(There's a link to Sphinx at the bottom of the page)
It looks like this is just generated from Documentation/index.rst and linked pages in the kernel source tree, which seems to have been created less than a year ago: https://github.com/torvalds/linux/commits/master/Documentati...
There's also a copy on kernel. org, not sure why Intel's copy is being linked here. It's probably the same text, so any copy should be equally good, it just feels less canonical to me. Probably silliness on my part for even thinking of it.
> Built with Sphinx using a theme provided by Read the Docs.
John Corbert has done quite a bit recently within Documentation to make it more structured and has (from my understanding) massively revamped the documentation compilation.