontswap_ops is not atomic_t (or a value guarded by a spinlock). | |
85 | * That is OK as we are comfortable missing some of these calls to the newly | |
86 | * registered backend. | |
87 | * | |
88 | * Obviously the opposite (unloading the backend) must be done after all | |
89 | * the frontswap_[store|load|invalidate_area|invalidate_page] start | |
90 | * ignoring or failing the requests. However, there is currently no way | |
91 | * to unload a backend once it is registered. | |
92 | */ | |
93 | ||
94 | /* | |
95 | * Register operations for frontswap | |
96 | */ | |
97 | int frontswap_register_ops(const struct frontswap_ops *ops) | |
98 | { | |
99 | if (frontswap_ops) | |
100 | return -EINVAL; | |
101 | ||
102 | frontswap_ops = ops; | |
103 | static_branch_inc(&frontswap_enabled_key); | |
104 | return 0; | |
105 | } | |
106 | ||
107 | /* | |
108 | * Called when a swap device is swapon'd. | |
109 | */ | |
110 | void frontswap_init(unsigned type, unsigned long *map) | |
111 | { | |
112 | struct swap_info_struct *sis = swap_info[type]; | |
113 | ||
114 | VM_BUG_ON(sis == NULL); | |
115 | ||
116 | /* | |
117 | * p->frontswap is a bitmap that we MUST have to figure out which page | |
118 | * has gone in frontswap. Without it there is no point of continuing. | |
119 | */ | |
120 | if (WARN_ON(!map)) | |
121 | return; | |
122 | /* | |
123 | * Irregardless of whether the frontswap backend has been loaded | |
124 | * before this function or it will be later, we _MUST_ have the | |
125 | * p->frontswap set to something valid to work properly. | |
126 | */ | |
127 | frontswap_map_set(sis, map); | |
128 | ||
129 | if (!frontswap_enabled()) | |
130 | return; | |
131 | frontswap_ops->init(type); | |
132 | } | |
133 | ||
134 | static bool __frontswap_test(struct swap_info_struct *sis, | |
135 | pgoff_t offset) | |
136 | { | |
137 | if (sis->frontswap_map) | |
138 | return test_bit(offset, sis->frontswap_map); | |
139 | return false; | |
140 | } | |
141 | ||
142 | static inline void __frontswap_set(struct swap_info_struct *sis, | |
143 | pgoff_t offset) | |
144 | { | |
145 | set_bit(offset, sis->frontswap_map); | |
146 | atomic_inc(&sis->frontswap_pages); | |
147 | } | |
148 | ||
149 | static inline void __frontswap_clear(struct swap_info_struct *sis, | |
150 | pgoff_t offset) | |
151 | { | |
152 | clear_bit(offset, sis->frontswap_map); | |
153 | atomic_dec(&sis->frontswap_pages); | |
154 | } | |
155 | ||
156 | /* | |
157 | * "Store" data from a page to frontswap and associate it with the page's | |
158 | * swaptype and offset. Page must be locked and in the swap cache. | |
159 | * If frontswap already contains a page with matching swaptype and | |
160 | * offset, the frontswap implementation may either overwrite the data and | |
161 | * return success or invalidate the page from frontswap and return failure. | |
162 | */ | |
163 | int __frontswap_store(struct page *page) | |
164 | { | |
165 | int ret = -1; | |
166 | swp_entry_t entry = { .val = page_private(page), }; | |
167 | int type = swp_type(entry); | |
168 | struct swap_info_struct *sis = swap_info[type]; | |
169 | pgoff_t offset = swp_offset(entry); | |
170 | ||
171 | VM_BUG_ON(!frontswap_ops); | |
172 | VM_BUG_ON(!PageLocked(page)); | |
173 | VM_BUG_ON(sis == NULL); | |
174 | ||
175 | /* | |
176 | * If a dup, we must remove the old page first; we can't leave the | |
177 | * old page no matter if the store of the new page succeeds or fails, | |
178 | * and we can't rely on the new page replacing the old page as we may | |
179 | * not store to the same implementation that contains the old page. | |
180 | */ | |
181 | if (__frontswap_test(sis, offset)) { | |
182 | __frontswap_clear(sis, offset); | |
183 | frontswap_ops->invalidate_page(type, offset); | |
184 | } | |
185 | ||
186 | ret = frontswap_ops->store(type, offset, page); | |
187 | if (ret == 0) { | |
188 | __frontswap_set(sis, offset); | |
189 | inc_frontswap_succ_stores(); | |
190 | } else { | |
191 | inc_frontswap_failed_stores(); | |
192 | } | |
193 | ||
194 | return ret; | |
195 | } | |
196 | ||
197 | /* | |
198 | * "Get" data from frontswap associated with swaptype and offset that were | |
199 | * specified when the data was put to frontswap and use it to fill the | |
200 | * specified page with data. Page must be locked and in the swap cache. | |
201 | */ | |
202 | int __frontswap_load(struct page *page) | |
203 | { | |
204 | int ret = -1; | |
205 | swp_entry_t entry = { .val = page_private(page), }; | |
206 | int type = swp_type(entry); | |
207 | struct swap_info_struct *sis = swap_info[type]; | |
208 | pgoff_t offset = swp_offset(entry); | |
209 | ||
210 | VM_BUG_ON(!frontswap_ops); | |
211 | VM_BUG_ON(!PageLocked(page)); | |
212 | VM_BUG_ON(sis == NULL); | |
213 | ||
214 | if (!__frontswap_test(sis, offset)) | |
215 | return -1; | |
216 | ||
217 | /* Try loading from each implementation, until one succeeds. */ | |
218 | ret = frontswap_ops->load(type, offset, page); | |
219 | if (ret == 0) | |
220 | inc_frontswap_loads(); | |
221 | return ret; | |
222 | } | |
223 | ||
224 | /* | |
225 | * Invalidate any data from frontswap associated with the specified swaptype | |
226 | * and offset so that a subsequent "get" will fail. | |
227 | */ | |
228 | void __frontswap_invalidate_page(unsigned type, pgoff_t offset) | |
229 | { | |
230 | struct swap_info_struct *sis = swap_info[type]; | |
231 | ||
232 | VM_BUG_ON(!frontswap_ops); | |
233 | VM_BUG_ON(sis == NULL); | |
234 | ||
235 | if (!__frontswap_test(sis, offset)) | |
236 | return; | |
237 | ||
238 | frontswap_ops->invalidate_page(type, offset); | |
239 | __frontswap_clear(sis, offset); | |
240 | inc_frontswap_invalidates(); | |
241 | } | |
242 | ||
243 | /* | |
244 | * Invalidate all data from frontswap associated with all offsets for the | |
245 | * specified swaptype. | |
246 | */ | |
247 | void __frontswap_invalidate_area(unsigned type) | |
248 | { | |
249 | struct swap_info_struct *sis = swap_info[type]; | |
250 | ||
251 | VM_BUG_ON(!frontswap_ops); | |
252 | VM_BUG_ON(sis == NULL); | |
253 | ||
254 | if (sis->frontswap_map == NULL) | |
255 | return; | |
256 | ||
257 | frontswap_ops->invalidate_area(type); | |
258 | atomic_set(&sis->frontswap_pages, 0); | |
259 | bitmap_zero(sis->frontswap_map, sis->max); | |
260 | } | |
261 | ||
262 | static int __init init_frontswap(void) | |
263 | { | |
264 | #ifdef CONFIG_DEBUG_FS | |
265 | struct dentry *root = debugfs_create_dir("frontswap", NULL); | |
266 | if (root == NULL) | |
267 | return -ENXIO; | |
268 | debugfs_create_u64("loads", 0444, root, &frontswap_loads); | |
269 | debugfs_create_u64("succ_stores", 0444, root, &frontswap_succ_stores); | |
270 | debugfs_create_u64("failed_stores", 0444, root, | |
271 | &frontswap_failed_stores); | |
272 | debugfs_create_u64("invalidates", 0444, root, &frontswap_invalidates); | |
273 | #endif | |
274 | return 0; | |
275 | } | |
276 | ||
277 | module_init(init_frontswap); |