Update version for v7.1.0-rc2 release
[qemu.git] / cpus-common.c
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 }