https://arstechnica.com/gadgets/2018/01/meltdown-and-spectre-every-modern-
processor-has-unfixable-security-fladdws/U
TL;DR
Windows, Linux, and macOS have all received security patches that
significantly alter how the operating systems handle virtual memory in
order to protect against a hitherto undisclosed flaw.
...
In the immediate term, it looks like most systems will shortly have
patches for Meltdown. At least for Linux and Windows, these patches
allow end-users to opt out if they would prefer. The most vulnerable
users are probably cloud service providers; Meltdown and Spectre can
both in principle be used to further attacks against hypervisors,
making it easier for malicious users to break out of their virtual
machines.
...
For typical desktop users, the risk is arguably less significant. While
both Meltdown and Spectre can have value in expanding the scope of an
existing flaw, neither one is sufficient on its own to, for example,
break out of a Web browser.
Apparent moral of story for CPU: don't speculate (but it's significantly
*slower*).