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
  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 }