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 }