Modern Intel, AMD, and ARM processors translate complex instructions into simpler internal micro-ops that are then cached in a dedicated on-chip structure called the micro-op cache. This work presents an in-depth characterization study of the micro-op cache, reverse-engineering many undocumented features, and further describes attacks that exploit the micro-op cache as a timing channel to transmit secret information. In particular, this paper describes three attacks – (1) a same thread cross-domain attack that leaks secrets across the user-kernel boundary, (2) a cross-SMT thread attack that transmits secrets across two SMT threads via the micro-op cache, and (3) transient execution attacks that have the ability to leak an unauthorized secret accessed along a misspeculated path, even before the transient instruction is dispatched to execution, breaking several existing invisible speculation and fencing-based solutions that mitigate Spectre.

Memory hierarchy performance, specifically cache memory capacity, is a constraining factor in the performance of modern computers. This paper presents the results of two-level cache memory simulations and examines the impact of exclusive caching on system performance. Exclusive caching enables higher capacity with the same cache area by eliminating redundant copies. The experiments presented compare an exclusive cache hierarchy with an inclusive cache hierarchy utilizing similar L1 and L2 parameters. Experiments indicate that significant performance advantages can be gained for some benchmark through the use of an exclusive organization. The performance differences are illustrated using the L2 cache misses and execution time metrics. The most significant improvement shown is a 16% reduction in execution time, with an average reduction of 8% for the smallest cache configuration tested. With equal size victim buffer and victim cache for exclusive and inclusive cache hierarchies respectively, some benchmarks show increased execution time for exclusive caches because a victim cache can reduce conflict misses significantly while a victim buffer can introduce worst-case penalties. Considering the inconsistent performance improvement, the increased complexity of an exclusive cache hierarchy needs to be justified based upon the specifics of the application and system.