qemu/cpus-common.c
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   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
  26static QemuMutex qemu_cpu_list_lock;
  27static QemuCond exclusive_cond;
  28static QemuCond exclusive_resume;
  29static 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 */
  34static int pending_cpus;
  35
  36void 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
  48void cpu_list_lock(void)
  49{
  50    qemu_mutex_lock(&qemu_cpu_list_lock);
  51}
  52
  53void cpu_list_unlock(void)
  54{
  55    qemu_mutex_unlock(&qemu_cpu_list_lock);
  56}
  57
  58static bool cpu_index_auto_assigned;
  59
  60static 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
  72static void finish_safe_work(CPUState *cpu)
  73{
  74    cpu_exec_start(cpu);
  75    cpu_exec_end(cpu);
  76}
  77
  78void 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
  93void 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
 109struct 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
 116static 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
 132void 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
 157void 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.  */
 171static 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.  */
 180void 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.  */
 214void 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.  */
 223void 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.  */
 264void 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
 299void 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
 313void 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}
 354