Re: [PATCH v2 04/11] MdePkg/Include: Add StandaloneMmServicesTableLib library

[Laszlo Ersek <lersek@redhat.com>]

On 01/03/19 12:03, Ard Biesheuvel wrote:
> On Wed, 2 Jan 2019 at 14:14, Jagadeesh Ujja <jagadeesh.ujja@arm.com> wrote:
>>
>> Some of the existing DXE drivers can be refactored to execute within
>> the Standalone MM execution environment as well. Allow such drivers to
>> get access to the Standalone MM services tables.
>>
>> Add a mechanism to determine the execution mode is required.
>> i.e, in MM or non-MM
>>
>> Contributed-under: TianoCore Contribution Agreement 1.1
>> Signed-off-by: Jagadeesh Ujja <jagadeesh.ujja@arm.com>
>> ---
>>  MdePkg/Include/Library/StandaloneMmServicesTableLib.h                        | 43 ++++++++++++++++++++
>>  MdePkg/Library/StandaloneMmServicesTableLib/StandaloneMmServicesTableLib.c   | 39 ++++++++++++++++++
>>  MdePkg/Library/StandaloneMmServicesTableLib/StandaloneMmServicesTableLib.inf | 36 ++++++++++++++++
>>  MdePkg/MdePkg.dec                                                            |  4 ++
>>  4 files changed, 122 insertions(+)
>>
> 
> OK, so since the PI spec only refers to MM mode now, this library
> class should be
> 
> MmServicesTableLib|Include/Library/MmServicesTableLib.h
> 
> with an implementation in MdeModulePkg that exposes the deprecated SMM
> system table as the MM system table.
> 
> In StandaloneMmPkg, we can add an implementation that exposes the
> standalone MM system table.
> 
> (They are binary compatible, so it is just a matter of casting one
> pointer to the other)
> 
> With this in place, we can go ahead and update FaultTolerantWrite and
> Variable SMM driver to switch from SmmServicesTableLib to
> MmServicesTableLib. This will require existing x86 platforms to define
> a new library class resolution for MmServicesTableLib, referring to
> the implementation in MdeModulePkg. This is unfortunate, but it is an
> unavoidable consequence of the PI spec changes.

It shouldn't be too intrusive or hard to review, I expect.

> 
> Remaining question is what to do with InSmm() ...

I'm lacking the context on this; on the other hand, I can refer back to
at least one earlier discussion -- there had been multiple -- of the
discrepancy between the PI spec and the edk2 code. See:

- bullet (9) in
<http://mid.mail-archive.com/aada511c-bdb9-d833-caa5-bee56cc47d27@redhat.com>,
- and
<http://mid.mail-archive.com/0C09AFA07DD0434D9E2A0C6AEB0483103BB55B46@shsmsx102.ccr.corp.intel.com>.

Not sure how that can be applied to Arm.

Thanks
Laszlo