Understanding the Overheads of Hardware and Language-Based IPC Mechanisms

ABSTRACTA recent surge of security attacks has triggered a renewed interest in hardware support for isolation. Extended page table switching with VMFUNC, memory protection keys (MPK), and memory tagging extensions (MTE) are just a few of the hardware isolation mechanisms that promise support for low-overhead isolation in recent CPUs. Along with the restored interest in lightweight hardware isolation mechanisms, safe programming languages like Rust has made a leap towards practical, zero-overhead safety implemented without garbage collection. Both lightweight hardware mechanisms and zero-overhead language safety can be leveraged to enforce the isolation of subsystems, e.g., browser plugins, device drivers and kernel extensions, user-defined database and network functions, etc. However, as both technologies are still young, their relative advantages are still unknown. In this work, we study the overheads of hardware and software isolation mechanisms with the goal to understand their relative advantages and disadvantages for fine-grained isolation of subsystems with tight performance budgets. We ask two questions: What is the overhead of hardware isolation in an ideal scenario where the hardware isolation mechanism takes zero cycles? And if the safety of the Rust language can lower the overhead of cross-subsystem invocations, can the language on its own introduce overheads that might outweigh isolation advantages? To answer these questions, we develop and compare two carefully optimized versions of inter-process communication (IPC) mechanisms (one in safe Rust and one in a carefully-optimized assembly), and two identical (to the degree possible) DPDK-based network packet processing frameworks (one in C++ and one in Rust). Our analysis shows that for systems requiring frequent boundary crossings, a safe language is still beneficial even if the overheads of hardware isolation mechanisms drop to zero.