jump-label: export jump_label_inc/jump_label_dec
[linux-2.6.git] / kernel / jump_label.c
1 /*
2  * jump label support
3  *
4  * Copyright (C) 2009 Jason Baron <jbaron@redhat.com>
5  * Copyright (C) 2011 Peter Zijlstra <pzijlstr@redhat.com>
6  *
7  */
8 #include <linux/memory.h>
9 #include <linux/uaccess.h>
10 #include <linux/module.h>
11 #include <linux/list.h>
12 #include <linux/slab.h>
13 #include <linux/sort.h>
14 #include <linux/err.h>
15 #include <linux/jump_label.h>
16
17 #ifdef HAVE_JUMP_LABEL
18
19 /* mutex to protect coming/going of the the jump_label table */
20 static DEFINE_MUTEX(jump_label_mutex);
21
22 void jump_label_lock(void)
23 {
24         mutex_lock(&jump_label_mutex);
25 }
26
27 void jump_label_unlock(void)
28 {
29         mutex_unlock(&jump_label_mutex);
30 }
31
32 bool jump_label_enabled(struct jump_label_key *key)
33 {
34         return !!atomic_read(&key->enabled);
35 }
36
37 static int jump_label_cmp(const void *a, const void *b)
38 {
39         const struct jump_entry *jea = a;
40         const struct jump_entry *jeb = b;
41
42         if (jea->key < jeb->key)
43                 return -1;
44
45         if (jea->key > jeb->key)
46                 return 1;
47
48         return 0;
49 }
50
51 static void
52 jump_label_sort_entries(struct jump_entry *start, struct jump_entry *stop)
53 {
54         unsigned long size;
55
56         size = (((unsigned long)stop - (unsigned long)start)
57                                         / sizeof(struct jump_entry));
58         sort(start, size, sizeof(struct jump_entry), jump_label_cmp, NULL);
59 }
60
61 static void jump_label_update(struct jump_label_key *key, int enable);
62
63 void jump_label_inc(struct jump_label_key *key)
64 {
65         if (atomic_inc_not_zero(&key->enabled))
66                 return;
67
68         jump_label_lock();
69         if (atomic_read(&key->enabled) == 0)
70                 jump_label_update(key, JUMP_LABEL_ENABLE);
71         atomic_inc(&key->enabled);
72         jump_label_unlock();
73 }
74 EXPORT_SYMBOL_GPL(jump_label_inc);
75
76 void jump_label_dec(struct jump_label_key *key)
77 {
78         if (!atomic_dec_and_mutex_lock(&key->enabled, &jump_label_mutex))
79                 return;
80
81         jump_label_update(key, JUMP_LABEL_DISABLE);
82         jump_label_unlock();
83 }
84 EXPORT_SYMBOL_GPL(jump_label_dec);
85
86 static int addr_conflict(struct jump_entry *entry, void *start, void *end)
87 {
88         if (entry->code <= (unsigned long)end &&
89                 entry->code + JUMP_LABEL_NOP_SIZE > (unsigned long)start)
90                 return 1;
91
92         return 0;
93 }
94
95 static int __jump_label_text_reserved(struct jump_entry *iter_start,
96                 struct jump_entry *iter_stop, void *start, void *end)
97 {
98         struct jump_entry *iter;
99
100         iter = iter_start;
101         while (iter < iter_stop) {
102                 if (addr_conflict(iter, start, end))
103                         return 1;
104                 iter++;
105         }
106
107         return 0;
108 }
109
110 /* 
111  * Update code which is definitely not currently executing.
112  * Architectures which need heavyweight synchronization to modify
113  * running code can override this to make the non-live update case
114  * cheaper.
115  */
116 void __weak arch_jump_label_transform_static(struct jump_entry *entry,
117                                             enum jump_label_type type)
118 {
119         arch_jump_label_transform(entry, type); 
120 }
121
122 static void __jump_label_update(struct jump_label_key *key,
123                                 struct jump_entry *entry,
124                                 struct jump_entry *stop, int enable)
125 {
126         for (; (entry < stop) &&
127               (entry->key == (jump_label_t)(unsigned long)key);
128               entry++) {
129                 /*
130                  * entry->code set to 0 invalidates module init text sections
131                  * kernel_text_address() verifies we are not in core kernel
132                  * init code, see jump_label_invalidate_module_init().
133                  */
134                 if (entry->code && kernel_text_address(entry->code))
135                         arch_jump_label_transform(entry, enable);
136         }
137 }
138
139 void __init jump_label_init(void)
140 {
141         struct jump_entry *iter_start = __start___jump_table;
142         struct jump_entry *iter_stop = __stop___jump_table;
143         struct jump_label_key *key = NULL;
144         struct jump_entry *iter;
145
146         jump_label_lock();
147         jump_label_sort_entries(iter_start, iter_stop);
148
149         for (iter = iter_start; iter < iter_stop; iter++) {
150                 struct jump_label_key *iterk;
151
152                 iterk = (struct jump_label_key *)(unsigned long)iter->key;
153                 arch_jump_label_transform_static(iter, jump_label_enabled(iterk) ?
154                                                  JUMP_LABEL_ENABLE : JUMP_LABEL_DISABLE);
155                 if (iterk == key)
156                         continue;
157
158                 key = iterk;
159                 key->entries = iter;
160 #ifdef CONFIG_MODULES
161                 key->next = NULL;
162 #endif
163         }
164         jump_label_unlock();
165 }
166
167 #ifdef CONFIG_MODULES
168
169 struct jump_label_mod {
170         struct jump_label_mod *next;
171         struct jump_entry *entries;
172         struct module *mod;
173 };
174
175 static int __jump_label_mod_text_reserved(void *start, void *end)
176 {
177         struct module *mod;
178
179         mod = __module_text_address((unsigned long)start);
180         if (!mod)
181                 return 0;
182
183         WARN_ON_ONCE(__module_text_address((unsigned long)end) != mod);
184
185         return __jump_label_text_reserved(mod->jump_entries,
186                                 mod->jump_entries + mod->num_jump_entries,
187                                 start, end);
188 }
189
190 static void __jump_label_mod_update(struct jump_label_key *key, int enable)
191 {
192         struct jump_label_mod *mod = key->next;
193
194         while (mod) {
195                 struct module *m = mod->mod;
196
197                 __jump_label_update(key, mod->entries,
198                                     m->jump_entries + m->num_jump_entries,
199                                     enable);
200                 mod = mod->next;
201         }
202 }
203
204 /***
205  * apply_jump_label_nops - patch module jump labels with arch_get_jump_label_nop()
206  * @mod: module to patch
207  *
208  * Allow for run-time selection of the optimal nops. Before the module
209  * loads patch these with arch_get_jump_label_nop(), which is specified by
210  * the arch specific jump label code.
211  */
212 void jump_label_apply_nops(struct module *mod)
213 {
214         struct jump_entry *iter_start = mod->jump_entries;
215         struct jump_entry *iter_stop = iter_start + mod->num_jump_entries;
216         struct jump_entry *iter;
217
218         /* if the module doesn't have jump label entries, just return */
219         if (iter_start == iter_stop)
220                 return;
221
222         for (iter = iter_start; iter < iter_stop; iter++)
223                 arch_jump_label_transform_static(iter, JUMP_LABEL_DISABLE);
224 }
225
226 static int jump_label_add_module(struct module *mod)
227 {
228         struct jump_entry *iter_start = mod->jump_entries;
229         struct jump_entry *iter_stop = iter_start + mod->num_jump_entries;
230         struct jump_entry *iter;
231         struct jump_label_key *key = NULL;
232         struct jump_label_mod *jlm;
233
234         /* if the module doesn't have jump label entries, just return */
235         if (iter_start == iter_stop)
236                 return 0;
237
238         jump_label_sort_entries(iter_start, iter_stop);
239
240         for (iter = iter_start; iter < iter_stop; iter++) {
241                 if (iter->key == (jump_label_t)(unsigned long)key)
242                         continue;
243
244                 key = (struct jump_label_key *)(unsigned long)iter->key;
245
246                 if (__module_address(iter->key) == mod) {
247                         atomic_set(&key->enabled, 0);
248                         key->entries = iter;
249                         key->next = NULL;
250                         continue;
251                 }
252
253                 jlm = kzalloc(sizeof(struct jump_label_mod), GFP_KERNEL);
254                 if (!jlm)
255                         return -ENOMEM;
256
257                 jlm->mod = mod;
258                 jlm->entries = iter;
259                 jlm->next = key->next;
260                 key->next = jlm;
261
262                 if (jump_label_enabled(key))
263                         __jump_label_update(key, iter, iter_stop,
264                                             JUMP_LABEL_ENABLE);
265         }
266
267         return 0;
268 }
269
270 static void jump_label_del_module(struct module *mod)
271 {
272         struct jump_entry *iter_start = mod->jump_entries;
273         struct jump_entry *iter_stop = iter_start + mod->num_jump_entries;
274         struct jump_entry *iter;
275         struct jump_label_key *key = NULL;
276         struct jump_label_mod *jlm, **prev;
277
278         for (iter = iter_start; iter < iter_stop; iter++) {
279                 if (iter->key == (jump_label_t)(unsigned long)key)
280                         continue;
281
282                 key = (struct jump_label_key *)(unsigned long)iter->key;
283
284                 if (__module_address(iter->key) == mod)
285                         continue;
286
287                 prev = &key->next;
288                 jlm = key->next;
289
290                 while (jlm && jlm->mod != mod) {
291                         prev = &jlm->next;
292                         jlm = jlm->next;
293                 }
294
295                 if (jlm) {
296                         *prev = jlm->next;
297                         kfree(jlm);
298                 }
299         }
300 }
301
302 static void jump_label_invalidate_module_init(struct module *mod)
303 {
304         struct jump_entry *iter_start = mod->jump_entries;
305         struct jump_entry *iter_stop = iter_start + mod->num_jump_entries;
306         struct jump_entry *iter;
307
308         for (iter = iter_start; iter < iter_stop; iter++) {
309                 if (within_module_init(iter->code, mod))
310                         iter->code = 0;
311         }
312 }
313
314 static int
315 jump_label_module_notify(struct notifier_block *self, unsigned long val,
316                          void *data)
317 {
318         struct module *mod = data;
319         int ret = 0;
320
321         switch (val) {
322         case MODULE_STATE_COMING:
323                 jump_label_lock();
324                 ret = jump_label_add_module(mod);
325                 if (ret)
326                         jump_label_del_module(mod);
327                 jump_label_unlock();
328                 break;
329         case MODULE_STATE_GOING:
330                 jump_label_lock();
331                 jump_label_del_module(mod);
332                 jump_label_unlock();
333                 break;
334         case MODULE_STATE_LIVE:
335                 jump_label_lock();
336                 jump_label_invalidate_module_init(mod);
337                 jump_label_unlock();
338                 break;
339         }
340
341         return notifier_from_errno(ret);
342 }
343
344 struct notifier_block jump_label_module_nb = {
345         .notifier_call = jump_label_module_notify,
346         .priority = 1, /* higher than tracepoints */
347 };
348
349 static __init int jump_label_init_module(void)
350 {
351         return register_module_notifier(&jump_label_module_nb);
352 }
353 early_initcall(jump_label_init_module);
354
355 #endif /* CONFIG_MODULES */
356
357 /***
358  * jump_label_text_reserved - check if addr range is reserved
359  * @start: start text addr
360  * @end: end text addr
361  *
362  * checks if the text addr located between @start and @end
363  * overlaps with any of the jump label patch addresses. Code
364  * that wants to modify kernel text should first verify that
365  * it does not overlap with any of the jump label addresses.
366  * Caller must hold jump_label_mutex.
367  *
368  * returns 1 if there is an overlap, 0 otherwise
369  */
370 int jump_label_text_reserved(void *start, void *end)
371 {
372         int ret = __jump_label_text_reserved(__start___jump_table,
373                         __stop___jump_table, start, end);
374
375         if (ret)
376                 return ret;
377
378 #ifdef CONFIG_MODULES
379         ret = __jump_label_mod_text_reserved(start, end);
380 #endif
381         return ret;
382 }
383
384 static void jump_label_update(struct jump_label_key *key, int enable)
385 {
386         struct jump_entry *entry = key->entries, *stop = __stop___jump_table;
387
388 #ifdef CONFIG_MODULES
389         struct module *mod = __module_address((jump_label_t)key);
390
391         __jump_label_mod_update(key, enable);
392
393         if (mod)
394                 stop = mod->jump_entries + mod->num_jump_entries;
395 #endif
396         /* if there are no users, entry can be NULL */
397         if (entry)
398                 __jump_label_update(key, entry, stop, enable);
399 }
400
401 #endif