Farina, Giorgio (2024) Assessing and improving isolation in real-time cloud platforms. [Tesi di dottorato]

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Abstract

Real-time cloud foresees the porting of critical applications to cloud platforms, in order to enable cloud benefits for critical scenarios, such as ease of usability and reconfiguration, as well as higher scalability and availability. However, this vision has been limited by several threats that live within cloud platforms, mostly related to the sharing of resources. In order to support real-time cloud vision, this thesis focuses on two key limitations of the emerging real-time cloud paradigm: memory access isolation and failure isolation across execution environments hosted on the same hardware platform. Regarding memory isolation, this thesis addressed the challenge of evaluating a black-box hardware controller, called "Memory Bandwidth Allocation", available on new Intel server processors, by developing a workload capable of bypassing the regulation shown by generic state-of-the-art workloads by over 50%, warning the community about the risks of adopting generic workloads for specialized controllers. To improve bandwidth utilization, this thesis also provided empirical evidence that memory queue occupancy can detect the interference degree, i.e., the number of memory contenders, within one-fifth of the regulation period. In terms of failure isolation, this thesis introduced a novel record and replay method to assess hypervisor robustness without manual effort, focusing on the shared, privileged software layer running across customers. This thesis implemented a proof-of-concept tool called IRIS within the Xen hypervisor. The results demonstrated that IRIS could generate new test cases, reaching valid hypervisor states with significant time improvements (from 42.5% to 99.6%) and high accuracy, with code coverage fitting between 92.1% and 100% compared to the recorded execution.

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