/* * 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); }