* Ard Biesheuvel <ardb+git@xxxxxxxxxx> wrote:
> From: Ard Biesheuvel <ardb@xxxxxxxxxx>
>
> Since commit
>
> a1b87d54f4e4 ("x86/efistub: Avoid legacy decompressor when doing EFI boot")
>
> booting via the EFI stub no longer relies on the legacy decompressor,
> and instead, the kernel proper is decompressed by code executing in the
> context of the EFI boot services, and subsequently invoked directly.
>
> The only remaining dependency is the EFI mixed mode startup code, which
> makes a detour via the legacy decompressor's 32-bit entrypoint, in order
> to obtain a 1:1 mapping of memory, which is a prerequisite for 64-bit
> execution on x86.
>
> This detour requires some fiddly setup on the part of the mixed mode
> startup code, which has to stash the firmware stack pointer and boot
> arguments in memory, and create a fake struct boot_params to trick the
> code in startup_32 to behave as intended.
>
> This dependency also impedes reuse of the EFI stub code in other
> contexts, such as generic EFI zboot, which will reuse the EFI stub but
> not the legacy decompressor.
>
> So remove this dependency, by replacing this detour with a minimal
> reimplementation of the 1:1 mapping code. With some further cleanup
> applied on top, the line count barely changes, but the resulting code
> can operate independently from the legacy decompressor, and is therefore
> moved out of arch/x86/boot/compressed and into the EFI libstub/
> directory.
>
> Ard Biesheuvel (6):
> x86/efi/mixed: Check CPU compatibility without relying on verify_cpu()
> x86/efi/mixed: Remove dependency on legacy startup_32 code
> x86/efi/mixed: Don't bother preserving 64-bit mode segment selectors
> x86/efi/mixed: Simplify and document thunking logic
> x86/efi/mixed: Reduce padding by moving some code around
> x86/efi/mixed: Move mixed mode startup code into libstub
>
> arch/x86/boot/compressed/Makefile | 1 -
> arch/x86/boot/compressed/head_64.S | 7 -
> drivers/firmware/efi/libstub/Makefile | 3 +
> arch/x86/boot/compressed/efi_mixed.S => drivers/firmware/efi/libstub/x86-mixed.S | 320 ++++++++++----------
> 4 files changed, 169 insertions(+), 162 deletions(-)
> rename arch/x86/boot/compressed/efi_mixed.S => drivers/firmware/efi/libstub/x86-mixed.S (54%)
A belated:
Acked-by: Ingo Molnar <mingo@xxxxxxxxxx>
Thanks,
Ingo
