Re: [PATCH v7 6/6] x86/efi: Safely enable unaccepted memory in UEFI

Dave Hansen
2023-04-04T19:28:38Z

On 4/4/23 11:09, Kirill A. Shutemov wrote:
>> If our AMD friends don't do this, what is their alternative?
> The alternative is coordination on the host side: VMM can load a BIOS that
> pre-accepts all memory if the kernel is older.
>
> I know that it is not convenient for VMM, but it is technically possible.

Yeah, either a specific BIOS or a knob to tell the BIOS what it has to
do. But, either way, that requires coordination between the BIOS (or
BIOS configuration) and the specific guest. I can see why that's
unpalatable.

> Introduce an ABI with an expiration date is much more ugly. And nobody
> will care about the expiration date, until you will try to remove it.

Yeah, the only real expiration date for an ABI is "never". I don't
believe for a second that we'll ever be able to remove the interface.

Either way, I'd love to hear more from folks about why a BIOS-side
option (configuration or otherwise) is not a good option. I know we've
discussed this in a few mail threads, but it would be even better to get
it into the cover letter or documentation.