Non-uniform hammering produces up to 23,500x more bit flips on ECC-protected NVIDIA GPUs.

GPUThor reverse-engineers GPU memory-access coalescing to build patterns that activate aggressor rows harder than decoy rows, and identifies refresh instances to construct longer patterns escaping in-DRAM mitigations across refresh intervals. Prior GPU Rowhammer work triggered tens to hundreds of flips; this yields 500x to 23,500x more across A4000, A4500, A5000 and A6000 cards, approaching CPU Rowhammer rates. That closes the practicality gap, which matters directly if you rent shared GPU capacity.