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In this paper, we present the design and implementation of an Open Computing Language (OpenCL) framework that targets heterogeneous accelerator multicore architectures with local memory. The architecture consists of a general-purpose processor core and multiple accelerator cores that typically do not have any cache. Each accelerator core, instead, has a small internal local memory. Our OpenCL runtime is based on software-managed caches and coherence protocols that guarantee OpenCL memory consistency to overcome the limited size of the local memory. To boost performance, the runtime relies on three source-code transformation techniques, work-item coalescing, web-based variable expansion and preload-poststore buffering, performed by our OpenCL C source-to-source translator. Work-item coalescing is a procedure to serialize multiple SPMD-like tasks that execute concurrently in the presence of barriers and to sequentially run them on a single accelerator core. It requires the webbased variable expansion technique to allocate local memory for private variables. Preload-poststore buffering is a buffering technique that eliminates the overhead of software cache accesses. Together with work-item coalescing, it has a synergistic effect on boosting performance. We show the effectiveness of our OpenCL framework, evaluating its performance with a system that consists of two Cell BE processors. The experimental result shows that our approach is promising.

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In this paper we present a multi-layer mandatory access control mechanism (ACM) for mobile devices based on system virtualization technology. We discuss a detailed threat model to mobile devices in the real world to develop an ACM fitted to mobile devices. Then, we propose a novel multi-layer access control mechanism for mobile devices, which provides strong protection against the identified mobile threats as well as performance efficiency. Our Virtual Machine Monitor (VMM) and secure domain have independent access control modules to effectively control mobile device's resources. Access control module at VMM controls access requests from a domain to physical/virtual resources in order to confine sharing resources among domains for confidentiality. It also protects a mobile device against DoS attacks draining limited system resources such as battery and memory to guarantee availability. In addition, access control at secure domain enforces fine-grained control of resources (e.g., file system access control) in upper layer without degrading performance of a mobile device due to additional hypercall invocations. Furthermore, there is no bypass of our access control since our ACM is placed inside VMM which is simple and small enough to verify its safety and we eliminated the chance of VMM corruption by checking integrity of VMM including ACM during bootstrap time.

Owing to the benefits of system virtualization, even CE devices have come to take advantage of the technology. However, due to the lack of windowing system which fits virtualization-based CE devices, it is not only inefficient but also difficult for end users to utilize the CE devices running multiple domains. In this paper we present an effective virtual window system for CE devices based on system virtualization. Our approach has three major advantages: (1) by modifying X window system, it provides shared windowing services between domains without dependency of a specific network protocol; (2) by providing a unified graphical user interface which integrates icons of all the applications from every domain, it frees users from remembering which applications are located in which domain and from doing tedious operations for application launching and installation; (3) it provides efficiency in terms of size (storage and memory) and performance to CE devices. We have implemented a prototype of the virtual window system on the basis of Secure Xen on ARM. Our evaluation shows that our approach is usable and efficient enough to be practically adopted for CE devices based on system virtualization.