cpus: document that qemu_cpu_kick() can be used for BQL-less operation

Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

include/hw/core/cpu.h

@@ -829,7 +829,8 @@ bool qemu_cpu_is_self(CPUState *cpu);
  * qemu_cpu_kick:
  * @cpu: The vCPU to kick.
  *
- * Kicks @cpu's thread.
+ * Kicks @cpu's thread to exit the accelerator.  For accelerators that
+ * can do that, the target vCPU thread will try not to take the BQL.
  */
 void qemu_cpu_kick(CPUState *cpu);