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