On 29 September 2015 at 11:12, Ingo Molnar <mingo@xxxxxxxxxx> wrote: > > * Ard Biesheuvel <ard.biesheuvel@xxxxxxxxxx> 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. > OK, fair enough. I agree that setting the flag for 32-bit would be semantically correct. I will leave it to Matt to comment whether it is reasonable in terms of changes to other parts of the code. Thanks, Ard. -- To unsubscribe from this list: send the line "unsubscribe linux-efi" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html