cpus: introduce cpu_update_icount helper

By holding off updates to timer_state.qemu_icount we can run into
trouble when the non-vCPU thread needs to know the time. This helper
ensures we atomically update timers_state.qemu_icount based on what
has been currently executed.
Signed-off-by: NAlex Bennée <alex.bennee@linaro.org>

cpus.c

@@ -232,12 +232,31 @@ static int64_t cpu_get_icount_executed(CPUState *cpu)
     return cpu->icount_budget - (cpu->icount_decr.u16.low + cpu->icount_extra);
 }
 
+/*
+ * Update the global shared timer_state.qemu_icount to take into
+ * account executed instructions. This is done by the TCG vCPU
+ * thread so the main-loop can see time has moved forward.
+ */
+void cpu_update_icount(CPUState *cpu)
+{
+    int64_t executed = cpu_get_icount_executed(cpu);
+    cpu->icount_budget -= executed;
+
+#ifdef CONFIG_ATOMIC64
+    atomic_set__nocheck(&timers_state.qemu_icount,
+                        atomic_read__nocheck(&timers_state.qemu_icount) +
+                        executed);
+#else /* FIXME: we need 64bit atomics to do this safely */
+    timers_state.qemu_icount += executed;
+#endif
+}
+
 int64_t cpu_get_icount_raw(void)
 {
     int64_t icount;
     CPUState *cpu = current_cpu;
 
-    icount = timers_state.qemu_icount;
+    icount = atomic_read(&timers_state.qemu_icount);
     if (cpu && cpu->running) {
         if (!cpu->can_do_io) {
             fprintf(stderr, "Bad icount read\n");
@@ -1220,7 +1239,7 @@ static void process_icount_data(CPUState *cpu)
 {
     if (use_icount) {
         /* Account for executed instructions */
-        timers_state.qemu_icount += cpu_get_icount_executed(cpu);
+        cpu_update_icount(cpu);
 
         /* Reset the counters */
         cpu->icount_decr.u16.low = 0;

include/qemu/timer.h

@@ -869,6 +869,7 @@ int64_t cpu_get_icount_raw(void);
 int64_t cpu_get_icount(void);
 int64_t cpu_get_clock(void);
 int64_t cpu_icount_to_ns(int64_t icount);
+void    cpu_update_icount(CPUState *cpu);
 
 /*******************************************/
 /* host CPU ticks (if available) */