Meltdown strikes back: the L1 terminal fault vulnerability

We should give kudos to Microsoft here. They thought about the potential risks from tight resource sharing some time ago and obviously were able to invest significantly ahead of any one vulnerability such as this one in secret scrubbing/address space isolation/core scheduling/etc. This is something that we'll need to look at in Linux and other OSes over time if we want to make HT totally safe as well. It's a great example of what's possible, but a big lift. We do need to also get over the mindset that SMT threads are "cores". Especially in projects like OpenStack. An SMT thread is not a core, and we should never treat it as such, but it's easy to think in those terms when looking at /proc/cpuinfo output and just counting "cpus".