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 "qom/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 static int pending_cpus;
  32
  33 void qemu_init_cpu_list(void)
  34 {
  35     /* This is needed because qemu_init_cpu_list is also called by the
  36      * child process in a fork.  */
  37     pending_cpus = 0;
  38
  39     qemu_mutex_init(&qemu_cpu_list_lock);
  40     qemu_cond_init(&exclusive_cond);
  41     qemu_cond_init(&exclusive_resume);
  42     qemu_cond_init(&qemu_work_cond);
  43 }
  44
  45 void cpu_list_lock(void)
  46 {
  47     qemu_mutex_lock(&qemu_cpu_list_lock);
  48 }
  49
  50 void cpu_list_unlock(void)
  51 {
  52     qemu_mutex_unlock(&qemu_cpu_list_lock);
  53 }
  54
  55 static bool cpu_index_auto_assigned;
  56
  57 static int cpu_get_free_index(void)
  58 {
  59     CPUState *some_cpu;
  60     int cpu_index = 0;
  61
  62     cpu_index_auto_assigned = true;
  63     CPU_FOREACH(some_cpu) {
  64         cpu_index++;
  65     }
  66     return cpu_index;
  67 }
  68
  69 static void finish_safe_work(CPUState *cpu)
  70 {
  71     cpu_exec_start(cpu);
  72     cpu_exec_end(cpu);
  73 }
  74
  75 void cpu_list_add(CPUState *cpu)
  76 {
  77     qemu_mutex_lock(&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(&cpus, cpu, node);
  85     qemu_mutex_unlock(&qemu_cpu_list_lock);
  86
  87     finish_safe_work(cpu);
  88 }
  89
  90 void cpu_list_remove(CPUState *cpu)
  91 {
  92     qemu_mutex_lock(&qemu_cpu_list_lock);
  93     if (!QTAILQ_IN_USE(cpu, node)) {
  94         /* there is nothing to undo since cpu_exec_init() hasn't been called */
  95         qemu_mutex_unlock(&qemu_cpu_list_lock);
  96         return;
  97     }
  98
  99     assert(!(cpu_index_auto_assigned && cpu != QTAILQ_LAST(&cpus, CPUTailQ)));
 100
 101     QTAILQ_REMOVE(&cpus, cpu, node);
 102     cpu->cpu_index = UNASSIGNED_CPU_INDEX;
 103     qemu_mutex_unlock(&qemu_cpu_list_lock);
 104 }
 105
 106 struct qemu_work_item {
 107     struct qemu_work_item *next;
 108     run_on_cpu_func func;
 109     void *data;
 110     bool free, exclusive, done;
 111 };
 112
 113 static void queue_work_on_cpu(CPUState *cpu, struct qemu_work_item *wi)
 114 {
 115     qemu_mutex_lock(&cpu->work_mutex);
 116     if (cpu->queued_work_first == NULL) {
 117         cpu->queued_work_first = wi;
 118     } else {
 119         cpu->queued_work_last->next = wi;
 120     }
 121     cpu->queued_work_last = wi;
 122     wi->next = NULL;
 123     wi->done = false;
 124     qemu_mutex_unlock(&cpu->work_mutex);
 125
 126     qemu_cpu_kick(cpu);
 127 }
 128
 129 void do_run_on_cpu(CPUState *cpu, run_on_cpu_func func, void *data,
 130                    QemuMutex *mutex)
 131 {
 132     struct qemu_work_item wi;
 133
 134     if (qemu_cpu_is_self(cpu)) {
 135         func(cpu, data);
 136         return;
 137     }
 138
 139     wi.func = func;
 140     wi.data = data;
 141     wi.done = false;
 142     wi.free = false;
 143     wi.exclusive = false;
 144
 145     queue_work_on_cpu(cpu, &wi);
 146     while (!atomic_mb_read(&wi.done)) {
 147         CPUState *self_cpu = current_cpu;
 148
 149         qemu_cond_wait(&qemu_work_cond, mutex);
 150         current_cpu = self_cpu;
 151     }
 152 }
 153
 154 void async_run_on_cpu(CPUState *cpu, run_on_cpu_func func, void *data)
 155 {
 156     struct qemu_work_item *wi;
 157
 158     wi = g_malloc0(sizeof(struct qemu_work_item));
 159     wi->func = func;
 160     wi->data = data;
 161     wi->free = true;
 162
 163     queue_work_on_cpu(cpu, wi);
 164 }
 165
 166 /* Wait for pending exclusive operations to complete.  The CPU list lock
 167    must be held.  */
 168 static inline void exclusive_idle(void)
 169 {
 170     while (pending_cpus) {
 171         qemu_cond_wait(&exclusive_resume, &qemu_cpu_list_lock);
 172     }
 173 }
 174
 175 /* Start an exclusive operation.
 176    Must only be called from outside cpu_exec.  */
 177 void start_exclusive(void)
 178 {
 179     CPUState *other_cpu;
 180
 181     qemu_mutex_lock(&qemu_cpu_list_lock);
 182     exclusive_idle();
 183
 184     /* Make all other cpus stop executing.  */
 185     pending_cpus = 1;
 186     CPU_FOREACH(other_cpu) {
 187         if (other_cpu->running) {
 188             pending_cpus++;
 189             qemu_cpu_kick(other_cpu);
 190         }
 191     }
 192     while (pending_cpus > 1) {
 193         qemu_cond_wait(&exclusive_cond, &qemu_cpu_list_lock);
 194     }
 195
 196     /* Can release mutex, no one will enter another exclusive
 197      * section until end_exclusive resets pending_cpus to 0.
 198      */
 199     qemu_mutex_unlock(&qemu_cpu_list_lock);
 200 }
 201
 202 /* Finish an exclusive operation.  */
 203 void end_exclusive(void)
 204 {
 205     qemu_mutex_lock(&qemu_cpu_list_lock);
 206     pending_cpus = 0;
 207     qemu_cond_broadcast(&exclusive_resume);
 208     qemu_mutex_unlock(&qemu_cpu_list_lock);
 209 }
 210
 211 /* Wait for exclusive ops to finish, and begin cpu execution.  */
 212 void cpu_exec_start(CPUState *cpu)
 213 {
 214     qemu_mutex_lock(&qemu_cpu_list_lock);
 215     exclusive_idle();
 216     cpu->running = true;
 217     qemu_mutex_unlock(&qemu_cpu_list_lock);
 218 }
 219
 220 /* Mark cpu as not executing, and release pending exclusive ops.  */
 221 void cpu_exec_end(CPUState *cpu)
 222 {
 223     qemu_mutex_lock(&qemu_cpu_list_lock);
 224     cpu->running = false;
 225     if (pending_cpus > 1) {
 226         pending_cpus--;
 227         if (pending_cpus == 1) {
 228             qemu_cond_signal(&exclusive_cond);
 229         }
 230     }
 231     qemu_mutex_unlock(&qemu_cpu_list_lock);
 232 }
 233
 234 void async_safe_run_on_cpu(CPUState *cpu, run_on_cpu_func func, void *data)
 235 {
 236     struct qemu_work_item *wi;
 237
 238     wi = g_malloc0(sizeof(struct qemu_work_item));
 239     wi->func = func;
 240     wi->data = data;
 241     wi->free = true;
 242     wi->exclusive = true;
 243
 244     queue_work_on_cpu(cpu, wi);
 245 }
 246
 247 void process_queued_cpu_work(CPUState *cpu)
 248 {
 249     struct qemu_work_item *wi;
 250
 251     if (cpu->queued_work_first == NULL) {
 252         return;
 253     }
 254
 255     qemu_mutex_lock(&cpu->work_mutex);
 256     while (cpu->queued_work_first != NULL) {
 257         wi = cpu->queued_work_first;
 258         cpu->queued_work_first = wi->next;
 259         if (!cpu->queued_work_first) {
 260             cpu->queued_work_last = NULL;
 261         }
 262         qemu_mutex_unlock(&cpu->work_mutex);
 263         if (wi->exclusive) {
 264             /* Running work items outside the BQL avoids the following deadlock:
 265              * 1) start_exclusive() is called with the BQL taken while another
 266              * CPU is running; 2) cpu_exec in the other CPU tries to takes the
 267              * BQL, so it goes to sleep; start_exclusive() is sleeping too, so
 268              * neither CPU can proceed.
 269              */
 270             qemu_mutex_unlock_iothread();
 271             start_exclusive();
 272             wi->func(cpu, wi->data);
 273             end_exclusive();
 274             qemu_mutex_lock_iothread();
 275         } else {
 276             wi->func(cpu, wi->data);
 277         }
 278         qemu_mutex_lock(&cpu->work_mutex);
 279         if (wi->free) {
 280             g_free(wi);
 281         } else {
 282             atomic_mb_set(&wi->done, true);
 283         }
 284     }
 285     qemu_mutex_unlock(&cpu->work_mutex);
 286     qemu_cond_broadcast(&qemu_work_cond);
 287 }