Messages in this thread | | | Date | Tue, 29 Sep 2015 11:12:30 +0200 | From | Ingo Molnar <> | Subject | Re: [PATCH 1/2] x86/efi: Map EFI memmap entries in-order at runtime |
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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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