In this paper, we address latency issue in Xen-ARM virtual machines. Despite the advantages of virtualization in mobile systems, the current Xen-ARM is difficult to apply to mobile devices because it has unpredictable I/O latency. This paper analyzes the latency of incoming packet handling in Xen-ARM, and presents how virtualization affects the latency in detail. To make the latency predictable, firstly, we modify Xen-ARM scheduler so that the driver domain can be promptly scheduled by the hypervisor. Secondly, we introduce additional paravirtualization of guest OS that minimizes non-preemptible code path. With our enhancements, 99% of incoming packets are predictably handled within one millisecond at the destined guest OS, which is a feasible time bound for most soft real-time applications.