Re: [PATCH 1/2] x86/efi: Map EFI memmap entries in-order at runtime

From	Ingo Molnar <mingo@kernel.org>
Newsgroups	linux.kernel
Subject	Re: [PATCH 1/2] x86/efi: Map EFI memmap entries in-order at runtime
Date	2015-09-29 11:20 +0200
Message-ID	<qdZeQ-2b3-45@gated-at.bofh.it> (permalink)
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* Ard Biesheuvel <ard.biesheuvel@linaro.org> wrote:

> > except that I don't think
> > the condition on 64-bit makes any sense:
> >
> > +       if (!efi_enabled(EFI_OLD_MEMMAP) && efi_enabled(EFI_64BIT)) {
> >
> > I can see us being nervous wrt. backported patches, but is there any strong reason
> > to not follow this up with a third (non-backported) patch that changes this to:
> >
> > +       if (!efi_enabled(EFI_OLD_MEMMAP)) {
> >
> > for v4.4?
> >
> 
> The 32-bit side essentially implements the old memmap only, which is the the 
> bottom-up version. So old memmap will be implied by 32-bit but not set in the 
> EFI flags, resulting in the reverse enumeration being used with the bottom-up 
> mapping logic. The net result of that is that we create the same problem for 
> 32-bit that we are trying to solve for 64-bit, i.e., the regions will end up in 
> reverse order in the VA mapping.
> 
> To deobfuscate this particular conditional, we could set EFI_OLD_MEMMAP 
> unconditionally on 32-bit x86. Or we could reshuffle variables and conditionals 
> in various other way.

Setting EFI_OLD_MEMMAP would be fine, if doing that has no bad side effects.

> [...] I am not convinced that the overall end result will be any better though.

That's not true, we change an obscure, implicit dependency on 32-bit detail to an 
explicit EFI_OLD_MEMMAP flag that shows exactly what's happening. That's a clear 
improvement.

Thanks,

	Ingo
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Thread

[PATCH 1/2] x86/efi: Map EFI memmap entries in-order at runtime Matt Fleming <matt@codeblueprint.co.uk> - 2015-09-26 00:10 +0200
  Re: [PATCH 1/2] x86/efi: Map EFI memmap entries in-order at runtime Ingo Molnar <mingo@kernel.org> - 2015-09-26 08:00 +0200
    Re: [PATCH 1/2] x86/efi: Map EFI memmap entries in-order at runtime Ard Biesheuvel <ard.biesheuvel@linaro.org> - 2015-09-26 08:50 +0200
    Re: [PATCH 1/2] x86/efi: Map EFI memmap entries in-order at runtime Matt Fleming <matt@codeblueprint.co.uk> - 2015-09-26 15:50 +0200
      Re: [PATCH 1/2] x86/efi: Map EFI memmap entries in-order at runtime Ingo Molnar <mingo@kernel.org> - 2015-09-27 09:10 +0200
        Re: [PATCH 1/2] x86/efi: Map EFI memmap entries in-order at runtime Ard Biesheuvel <ard.biesheuvel@linaro.org> - 2015-09-28 08:50 +0200
          Re: [PATCH 1/2] x86/efi: Map EFI memmap entries in-order at runtime Ingo Molnar <mingo@kernel.org> - 2015-09-28 10:30 +0200
            Re: [PATCH 1/2] x86/efi: Map EFI memmap entries in-order at runtime Ard Biesheuvel <ard.biesheuvel@linaro.org> - 2015-09-28 12:00 +0200
              Re: [PATCH 1/2] x86/efi: Map EFI memmap entries in-order at runtime Ingo Molnar <mingo@kernel.org> - 2015-09-29 11:20 +0200
                Re: [PATCH 1/2] x86/efi: Map EFI memmap entries in-order at runtime Ard Biesheuvel <ard.biesheuvel@linaro.org> - 2015-09-29 12:50 +0200
                Re: [PATCH 1/2] x86/efi: Map EFI memmap entries in-order at runtime Matt Fleming <matt@codeblueprint.co.uk> - 2015-09-29 16:20 +0200
                Re: [PATCH 1/2] x86/efi: Map EFI memmap entries in-order at runtime Matt Fleming <matt@codeblueprint.co.uk> - 2015-09-29 16:00 +0200
    Re: [PATCH 1/2] x86/efi: Map EFI memmap entries in-order at runtime Andy Lutomirski <luto@amacapital.net> - 2015-09-26 19:10 +0200
      Re: [PATCH 1/2] x86/efi: Map EFI memmap entries in-order at runtime "H. Peter Anvin" <hpa@zytor.com> - 2015-09-26 19:30 +0200
        Re: [PATCH 1/2] x86/efi: Map EFI memmap entries in-order at runtime Ard Biesheuvel <ard.biesheuvel@linaro.org> - 2015-09-26 20:20 +0200
          Re: [PATCH 1/2] x86/efi: Map EFI memmap entries in-order at runtime Matt Fleming <matt@codeblueprint.co.uk> - 2015-09-26 22:00 +0200
            Re: [PATCH 1/2] x86/efi: Map EFI memmap entries in-order at runtime Ard Biesheuvel <ard.biesheuvel@linaro.org> - 2015-09-26 22:10 +0200
              Re: [PATCH 1/2] x86/efi: Map EFI memmap entries in-order at runtime "H. Peter Anvin" <hpa@zytor.com> - 2015-09-26 22:30 +0200
                Re: [PATCH 1/2] x86/efi: Map EFI memmap entries in-order at runtime Andy Lutomirski <luto@amacapital.net> - 2015-09-27 18:40 +0200
                Re: [PATCH 1/2] x86/efi: Map EFI memmap entries in-order at runtime Matthew Garrett <mjg59@srcf.ucam.org> - 2015-09-27 20:40 +0200
                Re: [PATCH 1/2] x86/efi: Map EFI memmap entries in-order at runtime Ingo Molnar <mingo@kernel.org> - 2015-09-28 08:20 +0200
                Re: [PATCH 1/2] x86/efi: Map EFI memmap entries in-order at runtime Matthew Garrett <mjg59@srcf.ucam.org> - 2015-09-28 09:10 +0200
                Re: [PATCH 1/2] x86/efi: Map EFI memmap entries in-order at runtime Laszlo Ersek <lersek@redhat.com> - 2015-09-30 00:00 +0200
                Re: [PATCH 1/2] x86/efi: Map EFI memmap entries in-order at runtime Ard Biesheuvel <ard.biesheuvel@linaro.org> - 2015-09-30 11:40 +0200
                Re: [PATCH 1/2] x86/efi: Map EFI memmap entries in-order at runtime Andy Lutomirski <luto@amacapital.net> - 2015-09-30 18:50 +0200
                Re: [PATCH 1/2] x86/efi: Map EFI memmap entries in-order at runtime James Bottomley <jbottomley@odin.com> - 2015-09-30 19:30 +0200
                Re: [PATCH 1/2] x86/efi: Map EFI memmap entries in-order at runtime "H. Peter Anvin" <hpa@zytor.com> - 2015-09-30 03:00 +0200
          Re: [PATCH 1/2] x86/efi: Map EFI memmap entries in-order at runtime "H. Peter Anvin" <hpa@zytor.com> - 2015-09-26 22:00 +0200
        Re: [PATCH 1/2] x86/efi: Map EFI memmap entries in-order at runtime Matt Fleming <matt@codeblueprint.co.uk> - 2015-09-26 22:00 +0200
      Re: [PATCH 1/2] x86/efi: Map EFI memmap entries in-order at runtime Ingo Molnar <mingo@kernel.org> - 2015-09-27 09:00 +0200
  [tip:core/urgent] x86/efi:   Fix boot crash by mapping EFI memmap entries bottom-up at runtime,   instead of top-down tip-bot for Matt Fleming <tipbot@zytor.com> - 2015-10-01 15:00 +0200
    Re: [tip:core/urgent] x86/efi: Fix boot crash by mapping EFI memmap  entries bottom-up at runtime, instead of top-down Matt Fleming <matt@codeblueprint.co.uk> - 2015-10-02 11:50 +0200

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