Re: [PATCHv1, RFC 0/8] Boot-time switching between 4- and 5-level paging

[Linus Torvalds]

On Thu, May 25, 2017 at 1:33 PM, Kirill A. Shutemov
<kirill.shutemov@xxxxxxxxxxxxxxx> wrote:
> Here' my first attempt to bring boot-time between 4- and 5-level paging.
> It looks not too terrible to me. I've expected it to be worse.

If I read this right, you just made it a global on/off thing.

May I suggest possibly a different model entirely? Can you make it a
per-mm flag instead?

And then we

 (a) make all kthreads use the 4-level page tables

 (b) which means that all the init code uses the 4-level page tables

 (c) which means that all those checks for "start_secondary" etc can
just go away, because those all run with 4-level page tables.

Or is it just much too expensive to switch between 4-level and 5-level
paging at run-time?

              Linus