accel: use atomic accesses for exit_request

CPU threads write exit_request as a "note to self" that they need to
go out to a slow path.  This write happens out of the BQL and can be
a data race with another threads' cpu_exit(); use atomic accesses
consistently.

While at it, change the source argument from int ("1") to bool ("true").

Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Reviewed-by: Philippe Mathieu-Daudé <philmd@linaro.org>
Reviewed-by: Peter Xu <peterx@redhat.com>
Reviewed-by: Igor Mammedov <imammedo@redhat.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

accel/kvm/kvm-all.c

@@ -3730,7 +3730,7 @@ int kvm_on_sigbus_vcpu(CPUState *cpu, int code, void *addr)
     have_sigbus_pending = true;
     pending_sigbus_addr = addr;
     pending_sigbus_code = code;
-    qatomic_set(&cpu->exit_request, 1);
+    qatomic_set(&cpu->exit_request, true);
     return 0;
 #else
     return 1;

accel/tcg/tcg-accel-ops-mttcg.c

@@ -85,7 +85,7 @@ static void *mttcg_cpu_thread_fn(void *arg)
     qemu_guest_random_seed_thread_part2(cpu->random_seed);
 
     /* process any pending work */
-    cpu->exit_request = 1;
+    qatomic_set(&cpu->exit_request, true);
 
     do {
         if (cpu_can_run(cpu)) {

accel/tcg/tcg-accel-ops-rr.c

@@ -212,7 +212,7 @@ static void *rr_cpu_thread_fn(void *arg)
     cpu = first_cpu;
 
     /* process any pending work */
-    cpu->exit_request = 1;
+    qatomic_set(&cpu->exit_request, true);
 
     while (1) {
         /* Only used for icount_enabled() */
@@ -293,7 +293,7 @@ static void *rr_cpu_thread_fn(void *arg)
         /* Does not need a memory barrier because a spurious wakeup is okay.  */
         qatomic_set(&rr_current_cpu, NULL);
 
-        if (cpu && cpu->exit_request) {
+        if (cpu && qatomic_read(&cpu->exit_request)) {
             qatomic_set_mb(&cpu->exit_request, 0);
         }
 

hw/ppc/spapr_hcall.c

@@ -509,7 +509,7 @@ static target_ulong h_cede(PowerPCCPU *cpu, SpaprMachineState *spapr,
     if (!cpu_has_work(cs)) {
         cs->halted = 1;
         cs->exception_index = EXCP_HLT;
-        cs->exit_request = 1;
+        qatomic_set(&cs->exit_request, true);
         ppc_maybe_interrupt(env);
     }
 
@@ -531,7 +531,7 @@ static target_ulong h_confer_self(PowerPCCPU *cpu)
     }
     cs->halted = 1;
     cs->exception_index = EXCP_HALTED;
-    cs->exit_request = 1;
+    qatomic_set(&cs->exit_request, true);
     ppc_maybe_interrupt(&cpu->env);
 
     return H_SUCCESS;
@@ -624,7 +624,7 @@ static target_ulong h_confer(PowerPCCPU *cpu, SpaprMachineState *spapr,
     }
 
     cs->exception_index = EXCP_YIELD;
-    cs->exit_request = 1;
+    qatomic_set(&cs->exit_request, true);
     cpu_loop_exit(cs);
 
     return H_SUCCESS;

include/hw/core/cpu.h

@@ -422,6 +422,15 @@ struct qemu_work_item;
  * valid under cpu_list_lock.
  * @created: Indicates whether the CPU thread has been successfully created.
  * @halt_cond: condition variable sleeping threads can wait on.
+ * @exit_request: Another thread requests the CPU to call qemu_wait_io_event().
+ *   Should be read only by CPU thread with load-acquire, to synchronize with
+ *   other threads' store-release operation.
+ *
+ *   In some cases, accelerator-specific code will write exit_request from
+ *   within the same thread, to "bump" the effect of qemu_cpu_kick() to
+ *   the one provided by cpu_exit(), especially when processing interrupt
+ *   flags.  In this case, the write and read happen in the same thread
+ *   and the write therefore can use qemu_atomic_set().
  * @interrupt_request: Indicates a pending interrupt request.
  *   Only used by system emulation.
  * @halted: Nonzero if the CPU is in suspended state.

target/i386/kvm/kvm.c

@@ -5486,10 +5486,10 @@ void kvm_arch_pre_run(CPUState *cpu, struct kvm_run *run)
     if (cpu_test_interrupt(cpu, CPU_INTERRUPT_INIT | CPU_INTERRUPT_TPR)) {
         if (cpu_test_interrupt(cpu, CPU_INTERRUPT_INIT) &&
             !(env->hflags & HF_SMM_MASK)) {
-            qatomic_set(&cpu->exit_request, 1);
+            qatomic_set(&cpu->exit_request, true);
         }
         if (cpu_test_interrupt(cpu, CPU_INTERRUPT_TPR)) {
-            qatomic_set(&cpu->exit_request, 1);
+            qatomic_set(&cpu->exit_request, true);
         }
     }
 
@@ -5604,7 +5604,7 @@ int kvm_arch_process_async_events(CPUState *cs)
         if (env->exception_nr == EXCP08_DBLE) {
             /* this means triple fault */
             qemu_system_reset_request(SHUTDOWN_CAUSE_GUEST_RESET);
-            cs->exit_request = 1;
+            qatomic_set(&cs->exit_request, true);
             return 0;
         }
         kvm_queue_exception(env, EXCP12_MCHK, 0, 0);

target/i386/nvmm/nvmm-accel-ops.c

@@ -77,7 +77,7 @@ static void nvmm_start_vcpu_thread(CPUState *cpu)
  */
 static void nvmm_kick_vcpu_thread(CPUState *cpu)
 {
-    cpu->exit_request = 1;
+    qatomic_set(&cpu->exit_request, true);
     cpus_kick_thread(cpu);
 }
 

target/i386/nvmm/nvmm-all.c

@@ -414,7 +414,7 @@ nvmm_vcpu_pre_run(CPUState *cpu)
      * or commit pending TPR access.
      */
     if (cpu_test_interrupt(cpu, CPU_INTERRUPT_INIT | CPU_INTERRUPT_TPR)) {
-        cpu->exit_request = 1;
+        qatomic_set(&cpu->exit_request, true);
     }
 
     if (!has_event && cpu_test_interrupt(cpu, CPU_INTERRUPT_NMI)) {

target/i386/whpx/whpx-all.c

@@ -1489,10 +1489,10 @@ static void whpx_vcpu_pre_run(CPUState *cpu)
     if (cpu_test_interrupt(cpu, CPU_INTERRUPT_INIT | CPU_INTERRUPT_TPR)) {
         if (cpu_test_interrupt(cpu, CPU_INTERRUPT_INIT) &&
             !(env->hflags & HF_SMM_MASK)) {
-            cpu->exit_request = 1;
+            qatomic_set(&cpu->exit_request, true);
         }
         if (cpu_test_interrupt(cpu, CPU_INTERRUPT_TPR)) {
-            cpu->exit_request = 1;
+            qatomic_set(&cpu->exit_request, true);
         }
     }
 
@@ -1539,7 +1539,7 @@ static void whpx_vcpu_pre_run(CPUState *cpu)
     if (tpr != vcpu->tpr) {
         vcpu->tpr = tpr;
         reg_values[reg_count].Reg64 = tpr;
-        cpu->exit_request = 1;
+        qatomic_set(&cpu->exit_request, true);
         reg_names[reg_count] = WHvX64RegisterCr8;
         reg_count += 1;
     }