cpus-common.c

   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 "hw/core/cpu.h"
  24 #include "sysemu/cpus.h"
  25 #include "qemu/lockable.h"
  26
  27 static QemuMutex qemu_cpu_list_lock;
  28 static QemuCond exclusive_cond;
  29 static QemuCond exclusive_resume;
  30 static QemuCond qemu_work_cond;
  31
  32 /* >= 1 if a thread is inside start_exclusive/end_exclusive.  Written
  33  * under qemu_cpu_list_lock, read with atomic operations.
  34  */
  35 static int pending_cpus;
  36
  37 void qemu_init_cpu_list(void)
  38 {
  39     /* This is needed because qemu_init_cpu_list is also called by the
  40      * child process in a fork.  */
  41     pending_cpus = 0;
  42
  43     qemu_mutex_init(&qemu_cpu_list_lock);
  44     qemu_cond_init(&exclusive_cond);
  45     qemu_cond_init(&exclusive_resume);
  46     qemu_cond_init(&qemu_work_cond);
  47 }
  48
  49 void cpu_list_lock(void)
  50 {
  51     qemu_mutex_lock(&qemu_cpu_list_lock);
  52 }
  53
  54 void cpu_list_unlock(void)
  55 {
  56     qemu_mutex_unlock(&qemu_cpu_list_lock);
  57 }
  58
  59 static bool cpu_index_auto_assigned;
  60
  61 static int cpu_get_free_index(void)
  62 {
  63     CPUState *some_cpu;
  64     int max_cpu_index = 0;
  65
  66     cpu_index_auto_assigned = true;
  67     CPU_FOREACH(some_cpu) {
  68         if (some_cpu->cpu_index >= max_cpu_index) {
  69             max_cpu_index = some_cpu->cpu_index + 1;
  70         }
  71     }
  72     return max_cpu_index;
  73 }
  74
  75 CPUTailQ cpus = QTAILQ_HEAD_INITIALIZER(cpus);
  76
  77 void cpu_list_add(CPUState *cpu)
  78 {
  79     QEMU_LOCK_GUARD(&qemu_cpu_list_lock);
  80     if (cpu->cpu_index == UNASSIGNED_CPU_INDEX) {
  81         cpu->cpu_index = cpu_get_free_index();
  82         assert(cpu->cpu_index != UNASSIGNED_CPU_INDEX);
  83     } else {
  84         assert(!cpu_index_auto_assigned);
  85     }
  86     QTAILQ_INSERT_TAIL_RCU(&cpus, cpu, node);
  87 }
  88
  89 void cpu_list_remove(CPUState *cpu)
  90 {
  91     QEMU_LOCK_GUARD(&qemu_cpu_list_lock);
  92     if (!QTAILQ_IN_USE(cpu, node)) {
  93         /* there is nothing to undo since cpu_exec_init() hasn't been called */
  94         return;
  95     }
  96
  97     QTAILQ_REMOVE_RCU(&cpus, cpu, node);
  98     cpu->cpu_index = UNASSIGNED_CPU_INDEX;
  99 }
 100
 101 CPUState *qemu_get_cpu(int index)
 102 {
 103     CPUState *cpu;
 104
 105     CPU_FOREACH(cpu) {
 106         if (cpu->cpu_index == index) {
 107             return cpu;
 108         }
 109     }
 110
 111     return NULL;
 112 }
 113
 114 /* current CPU in the current thread. It is only valid inside cpu_exec() */
 115 __thread CPUState *current_cpu;
 116
 117 struct qemu_work_item {
 118     QSIMPLEQ_ENTRY(qemu_work_item) node;
 119     run_on_cpu_func func;
 120     run_on_cpu_data data;
 121     bool free, exclusive, done;
 122 };
 123
 124 static void queue_work_on_cpu(CPUState *cpu, struct qemu_work_item *wi)
 125 {
 126     qemu_mutex_lock(&cpu->work_mutex);
 127     QSIMPLEQ_INSERT_TAIL(&cpu->work_list, wi, node);
 128     wi->done = false;
 129     qemu_mutex_unlock(&cpu->work_mutex);
 130
 131     qemu_cpu_kick(cpu);
 132 }
 133
 134 void do_run_on_cpu(CPUState *cpu, run_on_cpu_func func, run_on_cpu_data data,
 135                    QemuMutex *mutex)
 136 {
 137     struct qemu_work_item wi;
 138
 139     if (qemu_cpu_is_self(cpu)) {
 140         func(cpu, data);
 141         return;
 142     }
 143
 144     wi.func = func;
 145     wi.data = data;
 146     wi.done = false;
 147     wi.free = false;
 148     wi.exclusive = false;
 149
 150     queue_work_on_cpu(cpu, &wi);
 151     while (!qatomic_mb_read(&wi.done)) {
 152         CPUState *self_cpu = current_cpu;
 153
 154         qemu_cond_wait(&qemu_work_cond, mutex);
 155         current_cpu = self_cpu;
 156     }
 157 }
 158
 159 void async_run_on_cpu(CPUState *cpu, run_on_cpu_func func, run_on_cpu_data data)
 160 {
 161     struct qemu_work_item *wi;
 162
 163     wi = g_malloc0(sizeof(struct qemu_work_item));
 164     wi->func = func;
 165     wi->data = data;
 166     wi->free = true;
 167
 168     queue_work_on_cpu(cpu, wi);
 169 }
 170
 171 /* Wait for pending exclusive operations to complete.  The CPU list lock
 172    must be held.  */
 173 static inline void exclusive_idle(void)
 174 {
 175     while (pending_cpus) {
 176         qemu_cond_wait(&exclusive_resume, &qemu_cpu_list_lock);
 177     }
 178 }
 179
 180 /* Start an exclusive operation.
 181    Must only be called from outside cpu_exec.  */
 182 void start_exclusive(void)
 183 {
 184     CPUState *other_cpu;
 185     int running_cpus;
 186
 187     qemu_mutex_lock(&qemu_cpu_list_lock);
 188     exclusive_idle();
 189
 190     /* Make all other cpus stop executing.  */
 191     qatomic_set(&pending_cpus, 1);
 192
 193     /* Write pending_cpus before reading other_cpu->running.  */
 194     smp_mb();
 195     running_cpus = 0;
 196     CPU_FOREACH(other_cpu) {
 197         if (qatomic_read(&other_cpu->running)) {
 198             other_cpu->has_waiter = true;
 199             running_cpus++;
 200             qemu_cpu_kick(other_cpu);
 201         }
 202     }
 203
 204     qatomic_set(&pending_cpus, running_cpus + 1);
 205     while (pending_cpus > 1) {
 206         qemu_cond_wait(&exclusive_cond, &qemu_cpu_list_lock);
 207     }
 208
 209     /* Can release mutex, no one will enter another exclusive
 210      * section until end_exclusive resets pending_cpus to 0.
 211      */
 212     qemu_mutex_unlock(&qemu_cpu_list_lock);
 213
 214     current_cpu->in_exclusive_context = true;
 215 }
 216
 217 /* Finish an exclusive operation.  */
 218 void end_exclusive(void)
 219 {
 220     current_cpu->in_exclusive_context = false;
 221
 222     qemu_mutex_lock(&qemu_cpu_list_lock);
 223     qatomic_set(&pending_cpus, 0);
 224     qemu_cond_broadcast(&exclusive_resume);
 225     qemu_mutex_unlock(&qemu_cpu_list_lock);
 226 }
 227
 228 /* Wait for exclusive ops to finish, and begin cpu execution.  */
 229 void cpu_exec_start(CPUState *cpu)
 230 {
 231     qatomic_set(&cpu->running, true);
 232
 233     /* Write cpu->running before reading pending_cpus.  */
 234     smp_mb();
 235
 236     /* 1. start_exclusive saw cpu->running == true and pending_cpus >= 1.
 237      * After taking the lock we'll see cpu->has_waiter == true and run---not
 238      * for long because start_exclusive kicked us.  cpu_exec_end will
 239      * decrement pending_cpus and signal the waiter.
 240      *
 241      * 2. start_exclusive saw cpu->running == false but pending_cpus >= 1.
 242      * This includes the case when an exclusive item is running now.
 243      * Then we'll see cpu->has_waiter == false and wait for the item to
 244      * complete.
 245      *
 246      * 3. pending_cpus == 0.  Then start_exclusive is definitely going to
 247      * see cpu->running == true, and it will kick the CPU.
 248      */
 249     if (unlikely(qatomic_read(&pending_cpus))) {
 250         QEMU_LOCK_GUARD(&qemu_cpu_list_lock);
 251         if (!cpu->has_waiter) {
 252             /* Not counted in pending_cpus, let the exclusive item
 253              * run.  Since we have the lock, just set cpu->running to true
 254              * while holding it; no need to check pending_cpus again.
 255              */
 256             qatomic_set(&cpu->running, false);
 257             exclusive_idle();
 258             /* Now pending_cpus is zero.  */
 259             qatomic_set(&cpu->running, true);
 260         } else {
 261             /* Counted in pending_cpus, go ahead and release the
 262              * waiter at cpu_exec_end.
 263              */
 264         }
 265     }
 266 }
 267
 268 /* Mark cpu as not executing, and release pending exclusive ops.  */
 269 void cpu_exec_end(CPUState *cpu)
 270 {
 271     qatomic_set(&cpu->running, false);
 272
 273     /* Write cpu->running before reading pending_cpus.  */
 274     smp_mb();
 275
 276     /* 1. start_exclusive saw cpu->running == true.  Then it will increment
 277      * pending_cpus and wait for exclusive_cond.  After taking the lock
 278      * we'll see cpu->has_waiter == true.
 279      *
 280      * 2. start_exclusive saw cpu->running == false but here pending_cpus >= 1.
 281      * This includes the case when an exclusive item started after setting
 282      * cpu->running to false and before we read pending_cpus.  Then we'll see
 283      * cpu->has_waiter == false and not touch pending_cpus.  The next call to
 284      * cpu_exec_start will run exclusive_idle if still necessary, thus waiting
 285      * for the item to complete.
 286      *
 287      * 3. pending_cpus == 0.  Then start_exclusive is definitely going to
 288      * see cpu->running == false, and it can ignore this CPU until the
 289      * next cpu_exec_start.
 290      */
 291     if (unlikely(qatomic_read(&pending_cpus))) {
 292         QEMU_LOCK_GUARD(&qemu_cpu_list_lock);
 293         if (cpu->has_waiter) {
 294             cpu->has_waiter = false;
 295             qatomic_set(&pending_cpus, pending_cpus - 1);
 296             if (pending_cpus == 1) {
 297                 qemu_cond_signal(&exclusive_cond);
 298             }
 299         }
 300     }
 301 }
 302
 303 void async_safe_run_on_cpu(CPUState *cpu, run_on_cpu_func func,
 304                            run_on_cpu_data data)
 305 {
 306     struct qemu_work_item *wi;
 307
 308     wi = g_malloc0(sizeof(struct qemu_work_item));
 309     wi->func = func;
 310     wi->data = data;
 311     wi->free = true;
 312     wi->exclusive = true;
 313
 314     queue_work_on_cpu(cpu, wi);
 315 }
 316
 317 void process_queued_cpu_work(CPUState *cpu)
 318 {
 319     struct qemu_work_item *wi;
 320
 321     qemu_mutex_lock(&cpu->work_mutex);
 322     if (QSIMPLEQ_EMPTY(&cpu->work_list)) {
 323         qemu_mutex_unlock(&cpu->work_mutex);
 324         return;
 325     }
 326     while (!QSIMPLEQ_EMPTY(&cpu->work_list)) {
 327         wi = QSIMPLEQ_FIRST(&cpu->work_list);
 328         QSIMPLEQ_REMOVE_HEAD(&cpu->work_list, node);
 329         qemu_mutex_unlock(&cpu->work_mutex);
 330         if (wi->exclusive) {
 331             /* Running work items outside the BQL avoids the following deadlock:
 332              * 1) start_exclusive() is called with the BQL taken while another
 333              * CPU is running; 2) cpu_exec in the other CPU tries to takes the
 334              * BQL, so it goes to sleep; start_exclusive() is sleeping too, so
 335              * neither CPU can proceed.
 336              */
 337             qemu_mutex_unlock_iothread();
 338             start_exclusive();
 339             wi->func(cpu, wi->data);
 340             end_exclusive();
 341             qemu_mutex_lock_iothread();
 342         } else {
 343             wi->func(cpu, wi->data);
 344         }
 345         qemu_mutex_lock(&cpu->work_mutex);
 346         if (wi->free) {
 347             g_free(wi);
 348         } else {
 349             qatomic_mb_set(&wi->done, true);
 350         }
 351     }
 352     qemu_mutex_unlock(&cpu->work_mutex);
 353     qemu_cond_broadcast(&qemu_work_cond);
 354 }