DIVIDE: Efficient RowHammer Defense via In-DRAM Cache-Based Hot Data Isolation

RowHammer poses a serious reliability challenge to modern DRAM systems. As technology scales down, DRAM resistance to RowHammer has decreased by 30× over the past decade, causing an increasing number of benign applications to suffer from this issue. However, existing defense mechanisms have three limitations: 1) they rely on inefficient mitigation techniques, such as time-consuming victim row refresh; 2) they do not reduce the number of effective RowHammer attacks, leading to frequent mitigations; and 3) they fail to recognize that frequently accessed data is not only a root cause of RowHammer but also presents an opportunity for performance optimization. <p xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">In this paper, we observe that frequently accessed hot data plays a distinct role in security and efficiency: it can induce RowHammer by interfering with adjacent cold data, while also being performance-critical due to its frequent accesses. To this end, we propose Data Isolation via In-DRAM Cache (DIVIDE), a novel defense mechanism that leverages in-DRAM cache to isolate and exploit hot data. DIVIDE offers three key benefits: 1) It reduces the number of effective RowHammer attacks, as hot data in the cache cannot interfere with each other. 2) It provides a simple yet effective mitigation measure by isolating hot data from cold data. 3) It caches frequently accessed hot data, improving average access latency. DIVIDE employs a two-level protection structure: the first level mitigates RowHammer in cache arrays with high efficiency, while the second level addresses the remaining threats in normal arrays to ensure complete protection. Owing to the high in-DRAM cache hit rate, DIVIDE efficiently mitigates RowHammer while preserving both the performance and energy efficiency of the in-DRAM cache. At a RowHammer threshold of 128, DIVIDE with probabilistic mitigation achieves an average performance improvement of 19.6% and energy savings of 20.4% over DDR4 DRAM for fourcore workloads. Compared to an unprotected in-DRAM cache DRAM, DIVIDE incurs only a 2.1% performance overhead while requiring just a modest 1KB per-channel CAM in the memory controller, with no modification to the DRAM chip.