Months ago, I sent patch set to fix potential issues in the usage of SMI handler unregistering SMI handler. Discussion can be found in below
link:
https://edk2.groups.io/g/devel/topic/103925794#114251

The conclusion was to only support SMI handler unregistering itself, and not allow  SMI handler unregistering other handlers, because we thought there would be no such usage.
However, recently, I find in some platform, there is kind of usage.
To also support SMI handler unregistering other handlers, this patch set use a totally different design. So I revert the former ones first to make the code more readable.

Thank Laszlo for bring up the initial idea for the new design.

V2&V3:
Code refine based on Ray's comments

Zhiguang Liu (6):
  Revert 2ec8f0c6407f062441b205b900038933865c7b3c
  Revert 049ff6c39c73edd3709c05bd0e46184320471358
  Revert 17b28722008eab745ce186b72cd325944cbe6bf0
  Revert ae1079b386a597108a8070652bf7cdaa4ec3dda3
  MdeModulePkg/SMM: Support to unregister SMI handler in SMI handlers
  StandaloneMmPkg: Support to unregister MMI handler in MMI handlers

 MdeModulePkg/Core/PiSmmCore/PiSmmCore.h |   1 +
 MdeModulePkg/Core/PiSmmCore/Smi.c       | 198 ++++++++++++++++-------
 StandaloneMmPkg/Core/Mmi.c              | 200 +++++++++++++++++-------
 3 files changed, 292 insertions(+), 107 deletions(-)

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2.31.1.windows.1