Intel is today making public the Jump Conditional Code (JCC) erratum. This is a bug involving the CPU's Decoded ICache where on Skylake and derived CPUs where unpredictable behavior could happen when jump instructions cross cache lines. Unfortunately addressing this error in software comes with a performance penalty but ultimately Intel engineers are working to offset that through a toolchain update.

Intel's official guidance coming out today states their observed performance effects from this microcode update to be in the range of 0~4% but with some "outliers higher than the 0~4% range."