Re: [PATCH] x86: E801 memory "map" use implies no ACPI

[Andrew Cooper <andrew.cooper3@xxxxxxxxxx>]

On 20/11/2020 12:45, Jan Beulich wrote:
> ACPI mandates use of E820 (or newer, e.g. EFI), and in fact firmware
> has been observed to include E820_ACPI ranges in what E801 reports as
> available (really "configured") memory.
>
> Signed-off-by: Jan Beulich <jbeulich@xxxxxxxx>
> ---
> TBD: Alternatively we could drop all use of E801 (and older), since
>      there shouldn't be any 64-bit systems not supporting the more
>      modern E820.

I'd definitely be in favour of deleting the legacy logic.  The very fact
that firmware has been observed to include E820_ACPI in E801 maps shows
that the change here isn't correct in practice.

I think we should go further and depend on the bootloader providing the
memory/video/etc details, which also rips out a lot of 16bit handling
code in the trampoline.

Judging by the context below, I think we should also drop various ACPI
related options.  Given its ubiquity these days, turning various bits of
ACPI off is only going to make problems worse.

~Andrew