Intel DOWNFALL: New Vulnerability Affecting AVX2/AVX-512 With Big Performance Implications

This Patch Tuesday brings a new and potentially painful processor speculative execution vulnerability... Downfall, or as Intel prefers to call it is GDS: Gather Data Sampling. GDS/Downfall affects the gather instruction with AVX2 and AVX-512 enabled processors. At least the latest-generation Intel CPUs are not affected but Tigerlake / Ice Lake back to Skylake is confirmed to be impacted. There is microcode mitigation available but it will be costly for AVX2/AVX-512 workloads with GATHER instructions in hot code-paths and thus widespread software exposure particularly for HPC and other compute-intensive workloads that have relied on AVX2/AVX-512 for better performance.