Spectre v3, aka Meltdown — CVE-2017-5754
KPTI is the approach adopted by every major operating system, but not everyone implemented it at the same time.
Linux, being included in the embargo, had a mitigation since at least December 2017.
The 4th and 5th of January, DragonflyBSD added a KTPI-like, via 1 2 3 4.
The 7th of January 2018, NetBSD did the same, and the so did FreeBSD on the 19th
In February 2018, Philip Guenther and Mike Larkin implemented an equivalent of KTPI in OpenBSD for AMD64. Although, to be fair, support for ARM64 was added the 10th of January.