qemu

cpus-common.c (10508B)

---

 /*
  * CPU thread main loop - common bits for user and system mode emulation
  *
  *  Copyright (c) 2003-2005 Fabrice Bellard
  *
  * This library is free software; you can redistribute it and/or
  * modify it under the terms of the GNU Lesser General Public
  * License as published by the Free Software Foundation; either
  * version 2.1 of the License, or (at your option) any later version.
  *
  * This library is distributed in the hope that it will be useful,
  * but WITHOUT ANY WARRANTY; without even the implied warranty of
  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
  * Lesser General Public License for more details.
  *
  * You should have received a copy of the GNU Lesser General Public
  * License along with this library; if not, see <http://www.gnu.org/licenses/>.
  */
 
 #include "qemu/osdep.h"
 #include "qemu/main-loop.h"
 #include "exec/cpu-common.h"
 #include "hw/core/cpu.h"
 #include "sysemu/cpus.h"
 #include "qemu/lockable.h"
 
 static QemuMutex qemu_cpu_list_lock;
 static QemuCond exclusive_cond;
 static QemuCond exclusive_resume;
 static QemuCond qemu_work_cond;
 
 /* >= 1 if a thread is inside start_exclusive/end_exclusive.  Written
  * under qemu_cpu_list_lock, read with atomic operations.
  */
 static int pending_cpus;
 
 void qemu_init_cpu_list(void)
 {
     /* This is needed because qemu_init_cpu_list is also called by the
      * child process in a fork.  */
     pending_cpus = 0;
 
     qemu_mutex_init(&qemu_cpu_list_lock);
     qemu_cond_init(&exclusive_cond);
     qemu_cond_init(&exclusive_resume);
     qemu_cond_init(&qemu_work_cond);
 }
 
 void cpu_list_lock(void)
 {
     qemu_mutex_lock(&qemu_cpu_list_lock);
 }
 
 void cpu_list_unlock(void)
 {
     qemu_mutex_unlock(&qemu_cpu_list_lock);
 }
 
 static bool cpu_index_auto_assigned;
 
 static int cpu_get_free_index(void)
 {
     CPUState *some_cpu;
     int max_cpu_index = 0;
 
     cpu_index_auto_assigned = true;
     CPU_FOREACH(some_cpu) {
         if (some_cpu->cpu_index >= max_cpu_index) {
             max_cpu_index = some_cpu->cpu_index + 1;
         }
     }
     return max_cpu_index;
 }
 
 CPUTailQ cpus = QTAILQ_HEAD_INITIALIZER(cpus);
 static unsigned int cpu_list_generation_id;
 
 unsigned int cpu_list_generation_id_get(void)
 {
     return cpu_list_generation_id;
 }
 
 void cpu_list_add(CPUState *cpu)
 {
     QEMU_LOCK_GUARD(&qemu_cpu_list_lock);
     if (cpu->cpu_index == UNASSIGNED_CPU_INDEX) {
         cpu->cpu_index = cpu_get_free_index();
         assert(cpu->cpu_index != UNASSIGNED_CPU_INDEX);
     } else {
         assert(!cpu_index_auto_assigned);
     }
     QTAILQ_INSERT_TAIL_RCU(&cpus, cpu, node);
     cpu_list_generation_id++;
 }
 
 void cpu_list_remove(CPUState *cpu)
 {
     QEMU_LOCK_GUARD(&qemu_cpu_list_lock);
     if (!QTAILQ_IN_USE(cpu, node)) {
         /* there is nothing to undo since cpu_exec_init() hasn't been called */
         return;
     }
 
     QTAILQ_REMOVE_RCU(&cpus, cpu, node);
     cpu->cpu_index = UNASSIGNED_CPU_INDEX;
     cpu_list_generation_id++;
 }
 
 CPUState *qemu_get_cpu(int index)
 {
     CPUState *cpu;
 
     CPU_FOREACH(cpu) {
         if (cpu->cpu_index == index) {
             return cpu;
         }
     }
 
     return NULL;
 }
 
 /* current CPU in the current thread. It is only valid inside cpu_exec() */
 __thread CPUState *current_cpu;
 
 struct qemu_work_item {
     QSIMPLEQ_ENTRY(qemu_work_item) node;
     run_on_cpu_func func;
     run_on_cpu_data data;
     bool free, exclusive, done;
 };
 
 static void queue_work_on_cpu(CPUState *cpu, struct qemu_work_item *wi)
 {
     qemu_mutex_lock(&cpu->work_mutex);
     QSIMPLEQ_INSERT_TAIL(&cpu->work_list, wi, node);
     wi->done = false;
     qemu_mutex_unlock(&cpu->work_mutex);
 
     qemu_cpu_kick(cpu);
 }
 
 void do_run_on_cpu(CPUState *cpu, run_on_cpu_func func, run_on_cpu_data data,
                    QemuMutex *mutex)
 {
     struct qemu_work_item wi;
 
     if (qemu_cpu_is_self(cpu)) {
         func(cpu, data);
         return;
     }
 
     wi.func = func;
     wi.data = data;
     wi.done = false;
     wi.free = false;
     wi.exclusive = false;
 
     queue_work_on_cpu(cpu, &wi);
     while (!qatomic_mb_read(&wi.done)) {
         CPUState *self_cpu = current_cpu;
 
         qemu_cond_wait(&qemu_work_cond, mutex);
         current_cpu = self_cpu;
     }
 }
 
 void async_run_on_cpu(CPUState *cpu, run_on_cpu_func func, run_on_cpu_data data)
 {
     struct qemu_work_item *wi;
 
     wi = g_new0(struct qemu_work_item, 1);
     wi->func = func;
     wi->data = data;
     wi->free = true;
 
     queue_work_on_cpu(cpu, wi);
 }
 
 /* Wait for pending exclusive operations to complete.  The CPU list lock
    must be held.  */
 static inline void exclusive_idle(void)
 {
     while (pending_cpus) {
         qemu_cond_wait(&exclusive_resume, &qemu_cpu_list_lock);
     }
 }
 
 /* Start an exclusive operation.
    Must only be called from outside cpu_exec.  */
 void start_exclusive(void)
 {
     CPUState *other_cpu;
     int running_cpus;
 
     qemu_mutex_lock(&qemu_cpu_list_lock);
     exclusive_idle();
 
     /* Make all other cpus stop executing.  */
     qatomic_set(&pending_cpus, 1);
 
     /* Write pending_cpus before reading other_cpu->running.  */
     smp_mb();
     running_cpus = 0;
     CPU_FOREACH(other_cpu) {
         if (qatomic_read(&other_cpu->running)) {
             other_cpu->has_waiter = true;
             running_cpus++;
             qemu_cpu_kick(other_cpu);
         }
     }
 
     qatomic_set(&pending_cpus, running_cpus + 1);
     while (pending_cpus > 1) {
         qemu_cond_wait(&exclusive_cond, &qemu_cpu_list_lock);
     }
 
     /* Can release mutex, no one will enter another exclusive
      * section until end_exclusive resets pending_cpus to 0.
      */
     qemu_mutex_unlock(&qemu_cpu_list_lock);
 
     current_cpu->in_exclusive_context = true;
 }
 
 /* Finish an exclusive operation.  */
 void end_exclusive(void)
 {
     current_cpu->in_exclusive_context = false;
 
     qemu_mutex_lock(&qemu_cpu_list_lock);
     qatomic_set(&pending_cpus, 0);
     qemu_cond_broadcast(&exclusive_resume);
     qemu_mutex_unlock(&qemu_cpu_list_lock);
 }
 
 /* Wait for exclusive ops to finish, and begin cpu execution.  */
 void cpu_exec_start(CPUState *cpu)
 {
     qatomic_set(&cpu->running, true);
 
     /* Write cpu->running before reading pending_cpus.  */
     smp_mb();
 
     /* 1. start_exclusive saw cpu->running == true and pending_cpus >= 1.
      * After taking the lock we'll see cpu->has_waiter == true and run---not
      * for long because start_exclusive kicked us.  cpu_exec_end will
      * decrement pending_cpus and signal the waiter.
      *
      * 2. start_exclusive saw cpu->running == false but pending_cpus >= 1.
      * This includes the case when an exclusive item is running now.
      * Then we'll see cpu->has_waiter == false and wait for the item to
      * complete.
      *
      * 3. pending_cpus == 0.  Then start_exclusive is definitely going to
      * see cpu->running == true, and it will kick the CPU.
      */
     if (unlikely(qatomic_read(&pending_cpus))) {
         QEMU_LOCK_GUARD(&qemu_cpu_list_lock);
         if (!cpu->has_waiter) {
             /* Not counted in pending_cpus, let the exclusive item
              * run.  Since we have the lock, just set cpu->running to true
              * while holding it; no need to check pending_cpus again.
              */
             qatomic_set(&cpu->running, false);
             exclusive_idle();
             /* Now pending_cpus is zero.  */
             qatomic_set(&cpu->running, true);
         } else {
             /* Counted in pending_cpus, go ahead and release the
              * waiter at cpu_exec_end.
              */
         }
     }
 }
 
 /* Mark cpu as not executing, and release pending exclusive ops.  */
 void cpu_exec_end(CPUState *cpu)
 {
     qatomic_set(&cpu->running, false);
 
     /* Write cpu->running before reading pending_cpus.  */
     smp_mb();
 
     /* 1. start_exclusive saw cpu->running == true.  Then it will increment
      * pending_cpus and wait for exclusive_cond.  After taking the lock
      * we'll see cpu->has_waiter == true.
      *
      * 2. start_exclusive saw cpu->running == false but here pending_cpus >= 1.
      * This includes the case when an exclusive item started after setting
      * cpu->running to false and before we read pending_cpus.  Then we'll see
      * cpu->has_waiter == false and not touch pending_cpus.  The next call to
      * cpu_exec_start will run exclusive_idle if still necessary, thus waiting
      * for the item to complete.
      *
      * 3. pending_cpus == 0.  Then start_exclusive is definitely going to
      * see cpu->running == false, and it can ignore this CPU until the
      * next cpu_exec_start.
      */
     if (unlikely(qatomic_read(&pending_cpus))) {
         QEMU_LOCK_GUARD(&qemu_cpu_list_lock);
         if (cpu->has_waiter) {
             cpu->has_waiter = false;
             qatomic_set(&pending_cpus, pending_cpus - 1);
             if (pending_cpus == 1) {
                 qemu_cond_signal(&exclusive_cond);
             }
         }
     }
 }
 
 void async_safe_run_on_cpu(CPUState *cpu, run_on_cpu_func func,
                            run_on_cpu_data data)
 {
     struct qemu_work_item *wi;
 
     wi = g_new0(struct qemu_work_item, 1);
     wi->func = func;
     wi->data = data;
     wi->free = true;
     wi->exclusive = true;
 
     queue_work_on_cpu(cpu, wi);
 }
 
 void process_queued_cpu_work(CPUState *cpu)
 {
     struct qemu_work_item *wi;
 
     qemu_mutex_lock(&cpu->work_mutex);
     if (QSIMPLEQ_EMPTY(&cpu->work_list)) {
         qemu_mutex_unlock(&cpu->work_mutex);
         return;
     }
     while (!QSIMPLEQ_EMPTY(&cpu->work_list)) {
         wi = QSIMPLEQ_FIRST(&cpu->work_list);
         QSIMPLEQ_REMOVE_HEAD(&cpu->work_list, node);
         qemu_mutex_unlock(&cpu->work_mutex);
         if (wi->exclusive) {
             /* Running work items outside the BQL avoids the following deadlock:
              * 1) start_exclusive() is called with the BQL taken while another
              * CPU is running; 2) cpu_exec in the other CPU tries to takes the
              * BQL, so it goes to sleep; start_exclusive() is sleeping too, so
              * neither CPU can proceed.
              */
             qemu_mutex_unlock_iothread();
             start_exclusive();
             wi->func(cpu, wi->data);
             end_exclusive();
             qemu_mutex_lock_iothread();
         } else {
             wi->func(cpu, wi->data);
         }
         qemu_mutex_lock(&cpu->work_mutex);
         if (wi->free) {
             g_free(wi);
         } else {
             qatomic_mb_set(&wi->done, true);
         }
     }
     qemu_mutex_unlock(&cpu->work_mutex);
     qemu_cond_broadcast(&qemu_work_cond);
 }