cpu: introduce cpu_in_exclusive_context()

Suggested-by: Alex Bennée <alex.bennee@linaro.org>
Reviewed-by: Alex Bennée <alex.bennee@linaro.org>
Signed-off-by: Emilio G. Cota <cota@braap.org>
[AJB: moved inside start/end_exclusive fns + cleanup]
Signed-off-by: Alex Bennée <alex.bennee@linaro.org>
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>

accel/tcg/cpu-exec.c

@@ -238,8 +238,6 @@ void cpu_exec_step_atomic(CPUState *cpu)
     uint32_t flags;
     uint32_t cflags = 1;
     uint32_t cf_mask = cflags & CF_HASH_MASK;
-    /* volatile because we modify it between setjmp and longjmp */
-    volatile bool in_exclusive_region = false;
 
     if (sigsetjmp(cpu->jmp_env, 0) == 0) {
         tb = tb_lookup__cpu_state(cpu, &pc, &cs_base, &flags, cf_mask);
@@ -253,7 +251,6 @@ void cpu_exec_step_atomic(CPUState *cpu)
 
         /* Since we got here, we know that parallel_cpus must be true.  */
         parallel_cpus = false;
-        in_exclusive_region = true;
         cc->cpu_exec_enter(cpu);
         /* execute the generated code */
         trace_exec_tb(tb, pc);
@@ -273,7 +270,7 @@ void cpu_exec_step_atomic(CPUState *cpu)
         assert_no_pages_locked();
     }
 
-    if (in_exclusive_region) {
+    if (cpu_in_exclusive_context(cpu)) {
         /* We might longjump out of either the codegen or the
          * execution, so must make sure we only end the exclusive
          * region if we started it.

cpus-common.c

@@ -200,11 +200,15 @@ void start_exclusive(void)
      * 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);
     atomic_set(&pending_cpus, 0);
     qemu_cond_broadcast(&exclusive_resume);

include/hw/core/cpu.h

@@ -372,6 +372,7 @@ struct CPUState {
     bool unplug;
     bool crash_occurred;
     bool exit_request;
+    bool in_exclusive_context;
     uint32_t cflags_next_tb;
     /* updates protected by BQL */
     uint32_t interrupt_request;
@@ -783,6 +784,18 @@ void async_run_on_cpu(CPUState *cpu, run_on_cpu_func func, run_on_cpu_data data)
  */
 void async_safe_run_on_cpu(CPUState *cpu, run_on_cpu_func func, run_on_cpu_data data);
 
+/**
+ * cpu_in_exclusive_context()
+ * @cpu: The vCPU to check
+ *
+ * Returns true if @cpu is an exclusive context, for example running
+ * something which has previously been queued via async_safe_run_on_cpu().
+ */
+static inline bool cpu_in_exclusive_context(const CPUState *cpu)
+{
+    return cpu->in_exclusive_context;
+}
+
 /**
  * qemu_get_cpu:
  * @index: The CPUState@cpu_index value of the CPU to obtain.