cpus: make pause_all_cpus() play with SMP on single threaded TCG

pause_all_cpus() is sometimes called from a VCPU thread (e.g. s390x
during special reset). It cannot deal with multiple VCPUs per Thread
(single threaded TCG) yet.

Booting an s390x guest with -smp 2 and single threaded TCG from disk
currently fails. The DIAG 308 will issue a pause_all_cpus() and wait
forever for the CPUs to actually stop. But it is waiting for itself.

So let's stop all VCPUs belonging to the current thread. Factor out
stopping of a VCPU.

Signed-off-by: David Hildenbrand <david@redhat.com>
Message-Id: <20171129191215.11323-1-david@redhat.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

cpus.c

@@ -1057,13 +1057,22 @@ static void qemu_tcg_destroy_vcpu(CPUState *cpu)
 {
 }
 
+static void qemu_cpu_stop(CPUState *cpu, bool exit)
+{
+    g_assert(qemu_cpu_is_self(cpu));
+    cpu->stop = false;
+    cpu->stopped = true;
+    if (exit) {
+        cpu_exit(cpu);
+    }
+    qemu_cond_broadcast(&qemu_pause_cond);
+}
+
 static void qemu_wait_io_event_common(CPUState *cpu)
 {
     atomic_mb_set(&cpu->thread_kicked, false);
     if (cpu->stop) {
-        cpu->stop = false;
-        cpu->stopped = true;
-        qemu_cond_broadcast(&qemu_pause_cond);
+        qemu_cpu_stop(cpu, false);
     }
     process_queued_cpu_work(cpu);
 }
@@ -1610,12 +1619,12 @@ void pause_all_vcpus(void)
 
     qemu_clock_enable(QEMU_CLOCK_VIRTUAL, false);
     CPU_FOREACH(cpu) {
-        cpu->stop = true;
-        qemu_cpu_kick(cpu);
-    }
-
-    if (qemu_in_vcpu_thread()) {
-        cpu_stop_current();
+        if (qemu_cpu_is_self(cpu)) {
+            qemu_cpu_stop(cpu, true);
+        } else {
+            cpu->stop = true;
+            qemu_cpu_kick(cpu);
+        }
     }
 
     while (!all_vcpus_paused()) {
@@ -1799,10 +1808,7 @@ void qemu_init_vcpu(CPUState *cpu)
 void cpu_stop_current(void)
 {
     if (current_cpu) {
-        current_cpu->stop = false;
-        current_cpu->stopped = true;
-        cpu_exit(current_cpu);
-        qemu_cond_broadcast(&qemu_pause_cond);
+        qemu_cpu_stop(current_cpu, true);
     }
 }