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 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 | |
26 | static QemuMutex qemu_cpu_list_lock; |
27 | static QemuCond exclusive_cond; |
28 | static QemuCond exclusive_resume; |
29 | static QemuCond qemu_work_cond; |
30 | |
31 | /* >= 1 if a thread is inside start_exclusive/end_exclusive. Written |
32 | * under qemu_cpu_list_lock, read with atomic operations. |
33 | */ |
34 | static int pending_cpus; |
35 | |
36 | void qemu_init_cpu_list(void) |
37 | { |
38 | /* This is needed because qemu_init_cpu_list is also called by the |
39 | * child process in a fork. */ |
40 | pending_cpus = 0; |
41 | |
42 | qemu_mutex_init(&qemu_cpu_list_lock); |
43 | qemu_cond_init(&exclusive_cond); |
44 | qemu_cond_init(&exclusive_resume); |
45 | qemu_cond_init(&qemu_work_cond); |
46 | } |
47 | |
48 | void cpu_list_lock(void) |
49 | { |
50 | qemu_mutex_lock(&qemu_cpu_list_lock); |
51 | } |
52 | |
53 | void cpu_list_unlock(void) |
54 | { |
55 | qemu_mutex_unlock(&qemu_cpu_list_lock); |
56 | } |
57 | |
58 | static bool cpu_index_auto_assigned; |
59 | |
60 | static int cpu_get_free_index(void) |
61 | { |
62 | CPUState *some_cpu; |
63 | int cpu_index = 0; |
64 | |
65 | cpu_index_auto_assigned = true; |
66 | CPU_FOREACH(some_cpu) { |
67 | cpu_index++; |
68 | } |
69 | return cpu_index; |
70 | } |
71 | |
72 | void cpu_list_add(CPUState *cpu) |
73 | { |
74 | qemu_mutex_lock(&qemu_cpu_list_lock); |
75 | if (cpu->cpu_index == UNASSIGNED_CPU_INDEX) { |
76 | cpu->cpu_index = cpu_get_free_index(); |
77 | assert(cpu->cpu_index != UNASSIGNED_CPU_INDEX); |
78 | } else { |
79 | assert(!cpu_index_auto_assigned); |
80 | } |
81 | QTAILQ_INSERT_TAIL_RCU(&cpus, cpu, node); |
82 | qemu_mutex_unlock(&qemu_cpu_list_lock); |
83 | } |
84 | |
85 | void cpu_list_remove(CPUState *cpu) |
86 | { |
87 | qemu_mutex_lock(&qemu_cpu_list_lock); |
88 | if (!QTAILQ_IN_USE(cpu, node)) { |
89 | /* there is nothing to undo since cpu_exec_init() hasn't been called */ |
90 | qemu_mutex_unlock(&qemu_cpu_list_lock); |
91 | return; |
92 | } |
93 | |
94 | assert(!(cpu_index_auto_assigned && cpu != QTAILQ_LAST(&cpus))); |
95 | |
96 | QTAILQ_REMOVE_RCU(&cpus, cpu, node); |
97 | cpu->cpu_index = UNASSIGNED_CPU_INDEX; |
98 | qemu_mutex_unlock(&qemu_cpu_list_lock); |
99 | } |
100 | |
101 | struct qemu_work_item { |
102 | struct qemu_work_item *next; |
103 | run_on_cpu_func func; |
104 | run_on_cpu_data data; |
105 | bool free, exclusive, done; |
106 | }; |
107 | |
108 | static void queue_work_on_cpu(CPUState *cpu, struct qemu_work_item *wi) |
109 | { |
110 | qemu_mutex_lock(&cpu->work_mutex); |
111 | if (cpu->queued_work_first == NULL) { |
112 | cpu->queued_work_first = wi; |
113 | } else { |
114 | cpu->queued_work_last->next = wi; |
115 | } |
116 | cpu->queued_work_last = wi; |
117 | wi->next = NULL; |
118 | wi->done = false; |
119 | qemu_mutex_unlock(&cpu->work_mutex); |
120 | |
121 | qemu_cpu_kick(cpu); |
122 | } |
123 | |
124 | void do_run_on_cpu(CPUState *cpu, run_on_cpu_func func, run_on_cpu_data data, |
125 | QemuMutex *mutex) |
126 | { |
127 | struct qemu_work_item wi; |
128 | |
129 | if (qemu_cpu_is_self(cpu)) { |
130 | func(cpu, data); |
131 | return; |
132 | } |
133 | |
134 | wi.func = func; |
135 | wi.data = data; |
136 | wi.done = false; |
137 | wi.free = false; |
138 | wi.exclusive = false; |
139 | |
140 | queue_work_on_cpu(cpu, &wi); |
141 | while (!atomic_mb_read(&wi.done)) { |
142 | CPUState *self_cpu = current_cpu; |
143 | |
144 | qemu_cond_wait(&qemu_work_cond, mutex); |
145 | current_cpu = self_cpu; |
146 | } |
147 | } |
148 | |
149 | void async_run_on_cpu(CPUState *cpu, run_on_cpu_func func, run_on_cpu_data data) |
150 | { |
151 | struct qemu_work_item *wi; |
152 | |
153 | wi = g_malloc0(sizeof(struct qemu_work_item)); |
154 | wi->func = func; |
155 | wi->data = data; |
156 | wi->free = true; |
157 | |
158 | queue_work_on_cpu(cpu, wi); |
159 | } |
160 | |
161 | /* Wait for pending exclusive operations to complete. The CPU list lock |
162 | must be held. */ |
163 | static inline void exclusive_idle(void) |
164 | { |
165 | while (pending_cpus) { |
166 | qemu_cond_wait(&exclusive_resume, &qemu_cpu_list_lock); |
167 | } |
168 | } |
169 | |
170 | /* Start an exclusive operation. |
171 | Must only be called from outside cpu_exec. */ |
172 | void start_exclusive(void) |
173 | { |
174 | CPUState *other_cpu; |
175 | int running_cpus; |
176 | |
177 | qemu_mutex_lock(&qemu_cpu_list_lock); |
178 | exclusive_idle(); |
179 | |
180 | /* Make all other cpus stop executing. */ |
181 | atomic_set(&pending_cpus, 1); |
182 | |
183 | /* Write pending_cpus before reading other_cpu->running. */ |
184 | smp_mb(); |
185 | running_cpus = 0; |
186 | CPU_FOREACH(other_cpu) { |
187 | if (atomic_read(&other_cpu->running)) { |
188 | other_cpu->has_waiter = true; |
189 | running_cpus++; |
190 | qemu_cpu_kick(other_cpu); |
191 | } |
192 | } |
193 | |
194 | atomic_set(&pending_cpus, running_cpus + 1); |
195 | while (pending_cpus > 1) { |
196 | qemu_cond_wait(&exclusive_cond, &qemu_cpu_list_lock); |
197 | } |
198 | |
199 | /* Can release mutex, no one will enter another exclusive |
200 | * section until end_exclusive resets pending_cpus to 0. |
201 | */ |
202 | qemu_mutex_unlock(&qemu_cpu_list_lock); |
203 | } |
204 | |
205 | /* Finish an exclusive operation. */ |
206 | void end_exclusive(void) |
207 | { |
208 | qemu_mutex_lock(&qemu_cpu_list_lock); |
209 | atomic_set(&pending_cpus, 0); |
210 | qemu_cond_broadcast(&exclusive_resume); |
211 | qemu_mutex_unlock(&qemu_cpu_list_lock); |
212 | } |
213 | |
214 | /* Wait for exclusive ops to finish, and begin cpu execution. */ |
215 | void cpu_exec_start(CPUState *cpu) |
216 | { |
217 | atomic_set(&cpu->running, true); |
218 | |
219 | /* Write cpu->running before reading pending_cpus. */ |
220 | smp_mb(); |
221 | |
222 | /* 1. start_exclusive saw cpu->running == true and pending_cpus >= 1. |
223 | * After taking the lock we'll see cpu->has_waiter == true and run---not |
224 | * for long because start_exclusive kicked us. cpu_exec_end will |
225 | * decrement pending_cpus and signal the waiter. |
226 | * |
227 | * 2. start_exclusive saw cpu->running == false but pending_cpus >= 1. |
228 | * This includes the case when an exclusive item is running now. |
229 | * Then we'll see cpu->has_waiter == false and wait for the item to |
230 | * complete. |
231 | * |
232 | * 3. pending_cpus == 0. Then start_exclusive is definitely going to |
233 | * see cpu->running == true, and it will kick the CPU. |
234 | */ |
235 | if (unlikely(atomic_read(&pending_cpus))) { |
236 | qemu_mutex_lock(&qemu_cpu_list_lock); |
237 | if (!cpu->has_waiter) { |
238 | /* Not counted in pending_cpus, let the exclusive item |
239 | * run. Since we have the lock, just set cpu->running to true |
240 | * while holding it; no need to check pending_cpus again. |
241 | */ |
242 | atomic_set(&cpu->running, false); |
243 | exclusive_idle(); |
244 | /* Now pending_cpus is zero. */ |
245 | atomic_set(&cpu->running, true); |
246 | } else { |
247 | /* Counted in pending_cpus, go ahead and release the |
248 | * waiter at cpu_exec_end. |
249 | */ |
250 | } |
251 | qemu_mutex_unlock(&qemu_cpu_list_lock); |
252 | } |
253 | } |
254 | |
255 | /* Mark cpu as not executing, and release pending exclusive ops. */ |
256 | void cpu_exec_end(CPUState *cpu) |
257 | { |
258 | atomic_set(&cpu->running, false); |
259 | |
260 | /* Write cpu->running before reading pending_cpus. */ |
261 | smp_mb(); |
262 | |
263 | /* 1. start_exclusive saw cpu->running == true. Then it will increment |
264 | * pending_cpus and wait for exclusive_cond. After taking the lock |
265 | * we'll see cpu->has_waiter == true. |
266 | * |
267 | * 2. start_exclusive saw cpu->running == false but here pending_cpus >= 1. |
268 | * This includes the case when an exclusive item started after setting |
269 | * cpu->running to false and before we read pending_cpus. Then we'll see |
270 | * cpu->has_waiter == false and not touch pending_cpus. The next call to |
271 | * cpu_exec_start will run exclusive_idle if still necessary, thus waiting |
272 | * for the item to complete. |
273 | * |
274 | * 3. pending_cpus == 0. Then start_exclusive is definitely going to |
275 | * see cpu->running == false, and it can ignore this CPU until the |
276 | * next cpu_exec_start. |
277 | */ |
278 | if (unlikely(atomic_read(&pending_cpus))) { |
279 | qemu_mutex_lock(&qemu_cpu_list_lock); |
280 | if (cpu->has_waiter) { |
281 | cpu->has_waiter = false; |
282 | atomic_set(&pending_cpus, pending_cpus - 1); |
283 | if (pending_cpus == 1) { |
284 | qemu_cond_signal(&exclusive_cond); |
285 | } |
286 | } |
287 | qemu_mutex_unlock(&qemu_cpu_list_lock); |
288 | } |
289 | } |
290 | |
291 | void async_safe_run_on_cpu(CPUState *cpu, run_on_cpu_func func, |
292 | run_on_cpu_data data) |
293 | { |
294 | struct qemu_work_item *wi; |
295 | |
296 | wi = g_malloc0(sizeof(struct qemu_work_item)); |
297 | wi->func = func; |
298 | wi->data = data; |
299 | wi->free = true; |
300 | wi->exclusive = true; |
301 | |
302 | queue_work_on_cpu(cpu, wi); |
303 | } |
304 | |
305 | void process_queued_cpu_work(CPUState *cpu) |
306 | { |
307 | struct qemu_work_item *wi; |
308 | |
309 | if (cpu->queued_work_first == NULL) { |
310 | return; |
311 | } |
312 | |
313 | qemu_mutex_lock(&cpu->work_mutex); |
314 | while (cpu->queued_work_first != NULL) { |
315 | wi = cpu->queued_work_first; |
316 | cpu->queued_work_first = wi->next; |
317 | if (!cpu->queued_work_first) { |
318 | cpu->queued_work_last = NULL; |
319 | } |
320 | qemu_mutex_unlock(&cpu->work_mutex); |
321 | if (wi->exclusive) { |
322 | /* Running work items outside the BQL avoids the following deadlock: |
323 | * 1) start_exclusive() is called with the BQL taken while another |
324 | * CPU is running; 2) cpu_exec in the other CPU tries to takes the |
325 | * BQL, so it goes to sleep; start_exclusive() is sleeping too, so |
326 | * neither CPU can proceed. |
327 | */ |
328 | qemu_mutex_unlock_iothread(); |
329 | start_exclusive(); |
330 | wi->func(cpu, wi->data); |
331 | end_exclusive(); |
332 | qemu_mutex_lock_iothread(); |
333 | } else { |
334 | wi->func(cpu, wi->data); |
335 | } |
336 | qemu_mutex_lock(&cpu->work_mutex); |
337 | if (wi->free) { |
338 | g_free(wi); |
339 | } else { |
340 | atomic_mb_set(&wi->done, true); |
341 | } |
342 | } |
343 | qemu_mutex_unlock(&cpu->work_mutex); |
344 | qemu_cond_broadcast(&qemu_work_cond); |
345 | } |
346 | |