Boosting Inter-process Communication with Architectural Support

IPC (inter-process communication) is a critical mechanism for modern OSes, including not only microkernels such as seL4, QNX, and Fuchsia where system functionalities are deployed in user-level processes, but also monolithic kernels like Android where apps frequently communicate with plenty of user-level services. However, existing IPC mechanisms still suffer from long latency. Previous software optimizations of IPC usually cannot bypass the kernel that is responsible for domain switching and message copying/remapping across different address spaces; hardware solutions such as tagged memory or capability replace page tables for isolation, but usually require non-trivial modification to existing software stack to adapt to the new hardware primitives. In this article, we propose a hardware-assisted OS primitive, XPC (Cross Process Call), for efficient and secure synchronous IPC. XPC enables direct switch between IPC caller and callee without trapping into the kernel and supports secure message passing across multiple processes without copying. We have implemented a prototype of XPC based on the ARM AArch64 with Gem5 simulator and RISC-V architecture with FPGA boards. The evaluation shows that XPC can reduce IPC call latency from 664 to 21 cycles, 14×–123× improvement on Android Binder (ARM), and improve the performance of real-world applications on microkernels by 1.6× on Sqlite3.