Intel has disclosed vulnerabilities called Microarchitectural Data Sampling (MDS) that apply to desktop and notebook computers with Intel CPUs, including all modern Mac computers.

Although there are no known exploits affecting customers at the time of this writing, customers who believe their computer is at heightened risk of attack can use the Terminal app to enable an additional CPU instruction and disable hyper-threading processing technology, which provides full protection from these security issues.

This option is available for macOS Mojave, High Sierra and Sierra and may have a significant impact on the performance of your computer.

Testing conducted by Apple in May 2019 showed as much as a 40 percent reduction in performance with tests that include multithreaded workloads and public benchmarks. Performance tests are conducted using specific Mac computers. Actual results will vary based on model, configuration, usage, and other factors.

And

Microarchitectural Data Sampling (MDS) is already addressed at the hardware level in many of our recent 8th and 9th Generation Intel® Core™ processors, as well as the 2nd Generation Intel® Xeon® Scalable Processor Family. For other affected products, mitigation is available through microcode updates, coupled with corresponding updates to operating system and hypervisor software that are available starting today.

It is quite obvious that Intel story that they only recently became aware about it is bullshit, as we clearly see that this time all impact is on older processors and suddenly new ones do not have this "new" issue.

It is also becoming clear why Microsoft are so eager to install Windows 10 with its automatically installed updates on all older PCs, as this will allow pair to gradually slow down your computer.

Make sure to expect more of similar things during this year. If Intel will keep killing speculative predictions more they could drop performance further 20-30%. Next can be some hole in vector instructions to disable them for older CPUs.