Re: [edk2-rfc] [edk2-devel] [RFC] Support Both MM Traditional and Standalone Drivers with One MM Core

["Ard Biesheuvel" <ard.biesheuvel@arm.com>]

On 10/16/20 3:36 AM, Fu, Siyuan wrote:
> Hi, Sami
> 
> I know the traditional MM is planned to be deprecated but the reality is that there
> are many existing traditional MM platforms/drivers and the migration has to happen
> step-by-step. It may take a long time like several years, not days or months. Not sure
> if we really want to maintain duplicate code in 3 different MM cores in EDK2 for
> such a long time.
> 

Could you explain more about the gap that needs to be bridged here? I 
suppose the desire is to be able to reuse existing DXE_SMM_DRIVER 
modules, and deploy them unmodified in a standalone MM context?

So would you expect runtime dispatch for these drivers? What about any 
accesses to EFI boot services, which are no longer possible when running 
under standalone MM? Do you have any reason to believe that this hybrid 
MM core will be able to run a significant fraction of those existing 
drivers?

> Would you think it's acceptable if we put the traditional MM related code controlled
> by a feature flag PCD in StandaloneMmPkg core? The default value of the PCD can
> be set as disabled so those existing platforms doesn't need to be changed.
> 

This is security critical code, and having PCD controlled behavior like 
this makes it much hard to reason about correctness in all its 
instantiation. I guess I would have to see what the code looks like, but 
having PCD checks all over the place does not seem like a great way to 
do this IMHO.

-- 
Ard.