Add VM pause support

Check if Qemu wants to pause VM. If yes, don't enter guest. This is
used in snapshot scenario that Qemu pauses VM and tell HAXM not to
enter guest after it finishes the last guest IO/MMIO instruction.

Signed-off-by: Hang Yuan <hang.yuan@intel.com>

core/vcpu.c

@@ -1711,6 +1711,14 @@ int vcpu_execute(struct vcpu_t *vcpu)
             goto out;
         }
     }
+
+    // Check if Qemu pauses VM
+    if (htun->_exit_reason == HAX_EXIT_PAUSED) {
+        htun->_exit_status = HAX_EXIT_PAUSED;
+        hax_log(HAX_LOGD, "vcpu paused\n");
+        goto out;
+    }
+
     err = cpu_vmx_execute(vcpu, htun);
     vcpu_is_panic(vcpu);
 out: