TZDKS: A New TrustZone-Based Dual-Criticality System with Balanced Performance

Many mixed-criticality systems are composed of a RTOS (Real-Time Operating System) and a GPOS (General Purpose Operating System), and we define them as mixed-time-sensitive systems. Complexity, isolation, real-time latency, and overhead are the main metrics to evaluate such a mixed-time-sensitive system (MTSS). These metrics may conflict with each other, so it is difficult for them to be consistently optimized. Most existing implementations only optimize part of the above metrics but not all. As the first contribution, this paper provides a detailed analysis of performance influencing factors which are exerted by various runtime mechanisms of existing MTSSs. We figure out the difference in performance across system designs, including task switch, memory management, interrupt handling, and resource isolation. We propose the philosophy of utilizing TrustZone characteristics to optimize various mechanisms in MTSS. The second contribution is to propose a TrustZone-based solution - termed TZDKS - for MTSS. Appropriate utilization of TrustZone extensions helps TZDKS to implement (i) virtualization environment for GPOS and RTOS, (ii) high efficient task switch, memory access, interrupt handling and device access which are verified by experiments. Therefore, TZDKS can achieve a full-scale balance amongst aforementioned metrics.