It's FOSS - https://itsfoss.com/lkml-website-down/
Speculation: it must be somehow related to that Meltdown bug.
Reality: the website goes down because it is hosted on a home server that suffered a power outage and needed the password to boot. Problem was that owner Jasper was on vacation when this incident happened.
Just to clarify, lkml.org, one of the many websites that host the Linux Kernel Mailing List archive. It is not the official archive.
lkml.org is managed by Jasper