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原文摘要

Modern DRAM chips are vulnerable to read disturbance, which manifests as bitflips in a victim row physically near an aggressor row that is repeatedly activated. State-of-the-art mitigations rely on accurate and exhaustive profiling of the read disturbance threshold (RDT), i.e., the minimum number of aggressor row activations needed to induce the first bitflip. However, RDT changes significantly and unpredictably over time, motivating online profilers that dynamically adjust a mitigation's RDT configuration. RDT profiling is costly for online profilers (e.g., hundreds of seconds for a 16-bank DDR4 module) because 1) measuring a single DRAM row's RDT requires many activations and 2) each DRAM row can have a different RDT, requiring many rows to be profiled. We introduce HARE, an online RDT profiling technique that intentionally exacerbates read disturbance to quickly profile a DRAM module. HARE's key idea is to reduce the timing constraints between consecutive DRAM commands during profiling. Doing so significantly reduces profiling time by 1) directly reducing the execution time of the profiling command sequence and 2) exacerbating read disturbance such that the first bitflip occurs at a smaller activation count than with the conventional RowHammer sequence. From our characterization of 180 real DDR4 DRAM chips from four major DRAM manufacturers, we make three observations. First, HARE measures a DRAM row's RDT 31.2% faster than the RowHammer profiler and a DRAM module's minimum RDT with an average reduction of 21.7%. Second, HARE flips more than 95% of the cells that the RowHammer pattern flips. Third, HARE preserves the RDT ranking of rows well enough such that it can exhaustively reprofile a small set of rows to improve its minimum RDT estimation. Our end-to-end evaluations show that HARE enables significant system performance improvements and outperforms the RowHammer profiler.