On 8 September 2015 at 15:16, Matt Fleming <m...@codeblueprint.co.uk> wrote: > On Fri, 04 Sep, at 08:53:36PM, Ard Biesheuvel wrote: >> On 4 September 2015 at 20:23, Matt Fleming <m...@codeblueprint.co.uk> wrote: >> > On Fri, 04 Sep, at 03:24:21PM, Ard Biesheuvel wrote: >> >> >> >> Since the UEFI spec does not mandate an enumeration order for >> >> GetMemoryMap(), it seems to me that you still need to sort its output >> >> before laying out the VA space. Since you need to sort it anyway, why >> >> not simply sort it in reverse order and keep all the original code? >> >> Considering that this is meant for stable, that would keep the delta >> >> *much* smaller. >> > >> > Hmm... that'd be a neat trick and while it would save on the diff >> > size, I don't think it would be smaller in terms of change complexity. >> > >> > EDK2 sorts the memory map when EFI_PROPERTIES_TABLE is enabled, so we >> > can be reasonably sure the entry order returned by GetMemoryMap() is >> > compatible with the split regions, even if it's not mandated by the >> > spec. >> > >> >> EDK2 does sort it, but the spec does not mandate it so another >> implementation may do something different entirely. > > Yeah, we should get that requirement added to the spec. > >> > For the non-EFI_PROPERTIES_TABLE case, things have been working fine >> > without the sorting, so I'm reluctant to introduce it now (it's also >> > much less of an issue there). >> > >> >> I see. I do wonder, since the VA mapping preserves the modulo 2 MB >> alignment of each region, aren't you using much more VA space when >> mapping in reverse order as you are doing now? > > It doesn't enforce a 2MB alignment for every entry, just those that > are actually 2MB aligned. This should be exactly what was done in the > previous version of the code. Do you see a bug? >
I noticed that the 64-bit version of efi_map_region() preserves the relative alignment with respect to a 2 MB boundary for /each/ region. Since the regions are mapped in reverse order, it is highly unlikely that each region starts at the same 2 MB relative alignment that the previous region ended at, so you are likely wasting quite a bit of VA space. I don't think it is a bug, though, but it does not seem intentional. -- Ard. -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
