The Linux kernel developers hate their solution, and they only used it because they can't think of a better one. It causes enormous increases in complexity and kills performance in many cases.
They revived previous work on this as part of the KAISER work in November 2017, and still had major bugs with it in February 2018 (ie, 4 months later). That's pretty similar to the 6 month timeline mentioned here.
The essential element of the solution for Meltdown is the same in every x86-64 OS: unmapping the kernel when in usermode. This is widely hated because it makes kernel entries and exits much slower, and blows away the TLB if your hardware doesn't have PCID support.
They revived previous work on this as part of the KAISER work in November 2017, and still had major bugs with it in February 2018 (ie, 4 months later). That's pretty similar to the 6 month timeline mentioned here.
https://lwn.net/Articles/738975/
https://arstechnica.com/gadgets/2018/01/whats-behind-the-int...