Scholars studying the CPU vulnerabilities have discovered some risks in the core of the processor. Unlike the high level instructions in Assembler, the core uses a microprogram using some very simple instructions. The microprogramming caches have been found to be at risk,
Recall Spectre and Meltdown a few years ago, The researchers are concerned that abusive code could gain secure access. Reading the paper suggested that redesign of the core will be needed to make it more robust.
Skylake was the main focus but AMD processors are similar. The suggested course of action will be likely to slow performance again until a better solution can be figured out. Intel will need to redesign away from Skylake which is clearly still very problematic. Even the latest Intel processors are drawing a lot from the skylake designs.
Since 2019 when the first crops of faults were patched, it seems that researchers are continuing to examine the CPU manuals from Intel and AMD closely to investigate the processor behaviour.
The modern CPU is not deterministic as to the number of cycles for a result. AMD and Intel processors specify a range of expected clocks for instructions. This makes tuning of code very difficult compared to the earlier 8-bit processors which offed exact clock timings.