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1 | /* | |
2 | * CPU thread main loop - common bits for user and system mode emulation | |
3 | * | |
4 | * Copyright (c) 2003-2005 Fabrice Bellard | |
5 | * | |
6 | * This library is free software; you can redistribute it and/or | |
7 | * modify it under the terms of the GNU Lesser General Public | |
8 | * License as published by the Free Software Foundation; either | |
9 | * version 2.1 of the License, or (at your option) any later version. | |
10 | * | |
11 | * This library is distributed in the hope that it will be useful, | |
12 | * but WITHOUT ANY WARRANTY; without even the implied warranty of | |
13 | * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU | |
14 | * Lesser General Public License for more details. | |
15 | * | |
16 | * You should have received a copy of the GNU Lesser General Public | |
17 | * License along with this library; if not, see <http://www.gnu.org/licenses/>. | |
18 | */ | |
19 | ||
20 | #include "qemu/osdep.h" | |
21 | #include "qemu/main-loop.h" | |
22 | #include "exec/cpu-common.h" | |
23 | #include "hw/core/cpu.h" | |
24 | #include "sysemu/cpus.h" | |
25 | #include "qemu/lockable.h" | |
26 | ||
27 | static QemuMutex qemu_cpu_list_lock; | |
28 | static QemuCond exclusive_cond; | |
29 | static QemuCond exclusive_resume; | |
30 | static QemuCond qemu_work_cond; | |
31 | ||
32 | /* >= 1 if a thread is inside start_exclusive/end_exclusive. Written | |
33 | * under qemu_cpu_list_lock, read with atomic operations. | |
34 | */ | |
35 | static int pending_cpus; | |
36 | ||
37 | void qemu_init_cpu_list(void) | |
38 | { | |
39 | /* This is needed because qemu_init_cpu_list is also called by the | |
40 | * child process in a fork. */ | |
41 | pending_cpus = 0; | |
42 | ||
43 | qemu_mutex_init(&qemu_cpu_list_lock); | |
44 | qemu_cond_init(&exclusive_cond); | |
45 | qemu_cond_init(&exclusive_resume); | |
46 | qemu_cond_init(&qemu_work_cond); | |
47 | } | |
48 | ||
49 | void cpu_list_lock(void) | |
50 | { | |
51 | qemu_mutex_lock(&qemu_cpu_list_lock); | |
52 | } | |
53 | ||
54 | void cpu_list_unlock(void) | |
55 | { | |
56 | qemu_mutex_unlock(&qemu_cpu_list_lock); | |
57 | } | |
58 | ||
59 | static bool cpu_index_auto_assigned; | |
60 | ||
61 | static int cpu_get_free_index(void) | |
62 | { | |
63 | CPUState *some_cpu; | |
64 | int max_cpu_index = 0; | |
65 | ||
66 | cpu_index_auto_assigned = true; | |
67 | CPU_FOREACH(some_cpu) { | |
68 | if (some_cpu->cpu_index >= max_cpu_index) { | |
69 | max_cpu_index = some_cpu->cpu_index + 1; | |
70 | } | |
71 | } | |
72 | return max_cpu_index; | |
73 | } | |
74 | ||
75 | CPUTailQ cpus = QTAILQ_HEAD_INITIALIZER(cpus); | |
76 | static unsigned int cpu_list_generation_id; | |
77 | ||
78 | unsigned int cpu_list_generation_id_get(void) | |
79 | { | |
80 | return cpu_list_generation_id; | |
81 | } | |
82 | ||
83 | void cpu_list_add(CPUState *cpu) | |
84 | { | |
85 | QEMU_LOCK_GUARD(&qemu_cpu_list_lock); | |
86 | if (cpu->cpu_index == UNASSIGNED_CPU_INDEX) { | |
87 | cpu->cpu_index = cpu_get_free_index(); | |
88 | assert(cpu->cpu_index != UNASSIGNED_CPU_INDEX); | |
89 | } else { | |
90 | assert(!cpu_index_auto_assigned); | |
91 | } | |
92 | QTAILQ_INSERT_TAIL_RCU(&cpus, cpu, node); | |
93 | cpu_list_generation_id++; | |
94 | } | |
95 | ||
96 | void cpu_list_remove(CPUState *cpu) | |
97 | { | |
98 | QEMU_LOCK_GUARD(&qemu_cpu_list_lock); | |
99 | if (!QTAILQ_IN_USE(cpu, node)) { | |
100 | /* there is nothing to undo since cpu_exec_init() hasn't been called */ | |
101 | return; | |
102 | } | |
103 | ||
104 | QTAILQ_REMOVE_RCU(&cpus, cpu, node); | |
105 | cpu->cpu_index = UNASSIGNED_CPU_INDEX; | |
106 | cpu_list_generation_id++; | |
107 | } | |
108 | ||
109 | CPUState *qemu_get_cpu(int index) | |
110 | { | |
111 | CPUState *cpu; | |
112 | ||
113 | CPU_FOREACH(cpu) { | |
114 | if (cpu->cpu_index == index) { | |
115 | return cpu; | |
116 | } | |
117 | } | |
118 | ||
119 | return NULL; | |
120 | } | |
121 | ||
122 | /* current CPU in the current thread. It is only valid inside cpu_exec() */ | |
123 | __thread CPUState *current_cpu; | |
124 | ||
125 | struct qemu_work_item { | |
126 | QSIMPLEQ_ENTRY(qemu_work_item) node; | |
127 | run_on_cpu_func func; | |
128 | run_on_cpu_data data; | |
129 | bool free, exclusive, done; | |
130 | }; | |
131 | ||
132 | static void queue_work_on_cpu(CPUState *cpu, struct qemu_work_item *wi) | |
133 | { | |
134 | qemu_mutex_lock(&cpu->work_mutex); | |
135 | QSIMPLEQ_INSERT_TAIL(&cpu->work_list, wi, node); | |
136 | wi->done = false; | |
137 | qemu_mutex_unlock(&cpu->work_mutex); | |
138 | ||
139 | qemu_cpu_kick(cpu); | |
140 | } | |
141 | ||
142 | void do_run_on_cpu(CPUState *cpu, run_on_cpu_func func, run_on_cpu_data data, | |
143 | QemuMutex *mutex) | |
144 | { | |
145 | struct qemu_work_item wi; | |
146 | ||
147 | if (qemu_cpu_is_self(cpu)) { | |
148 | func(cpu, data); | |
149 | return; | |
150 | } | |
151 | ||
152 | wi.func = func; | |
153 | wi.data = data; | |
154 | wi.done = false; | |
155 | wi.free = false; | |
156 | wi.exclusive = false; | |
157 | ||
158 | queue_work_on_cpu(cpu, &wi); | |
159 | while (!qatomic_mb_read(&wi.done)) { | |
160 | CPUState *self_cpu = current_cpu; | |
161 | ||
162 | qemu_cond_wait(&qemu_work_cond, mutex); | |
163 | current_cpu = self_cpu; | |
164 | } | |
165 | } | |
166 | ||
167 | void async_run_on_cpu(CPUState *cpu, run_on_cpu_func func, run_on_cpu_data data) | |
168 | { | |
169 | struct qemu_work_item *wi; | |
170 | ||
171 | wi = g_new0(struct qemu_work_item, 1); | |
172 | wi->func = func; | |
173 | wi->data = data; | |
174 | wi->free = true; | |
175 | ||
176 | queue_work_on_cpu(cpu, wi); | |
177 | } | |
178 | ||
179 | /* Wait for pending exclusive operations to complete. The CPU list lock | |
180 | must be held. */ | |
181 | static inline void exclusive_idle(void) | |
182 | { | |
183 | while (pending_cpus) { | |
184 | qemu_cond_wait(&exclusive_resume, &qemu_cpu_list_lock); | |
185 | } | |
186 | } | |
187 | ||
188 | /* Start an exclusive operation. | |
189 | Must only be called from outside cpu_exec. */ | |
190 | void start_exclusive(void) | |
191 | { | |
192 | CPUState *other_cpu; | |
193 | int running_cpus; | |
194 | ||
195 | qemu_mutex_lock(&qemu_cpu_list_lock); | |
196 | exclusive_idle(); | |
197 | ||
198 | /* Make all other cpus stop executing. */ | |
199 | qatomic_set(&pending_cpus, 1); | |
200 | ||
201 | /* Write pending_cpus before reading other_cpu->running. */ | |
202 | smp_mb(); | |
203 | running_cpus = 0; | |
204 | CPU_FOREACH(other_cpu) { | |
205 | if (qatomic_read(&other_cpu->running)) { | |
206 | other_cpu->has_waiter = true; | |
207 | running_cpus++; | |
208 | qemu_cpu_kick(other_cpu); | |
209 | } | |
210 | } | |
211 | ||
212 | qatomic_set(&pending_cpus, running_cpus + 1); | |
213 | while (pending_cpus > 1) { | |
214 | qemu_cond_wait(&exclusive_cond, &qemu_cpu_list_lock); | |
215 | } | |
216 | ||
217 | /* Can release mutex, no one will enter another exclusive | |
218 | * section until end_exclusive resets pending_cpus to 0. | |
219 | */ | |
220 | qemu_mutex_unlock(&qemu_cpu_list_lock); | |
221 | ||
222 | current_cpu->in_exclusive_context = true; | |
223 | } | |
224 | ||
225 | /* Finish an exclusive operation. */ | |
226 | void end_exclusive(void) | |
227 | { | |
228 | current_cpu->in_exclusive_context = false; | |
229 | ||
230 | qemu_mutex_lock(&qemu_cpu_list_lock); | |
231 | qatomic_set(&pending_cpus, 0); | |
232 | qemu_cond_broadcast(&exclusive_resume); | |
233 | qemu_mutex_unlock(&qemu_cpu_list_lock); | |
234 | } | |
235 | ||
236 | /* Wait for exclusive ops to finish, and begin cpu execution. */ | |
237 | void cpu_exec_start(CPUState *cpu) | |
238 | { | |
239 | qatomic_set(&cpu->running, true); | |
240 | ||
241 | /* Write cpu->running before reading pending_cpus. */ | |
242 | smp_mb(); | |
243 | ||
244 | /* 1. start_exclusive saw cpu->running == true and pending_cpus >= 1. | |
245 | * After taking the lock we'll see cpu->has_waiter == true and run---not | |
246 | * for long because start_exclusive kicked us. cpu_exec_end will | |
247 | * decrement pending_cpus and signal the waiter. | |
248 | * | |
249 | * 2. start_exclusive saw cpu->running == false but pending_cpus >= 1. | |
250 | * This includes the case when an exclusive item is running now. | |
251 | * Then we'll see cpu->has_waiter == false and wait for the item to | |
252 | * complete. | |
253 | * | |
254 | * 3. pending_cpus == 0. Then start_exclusive is definitely going to | |
255 | * see cpu->running == true, and it will kick the CPU. | |
256 | */ | |
257 | if (unlikely(qatomic_read(&pending_cpus))) { | |
258 | QEMU_LOCK_GUARD(&qemu_cpu_list_lock); | |
259 | if (!cpu->has_waiter) { | |
260 | /* Not counted in pending_cpus, let the exclusive item | |
261 | * run. Since we have the lock, just set cpu->running to true | |
262 | * while holding it; no need to check pending_cpus again. | |
263 | */ | |
264 | qatomic_set(&cpu->running, false); | |
265 | exclusive_idle(); | |
266 | /* Now pending_cpus is zero. */ | |
267 | qatomic_set(&cpu->running, true); | |
268 | } else { | |
269 | /* Counted in pending_cpus, go ahead and release the | |
270 | * waiter at cpu_exec_end. | |
271 | */ | |
272 | } | |
273 | } | |
274 | } | |
275 | ||
276 | /* Mark cpu as not executing, and release pending exclusive ops. */ | |
277 | void cpu_exec_end(CPUState *cpu) | |
278 | { | |
279 | qatomic_set(&cpu->running, false); | |
280 | ||
281 | /* Write cpu->running before reading pending_cpus. */ | |
282 | smp_mb(); | |
283 | ||
284 | /* 1. start_exclusive saw cpu->running == true. Then it will increment | |
285 | * pending_cpus and wait for exclusive_cond. After taking the lock | |
286 | * we'll see cpu->has_waiter == true. | |
287 | * | |
288 | * 2. start_exclusive saw cpu->running == false but here pending_cpus >= 1. | |
289 | * This includes the case when an exclusive item started after setting | |
290 | * cpu->running to false and before we read pending_cpus. Then we'll see | |
291 | * cpu->has_waiter == false and not touch pending_cpus. The next call to | |
292 | * cpu_exec_start will run exclusive_idle if still necessary, thus waiting | |
293 | * for the item to complete. | |
294 | * | |
295 | * 3. pending_cpus == 0. Then start_exclusive is definitely going to | |
296 | * see cpu->running == false, and it can ignore this CPU until the | |
297 | * next cpu_exec_start. | |
298 | */ | |
299 | if (unlikely(qatomic_read(&pending_cpus))) { | |
300 | QEMU_LOCK_GUARD(&qemu_cpu_list_lock); | |
301 | if (cpu->has_waiter) { | |
302 | cpu->has_waiter = false; | |
303 | qatomic_set(&pending_cpus, pending_cpus - 1); | |
304 | if (pending_cpus == 1) { | |
305 | qemu_cond_signal(&exclusive_cond); | |
306 | } | |
307 | } | |
308 | } | |
309 | } | |
310 | ||
311 | void async_safe_run_on_cpu(CPUState *cpu, run_on_cpu_func func, | |
312 | run_on_cpu_data data) | |
313 | { | |
314 | struct qemu_work_item *wi; | |
315 | ||
316 | wi = g_new0(struct qemu_work_item, 1); | |
317 | wi->func = func; | |
318 | wi->data = data; | |
319 | wi->free = true; | |
320 | wi->exclusive = true; | |
321 | ||
322 | queue_work_on_cpu(cpu, wi); | |
323 | } | |
324 | ||
325 | void process_queued_cpu_work(CPUState *cpu) | |
326 | { | |
327 | struct qemu_work_item *wi; | |
328 | ||
329 | qemu_mutex_lock(&cpu->work_mutex); | |
330 | if (QSIMPLEQ_EMPTY(&cpu->work_list)) { | |
331 | qemu_mutex_unlock(&cpu->work_mutex); | |
332 | return; | |
333 | } | |
334 | while (!QSIMPLEQ_EMPTY(&cpu->work_list)) { | |
335 | wi = QSIMPLEQ_FIRST(&cpu->work_list); | |
336 | QSIMPLEQ_REMOVE_HEAD(&cpu->work_list, node); | |
337 | qemu_mutex_unlock(&cpu->work_mutex); | |
338 | if (wi->exclusive) { | |
339 | /* Running work items outside the BQL avoids the following deadlock: | |
340 | * 1) start_exclusive() is called with the BQL taken while another | |
341 | * CPU is running; 2) cpu_exec in the other CPU tries to takes the | |
342 | * BQL, so it goes to sleep; start_exclusive() is sleeping too, so | |
343 | * neither CPU can proceed. | |
344 | */ | |
345 | qemu_mutex_unlock_iothread(); | |
346 | start_exclusive(); | |
347 | wi->func(cpu, wi->data); | |
348 | end_exclusive(); | |
349 | qemu_mutex_lock_iothread(); | |
350 | } else { | |
351 | wi->func(cpu, wi->data); | |
352 | } | |
353 | qemu_mutex_lock(&cpu->work_mutex); | |
354 | if (wi->free) { | |
355 | g_free(wi); | |
356 | } else { | |
357 | qatomic_mb_set(&wi->done, true); | |
358 | } | |
359 | } | |
360 | qemu_mutex_unlock(&cpu->work_mutex); | |
361 | qemu_cond_broadcast(&qemu_work_cond); | |
362 | } |