Re: [edk2-devel] Side effects of enabling PML5 in EFI

["Gerd Hoffmann" <kraxel@redhat.com>]

On Tue, May 09, 2023 at 06:24:03PM +0100, Pedro Falcato wrote:
> Hi all,
> 
> (+CC people vaguely related to the EFI spec, the PML5 implementation
> and kernel EFI boot code)
> 
> As a result of the latest 5-level paging patches, I've been looking
> into how tiano supports PML5.
> This raised a question: Doesn't enabling PML5 in-firmware break
> compatibility with non-PML5-aware bootloaders and kernels?

kernels yes, bootloaders probably not (unless the bootloader not the
kernel calls exitbootservices).

> So, how is any of this supposed to work?

edk2 is relatively late to the party, so with everybody else supporting
5-level paging already it might not be much of an issue in practice even
though there is no compatibility handling (I know of) in edk2.

When running your operating system museum in virtual machines you have
the option to just turn off 5-level paging support in the virtual cpu.

take care,
  Gerd