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Re: [tip:efi/core] x86/mm/pat: Use _PAGE_GLOBAL bit for EFI page table mappings

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On Wed, Feb 24, 2016 at 11:45 AM, Matt Fleming <matt@codeblueprint.co.uk> wrote:
> On Wed, 24 Feb, at 10:56:13AM, Linus Torvalds wrote:
>> On Wed, Feb 24, 2016 at 8:36 AM, Andy Lutomirski <luto@amacapital.net> wrote:
>> >>
>> >> So the EFI runtime crap should not change once it is mapped. And those
>> >> should be global. It is only natural.
>> >
>> > Why is it natural?
>> >
>> > Long-term, I'd rather see EFI runtime services use an actual mm_struct
>> > and use_mm.
>>
>> Definitely.
>>
>> The EFI runtime page mapping may be unchanging, but that doesn't mean
>> we should be mapping it all the time - the mapping may not change, but
>> we will change away from it.
>
> There is movement towards hanging the EFI memory map off of mm_struct
> for x86. ARM and arm64 already do this and there were some patches
> from Sylvain (Cc'd) to do this for the purposes of having a task
> context that could be preempted while in the middle of an EFI runtime
> call for some Intel platforms,
>
>   https://lkml.kernel.org/r/1452702762-27216-4-git-send-email-sylvain.chouleur@gmail.com
>
> Apart from the code simplification and not being required to open-code
> the %cr3 diddling, are there other benefits of mm_struct and use_mm()
> that make it appealing in the non-preemptible case?
>
> Not that those aren't reasons enough.

If we add PCID support, then use_mm will get the benefits (~200ns
savings for a round trip) for free.

>
>> So marking those pages global is very wrong.
>
> Ingo, Andy, how do you want to handle this patch? Maybe just drop it
> from tip/efi/core while we prod around making all the EFI mappings
> non-global? Nothing else depends on it, it can be dropped without any
> harm.

If the patch is harmless as is, I'm okay with letting it stay.

--Andy

-- 
Andy Lutomirski
AMA Capital Management, LLC

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[tip:efi/core] x86/mm/pat: Use _PAGE_GLOBAL bit for EFI page table mappings tip-bot for Sai Praneeth <tipbot@zytor.com>@zytor.com - 2016-02-23 10:20 +0100
  Re: [tip:efi/core] x86/mm/pat: Use _PAGE_GLOBAL bit for EFI page  table mappings Andy Lutomirski <luto@amacapital.net> - 2016-02-23 18:50 +0100
    Re: [tip:efi/core] x86/mm/pat: Use _PAGE_GLOBAL bit for EFI page  table mappings Linus Torvalds <torvalds@linux-foundation.org> - 2016-02-23 19:10 +0100
      Re: [tip:efi/core] x86/mm/pat: Use _PAGE_GLOBAL bit for EFI page  table mappings Borislav Petkov <bp@alien8.de> - 2016-02-23 19:20 +0100
      Re: [tip:efi/core] x86/mm/pat: Use _PAGE_GLOBAL bit for EFI page table mappings "H. Peter Anvin" <hpa@zytor.com> - 2016-02-24 03:20 +0100
      Re: [tip:efi/core] x86/mm/pat: Use _PAGE_GLOBAL bit for EFI page table mappings "H. Peter Anvin" <hpa@zytor.com> - 2016-02-24 03:20 +0100
      Re: [tip:efi/core] x86/mm/pat: Use _PAGE_GLOBAL bit for EFI page  table mappings Ingo Molnar <mingo@kernel.org> - 2016-02-25 10:00 +0100
    Re: [tip:efi/core] x86/mm/pat: Use _PAGE_GLOBAL bit for EFI page  table mappings Sai Praneeth Prakhya <sai.praneeth.prakhya@intel.com> - 2016-02-24 02:00 +0100
      Re: [tip:efi/core] x86/mm/pat: Use _PAGE_GLOBAL bit for EFI page  table mappings Andy Lutomirski <luto@amacapital.net> - 2016-02-24 03:50 +0100
        Re: [tip:efi/core] x86/mm/pat: Use _PAGE_GLOBAL bit for EFI page  table mappings Matt Fleming <matt@codeblueprint.co.uk> - 2016-02-24 15:20 +0100
          Re: [tip:efi/core] x86/mm/pat: Use _PAGE_GLOBAL bit for EFI page  table mappings Borislav Petkov <bp@alien8.de> - 2016-02-24 17:30 +0100
            Re: [tip:efi/core] x86/mm/pat: Use _PAGE_GLOBAL bit for EFI page  table mappings Andy Lutomirski <luto@amacapital.net> - 2016-02-24 17:40 +0100
              Re: [tip:efi/core] x86/mm/pat: Use _PAGE_GLOBAL bit for EFI page  table mappings Linus Torvalds <torvalds@linux-foundation.org> - 2016-02-24 20:00 +0100
                Re: [tip:efi/core] x86/mm/pat: Use _PAGE_GLOBAL bit for EFI page  table mappings Matt Fleming <matt@codeblueprint.co.uk> - 2016-02-24 20:50 +0100
                Re: [tip:efi/core] x86/mm/pat: Use _PAGE_GLOBAL bit for EFI page  table mappings Andy Lutomirski <luto@amacapital.net> - 2016-02-24 21:00 +0100
                Re: [tip:efi/core] x86/mm/pat: Use _PAGE_GLOBAL bit for EFI page  table mappings Sylvain Chouleur <sylvain.chouleur@gmail.com> - 2016-02-29 12:00 +0100
                Re: [tip:efi/core] x86/mm/pat: Use _PAGE_GLOBAL bit for EFI page  table mappings Matt Fleming <matt@codeblueprint.co.uk> - 2016-03-02 12:30 +0100
              Re: [tip:efi/core] x86/mm/pat: Use _PAGE_GLOBAL bit for EFI page  table mappings Matt Fleming <matt@codeblueprint.co.uk> - 2016-02-24 20:40 +0100
                Re: [tip:efi/core] x86/mm/pat: Use _PAGE_GLOBAL bit for EFI page  table mappings Andy Lutomirski <luto@amacapital.net> - 2016-02-24 21:00 +0100
                Re: [tip:efi/core] x86/mm/pat: Use _PAGE_GLOBAL bit for EFI page  table mappings Ingo Molnar <mingo@kernel.org> - 2016-02-25 10:10 +0100
                Re: [tip:efi/core] x86/mm/pat: Use _PAGE_GLOBAL bit for EFI page  table mappings Matt Fleming <matt@codeblueprint.co.uk> - 2016-02-25 16:30 +0100
            Re: [tip:efi/core] x86/mm/pat: Use _PAGE_GLOBAL bit for EFI page  table mappings Andy Lutomirski <luto@amacapital.net> - 2016-02-24 17:50 +0100
            Re: [tip:efi/core] x86/mm/pat: Use _PAGE_GLOBAL bit for EFI page  table mappings Borislav Petkov <bp@alien8.de> - 2016-02-24 17:50 +0100
          Re: [tip:efi/core] x86/mm/pat: Use _PAGE_GLOBAL bit for EFI page  table mappings Andy Lutomirski <luto@amacapital.net> - 2016-02-24 17:50 +0100
            Re: [tip:efi/core] x86/mm/pat: Use _PAGE_GLOBAL bit for EFI page  table mappings Matt Fleming <matt@codeblueprint.co.uk> - 2016-02-25 17:10 +0100

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