cpus-common.c - qemu - Git at Google

 /*
  * 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;

     if (current_cpu->exclusive_context_count) {
         current_cpu->exclusive_context_count++;
         return;
     }

     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->exclusive_context_count = 1;
 }

 /* Finish an exclusive operation.  */
 void end_exclusive(void)
 {
     current_cpu->exclusive_context_count--;
     if (current_cpu->exclusive_context_count) {
         return;
     }

     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);
 }
	/*
	* 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;

	if (current_cpu->exclusive_context_count) {
	current_cpu->exclusive_context_count++;
	return;
	}

	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->exclusive_context_count = 1;
	}

	/* Finish an exclusive operation. */
	void end_exclusive(void)
	{
	current_cpu->exclusive_context_count--;
	if (current_cpu->exclusive_context_count) {
	return;
	}

	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);
	}