/*
* 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 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);
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);
}
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;
}
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_malloc0(sizeof(struct qemu_work_item));
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_malloc0(sizeof(struct qemu_work_item));
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);
}
