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Re: [PATCH 2/2] arm64/efi: Don't pad between EFI_MEMORY_RUNTIME regions

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* H. Peter Anvin <hpa@zytor.com> wrote:

> On 09/27/2015 12:06 AM, Ingo Molnar wrote:
> > 
> > * Ard Biesheuvel <ard.biesheuvel@linaro.org> wrote:
> > 
> >>> If we allocate the EFI runtime as a single virtual memory block then issues 
> >>> like rounding between sections does not even come up as a problem: we map the 
> >>> original offsets and sizes byte by byte.
> >>
> >> Well, by that reasoning, we should not call SetVirtualAddressMap() in the first 
> >> place, and just use the 1:1 mapping UEFI uses natively. This is more than 
> >> feasible on arm64, and I actually fought hard against using 
> >> SetVirtualAddressMap() at all, but I was overruled by others. I think this is 
> >> also trivially possible on X64, since the 1:1 mapping is already active 
> >> alongside the VA mapping.
> > 
> > Could we please re-list all the arguments pro and contra of 1:1 physical mappings, 
> > in a post that also explains the background so that more people can chime in, not 
> > just people versed in EFI internals? It's very much possible that a bad decision 
> > was made.
> > 
> 
> Pro: by far the sanest way to map the UEFI tables.
> Con: doesn't actually work (breaks on several known platforms.)

You knew this next question was coming: in what way does it break on known 
platforms?

I.e. do those platforms require a SetVirtualAddressMap() call and break if one 
does not come?

Note that there's 3 models possible:

 - pure 1:1
 - 1:1 plus offset, with SetVirtualAddressMap(offset)
 - bottom up allocator

I don't think we want 'pure' 1:1 physical/virtual (for security reasons, etc.).

So the question is, in what way does our current proposed bottom-up allocator 
differ from 1:1 plus offset? My impression is that they are mostly identical.

Thanks,

	Ingo
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[PATCH 2/2] arm64/efi: Don't pad between EFI_MEMORY_RUNTIME regions Matt Fleming <matt@codeblueprint.co.uk> - 2015-09-26 00:10 +0200
  Re: [PATCH 2/2] arm64/efi: Don't pad between EFI_MEMORY_RUNTIME  regions Ingo Molnar <mingo@kernel.org> - 2015-09-26 08:10 +0200
    Re: [PATCH 2/2] arm64/efi: Don't pad between EFI_MEMORY_RUNTIME regions Ard Biesheuvel <ard.biesheuvel@linaro.org> - 2015-09-26 09:10 +0200
      Re: [PATCH 2/2] arm64/efi: Don't pad between EFI_MEMORY_RUNTIME  regions Ingo Molnar <mingo@kernel.org> - 2015-09-27 09:10 +0200
        Re: [PATCH 2/2] arm64/efi: Don't pad between EFI_MEMORY_RUNTIME  regions Borislav Petkov <bp@alien8.de> - 2015-09-27 12:20 +0200
          Re: [PATCH 2/2] arm64/efi: Don't pad between EFI_MEMORY_RUNTIME  regions Ingo Molnar <mingo@kernel.org> - 2015-09-28 08:30 +0200
          Re: [PATCH 2/2] arm64/efi: Don't pad between EFI_MEMORY_RUNTIME  regions Dave Young <dyoung@redhat.com> - 2015-09-29 11:40 +0200
            Re: [PATCH 2/2] arm64/efi: Don't pad between EFI_MEMORY_RUNTIME  regions Borislav Petkov <bp@alien8.de> - 2015-09-29 12:30 +0200
          Re: [PATCH 2/2] arm64/efi: Don't pad between EFI_MEMORY_RUNTIME  regions Matt Fleming <matt@codeblueprint.co.uk> - 2015-09-29 16:40 +0200
            Re: [PATCH 2/2] arm64/efi: Don't pad between EFI_MEMORY_RUNTIME  regions "H. Peter Anvin" <hpa@zytor.com> - 2015-09-30 03:00 +0200
              Re: [PATCH 2/2] arm64/efi: Don't pad between EFI_MEMORY_RUNTIME  regions Borislav Petkov <bp@alien8.de> - 2015-09-30 10:40 +0200
        Re: [PATCH 2/2] arm64/efi: Don't pad between EFI_MEMORY_RUNTIME  regions "H. Peter Anvin" <hpa@zytor.com> - 2015-09-30 03:10 +0200
          Re: [PATCH 2/2] arm64/efi: Don't pad between EFI_MEMORY_RUNTIME regions Andy Lutomirski <luto@amacapital.net> - 2015-09-30 03:20 +0200
            Re: [PATCH 2/2] arm64/efi: Don't pad between EFI_MEMORY_RUNTIME  regions "H. Peter Anvin" <hpa@zytor.com> - 2015-09-30 03:20 +0200
            Re: [PATCH 2/2] arm64/efi: Don't pad between EFI_MEMORY_RUNTIME regions Ard Biesheuvel <ard.biesheuvel@linaro.org> - 2015-09-30 06:30 +0200
          Re: [PATCH 2/2] arm64/efi: Don't pad between EFI_MEMORY_RUNTIME  regions Ingo Molnar <mingo@kernel.org> - 2015-10-01 12:50 +0200
  [tip:core/urgent] arm64/efi:   Fix boot crash by not padding between EFI_MEMORY_RUNTIME regions tip-bot for Ard Biesheuvel <tipbot@zytor.com> - 2015-10-01 15:00 +0200

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