On Thu, 30 Jul, at 09:39:47PM, joeyli wrote:
>
> OK, understood! Thanks for your suggestion!
>
> But, I have a question about mapping Boot Code/Data to -4G area. I understand
> we need Runtime regions, and 1:1 mapping is the workaround of some buggy BIOS.
> But why should kernel mapping Boot regions to -4G area?
We map the Boot Service regions in the -4G area for simplicity, i.e.
it's easier to iterate through the EFI memory map in order, and map
things starting at -4G and working down to lower addresses, than it
would be to make different mapping decisions based on the region type.
As for why we map the Boot Service regions *at all*, that's also a bug
workaround, see commit 916f676f8dc0 ("x86, efi: Retain boot service code
until after switching to virtual mode"). We setup the mappings before we
call efi_free_boot_services().
--
Matt Fleming, Intel Open Source Technology Center
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