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 /* >= 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 static void finish_safe_work(CPUState *cpu)
  73 {
  74     cpu_exec_start(cpu);
  75     cpu_exec_end(cpu);
  76 }
  77
  78 void cpu_list_add(CPUState *cpu)
  79 {
  80     qemu_mutex_lock(&qemu_cpu_list_lock);
  81     if (cpu->cpu_index == UNASSIGNED_CPU_INDEX) {
  82         cpu->cpu_index = cpu_get_free_index();
  83         assert(cpu->cpu_index != UNASSIGNED_CPU_INDEX);
  84     } else {
  85         assert(!cpu_index_auto_assigned);
  86     }
  87     QTAILQ_INSERT_TAIL_RCU(&cpus, cpu, node);
  88     qemu_mutex_unlock(&qemu_cpu_list_lock);
  89
  90     finish_safe_work(cpu);
  91 }
  92
  93 void cpu_list_remove(CPUState *cpu)
  94 {
  95     qemu_mutex_lock(&qemu_cpu_list_lock);
  96     if (!QTAILQ_IN_USE(cpu, node)) {
  97         /* there is nothing to undo since cpu_exec_init() hasn't been called */
  98         qemu_mutex_unlock(&qemu_cpu_list_lock);
  99         return;
 100     }
 101
 102     assert(!(cpu_index_auto_assigned && cpu != QTAILQ_LAST(&cpus, CPUTailQ)));
 103
 104     QTAILQ_REMOVE_RCU(&cpus, cpu, node);
 105     cpu->cpu_index = UNASSIGNED_CPU_INDEX;
 106     qemu_mutex_unlock(&qemu_cpu_list_lock);
 107 }
 108
 109 struct qemu_work_item {
 110     struct qemu_work_item *next;
 111     run_on_cpu_func func;
 112     run_on_cpu_data data;
 113     bool free, exclusive, done;
 114 };
 115
 116 static void queue_work_on_cpu(CPUState *cpu, struct qemu_work_item *wi)
 117 {
 118     qemu_mutex_lock(&cpu->work_mutex);
 119     if (cpu->queued_work_first == NULL) {
 120         cpu->queued_work_first = wi;
 121     } else {
 122         cpu->queued_work_last->next = wi;
 123     }
 124     cpu->queued_work_last = wi;
 125     wi->next = NULL;
 126     wi->done = false;
 127     qemu_mutex_unlock(&cpu->work_mutex);
 128
 129     qemu_cpu_kick(cpu);
 130 }
 131
 132 void do_run_on_cpu(CPUState *cpu, run_on_cpu_func func, run_on_cpu_data data,
 133                    QemuMutex *mutex)
 134 {
 135     struct qemu_work_item wi;
 136
 137     if (qemu_cpu_is_self(cpu)) {
 138         func(cpu, data);
 139         return;
 140     }
 141
 142     wi.func = func;
 143     wi.data = data;
 144     wi.done = false;
 145     wi.free = false;
 146     wi.exclusive = false;
 147
 148     queue_work_on_cpu(cpu, &wi);
 149     while (!atomic_mb_read(&wi.done)) {
 150         CPUState *self_cpu = current_cpu;
 151
 152         qemu_cond_wait(&qemu_work_cond, mutex);
 153         current_cpu = self_cpu;
 154     }
 155 }
 156
 157 void async_run_on_cpu(CPUState *cpu, run_on_cpu_func func, run_on_cpu_data data)
 158 {
 159     struct qemu_work_item *wi;
 160
 161     wi = g_malloc0(sizeof(struct qemu_work_item));
 162     wi->func = func;
 163     wi->data = data;
 164     wi->free = true;
 165
 166     queue_work_on_cpu(cpu, wi);
 167 }
 168
 169 /* Wait for pending exclusive operations to complete.  The CPU list lock
 170    must be held.  */
 171 static inline void exclusive_idle(void)
 172 {
 173     while (pending_cpus) {
 174         qemu_cond_wait(&exclusive_resume, &qemu_cpu_list_lock);
 175     }
 176 }
 177
 178 /* Start an exclusive operation.
 179    Must only be called from outside cpu_exec.  */
 180 void start_exclusive(void)
 181 {
 182     CPUState *other_cpu;
 183     int running_cpus;
 184
 185     qemu_mutex_lock(&qemu_cpu_list_lock);
 186     exclusive_idle();
 187
 188     /* Make all other cpus stop executing.  */
 189     atomic_set(&pending_cpus, 1);
 190
 191     /* Write pending_cpus before reading other_cpu->running.  */
 192     smp_mb();
 193     running_cpus = 0;
 194     CPU_FOREACH(other_cpu) {
 195         if (atomic_read(&other_cpu->running)) {
 196             other_cpu->has_waiter = true;
 197             running_cpus++;
 198             qemu_cpu_kick(other_cpu);
 199         }
 200     }
 201
 202     atomic_set(&pending_cpus, running_cpus + 1);
 203     while (pending_cpus > 1) {
 204         qemu_cond_wait(&exclusive_cond, &qemu_cpu_list_lock);
 205     }
 206
 207     /* Can release mutex, no one will enter another exclusive
 208      * section until end_exclusive resets pending_cpus to 0.
 209      */
 210     qemu_mutex_unlock(&qemu_cpu_list_lock);
 211 }
 212
 213 /* Finish an exclusive operation.  */
 214 void end_exclusive(void)
 215 {
 216     qemu_mutex_lock(&qemu_cpu_list_lock);
 217     atomic_set(&pending_cpus, 0);
 218     qemu_cond_broadcast(&exclusive_resume);
 219     qemu_mutex_unlock(&qemu_cpu_list_lock);
 220 }
 221
 222 /* Wait for exclusive ops to finish, and begin cpu execution.  */
 223 void cpu_exec_start(CPUState *cpu)
 224 {
 225     atomic_set(&cpu->running, true);
 226
 227     /* Write cpu->running before reading pending_cpus.  */
 228     smp_mb();
 229
 230     /* 1. start_exclusive saw cpu->running == true and pending_cpus >= 1.
 231      * After taking the lock we'll see cpu->has_waiter == true and run---not
 232      * for long because start_exclusive kicked us.  cpu_exec_end will
 233      * decrement pending_cpus and signal the waiter.
 234      *
 235      * 2. start_exclusive saw cpu->running == false but pending_cpus >= 1.
 236      * This includes the case when an exclusive item is running now.
 237      * Then we'll see cpu->has_waiter == false and wait for the item to
 238      * complete.
 239      *
 240      * 3. pending_cpus == 0.  Then start_exclusive is definitely going to
 241      * see cpu->running == true, and it will kick the CPU.
 242      */
 243     if (unlikely(atomic_read(&pending_cpus))) {
 244         qemu_mutex_lock(&qemu_cpu_list_lock);
 245         if (!cpu->has_waiter) {
 246             /* Not counted in pending_cpus, let the exclusive item
 247              * run.  Since we have the lock, just set cpu->running to true
 248              * while holding it; no need to check pending_cpus again.
 249              */
 250             atomic_set(&cpu->running, false);
 251             exclusive_idle();
 252             /* Now pending_cpus is zero.  */
 253             atomic_set(&cpu->running, true);
 254         } else {
 255             /* Counted in pending_cpus, go ahead and release the
 256              * waiter at cpu_exec_end.
 257              */
 258         }
 259         qemu_mutex_unlock(&qemu_cpu_list_lock);
 260     }
 261 }
 262
 263 /* Mark cpu as not executing, and release pending exclusive ops.  */
 264 void cpu_exec_end(CPUState *cpu)
 265 {
 266     atomic_set(&cpu->running, false);
 267
 268     /* Write cpu->running before reading pending_cpus.  */
 269     smp_mb();
 270
 271     /* 1. start_exclusive saw cpu->running == true.  Then it will increment
 272      * pending_cpus and wait for exclusive_cond.  After taking the lock
 273      * we'll see cpu->has_waiter == true.
 274      *
 275      * 2. start_exclusive saw cpu->running == false but here pending_cpus >= 1.
 276      * This includes the case when an exclusive item started after setting
 277      * cpu->running to false and before we read pending_cpus.  Then we'll see
 278      * cpu->has_waiter == false and not touch pending_cpus.  The next call to
 279      * cpu_exec_start will run exclusive_idle if still necessary, thus waiting
 280      * for the item to complete.
 281      *
 282      * 3. pending_cpus == 0.  Then start_exclusive is definitely going to
 283      * see cpu->running == false, and it can ignore this CPU until the
 284      * next cpu_exec_start.
 285      */
 286     if (unlikely(atomic_read(&pending_cpus))) {
 287         qemu_mutex_lock(&qemu_cpu_list_lock);
 288         if (cpu->has_waiter) {
 289             cpu->has_waiter = false;
 290             atomic_set(&pending_cpus, pending_cpus - 1);
 291             if (pending_cpus == 1) {
 292                 qemu_cond_signal(&exclusive_cond);
 293             }
 294         }
 295         qemu_mutex_unlock(&qemu_cpu_list_lock);
 296     }
 297 }
 298
 299 void async_safe_run_on_cpu(CPUState *cpu, run_on_cpu_func func,
 300                            run_on_cpu_data data)
 301 {
 302     struct qemu_work_item *wi;
 303
 304     wi = g_malloc0(sizeof(struct qemu_work_item));
 305     wi->func = func;
 306     wi->data = data;
 307     wi->free = true;
 308     wi->exclusive = true;
 309
 310     queue_work_on_cpu(cpu, wi);
 311 }
 312
 313 void process_queued_cpu_work(CPUState *cpu)
 314 {
 315     struct qemu_work_item *wi;
 316
 317     if (cpu->queued_work_first == NULL) {
 318         return;
 319     }
 320
 321     qemu_mutex_lock(&cpu->work_mutex);
 322     while (cpu->queued_work_first != NULL) {
 323         wi = cpu->queued_work_first;
 324         cpu->queued_work_first = wi->next;
 325         if (!cpu->queued_work_first) {
 326             cpu->queued_work_last = NULL;
 327         }
 328         qemu_mutex_unlock(&cpu->work_mutex);
 329         if (wi->exclusive) {
 330             /* Running work items outside the BQL avoids the following deadlock:
 331              * 1) start_exclusive() is called with the BQL taken while another
 332              * CPU is running; 2) cpu_exec in the other CPU tries to takes the
 333              * BQL, so it goes to sleep; start_exclusive() is sleeping too, so
 334              * neither CPU can proceed.
 335              */
 336             qemu_mutex_unlock_iothread();
 337             start_exclusive();
 338             wi->func(cpu, wi->data);
 339             end_exclusive();
 340             qemu_mutex_lock_iothread();
 341         } else {
 342             wi->func(cpu, wi->data);
 343         }
 344         qemu_mutex_lock(&cpu->work_mutex);
 345         if (wi->free) {
 346             g_free(wi);
 347         } else {
 348             atomic_mb_set(&wi->done, true);
 349         }
 350     }
 351     qemu_mutex_unlock(&cpu->work_mutex);
 352     qemu_cond_broadcast(&qemu_work_cond);
 353 }