https://wccftech.com/intel-mds-vulnerabilities-affecting-7th-gen-and-below-may-slow-macs-by-up-to-40-apple-warns/

Intel recently disclosed vulnerabilities related to its Microarchitectural Data Sampling technique (another speculative execution attack vector) and Apple has rolled out an advisory that full mitigation of MDS may reduce performance by up to 40% in some cases. While hardware level mitigation is present in 8th Generation Intel processors and above – this does spell trouble for security conscious users running 7th gen hardware and below.

Intel Hyper Threading is the feature most closely associated with the MDS attack vector and while turning it off wont keep you safe from all speculative execution attack vectors, it will protect you from this particular variant. Here is what Apple had to say about the situation: