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

Abstract

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-timesensitive systems. Complexity, isolation, real-time latency, and overhead are the main metrics to evaluate such a mixed-timesensitive 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.

Work-in-Progress: Real-Time RPC for Hybrid Dual-OS System

“…TZDKS [2] is the product of the idea that combines strong points of dual-kernel [2] and virtualization by utilizing Trust-Zone technology [12]. Firstly, TZDKS adopts a dual-kernel structure to support applications of different time-sensitivities.…”

“…There are two different types of RPC, which is classified by the direction of communication. We only discuss the RPC from the RTOS task to an entity in GPOS, and name it RG-RPC, because in most of the cases the RG-RPC requires higher demand for time predictability [2].…”

“…The other method is building the sub-systems in the isolated environment provided as the extension by the SoC hardware, such as ARM TrustZone. For example, TZDKS [2] and LTZVisor [8] proposed multi-OS architectures upon TrustZone, which achieve better system performance.…”

“…In a hybrid multi-OS system, communication is the foundation of inter-operation, and RPC has become a fundamental mechanism [10]. Security and efficiency are the two most important metrics for communication [2]. We note that the time predictability for communication is necessary, because the scheduler should be able to predict the duration time of the communication on the RTOS part.…”

“…• A Real-Time RTOS-GPOS RPC protocol (i.e., RTRG-RPC) on TZDKS [2], with three main mechanisms: SGI (Software Generate Interrupt) messages transforming, interrupt handler RPC serving, and priority-swapping.…”