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

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On Thu, May 25, 2017 at 1:33 PM, Kirill A. Shutemov
<kirill.shutemov@linux.intel.com> 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

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Thread

[PATCHv1, RFC 0/8] Boot-time switching between 4- and 5-level paging "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com> - 2017-05-25 22:40 +0200
  [PATCHv1, RFC 2/8] x86/mm: Make virtual memory layout movable for CONFIG_X86_5LEVEL "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com> - 2017-05-25 22:40 +0200
  Re: [PATCHv1, RFC 0/8] Boot-time switching between 4- and 5-level paging Linus Torvalds <torvalds@linux-foundation.org> - 2017-05-26 01:30 +0200
    Re: [PATCHv1, RFC 0/8] Boot-time switching between 4- and 5-level paging Andy Lutomirski <luto@kernel.org> - 2017-05-26 02:50 +0200
      Re: [PATCHv1, RFC 0/8] Boot-time switching between 4- and 5-level  paging Kevin Easton <kevin@guarana.org> - 2017-05-26 06:30 +0200
        Re: [PATCHv1, RFC 0/8] Boot-time switching between 4- and 5-level paging Andy Lutomirski <luto@kernel.org> - 2017-05-26 09:30 +0200
    Re: [PATCHv1, RFC 0/8] Boot-time switching between 4- and 5-level  paging "Kirill A. Shutemov" <kirill@shutemov.name> - 2017-05-26 15:10 +0200
      Re: [PATCHv1, RFC 0/8] Boot-time switching between 4- and 5-level  paging Andi Kleen <ak@linux.intel.com> - 2017-05-26 15:40 +0200
      Re: [PATCHv1, RFC 0/8] Boot-time switching between 4- and 5-level paging Linus Torvalds <torvalds@linux-foundation.org> - 2017-05-26 18:00 +0200
        Re: [PATCHv1, RFC 0/8] Boot-time switching between 4- and 5-level  paging "Kirill A. Shutemov" <kirill@shutemov.name> - 2017-05-26 18:00 +0200
          Re: [PATCHv1, RFC 0/8] Boot-time switching between 4- and 5-level paging Linus Torvalds <torvalds@linux-foundation.org> - 2017-05-26 18:20 +0200
        Re: [PATCHv1, RFC 0/8] Boot-time switching between 4- and 5-level  paging Dave Hansen <dave.hansen@intel.com> - 2017-05-26 21:30 +0200
          Re: [PATCHv1, RFC 0/8] Boot-time switching between 4- and 5-level paging hpa@zytor.com - 2017-05-26 21:50 +0200
        Re: [PATCHv1, RFC 0/8] Boot-time switching between 4- and 5-level paging hpa@zytor.com - 2017-05-26 21:30 +0200
      Re: [PATCHv1, RFC 0/8] Boot-time switching between 4- and 5-level paging hpa@zytor.com - 2017-05-26 22:20 +0200

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