SgInt: Safeguarding Interrupts for Hardware-Based I/O Virtualization for Mixed-Criticality Embedded Real-Time Systems Using Non Transparent Bridges

Safety critical systems and in particular higher functional integrated systems like mixed-criticality systems in avionics require a safeguarding that functionalities cannot interfere with each other. A notably underestimated issue are I/O devices and their (message-signaled) interrupts. Message-signaled interrupts are the omnipresent type of interrupts in modern serial high-speed I/O subsystems. These interrupts can be considered as small DMA write packets. If there is no safeguarding for interrupts, an I/O device associated with a distinct functionality can trigger any interrupt or manipulate any control register like triggering reset of all processing cores to provoke a complete system failure. This is a particular issue for available embedded processor architectures, since they do not provide adequate means for interrupt separation like an IOMMU with a granularity sufficient for interrupts. This paper presents the SgInt concept to enable the safeguarding of interrupts for hardware-based I/O virtualization for safety-critical and mixed-criticality embedded real-time systems using non-transparent bridges in single (multi-core) processor systems and multi (multi-core) processor systems. The advantage of this SgInt concept is that it is an general and reusable interrupt separation solution which is scalable from a single (multi-core) processor to a multi (multi-core) processor system and builds on available COTS chip solutions. It allows to upgrade spatial separation for interrupts to available processors having no means for interrupt separation. A practical evaluation shows that the SgInt concept provides the required spatial separation and even slightly outperforms state-of-the-art doorbell interrupt handling in transfer time and transfer rate (by about 0.04%).