MdeModulePkg: Notify BeforeExitBootServices in CoreExitBootServices

Location of notification is has been specified in UEFI v2.9.

Cc: Gerd Hoffmann <kraxel@redhat.com>
Cc: James Bottomley <jejb@linux.ibm.com>
Cc: Jiewen Yao <jiewen.yao@intel.com>
Cc: Tom Lendacky <thomas.lendacky@amd.com>
Cc: Ard Biesheuvel <ardb@kernel.org>
Cc: "Min M. Xu" <min.m.xu@intel.com>
Cc: Andrew Fish <afish@apple.com>
Cc: "Michael D. Kinney" <michael.d.kinney@intel.com>
Cc: Ray Ni <ray.ni@intel.com>

Acked-by: Jiewen Yao <Jiewen.yao@intel.com>
Reviewed-by: Michael D Kinney <michael.d.kinney@intel.com>
Signed-off-by: Dionna Glaze <dionnaglaze@google.com>
Message-Id: <20221108164616.3251967-4-dionnaglaze@google.com>

MdeModulePkg/Core/Dxe/DxeMain.inf

@@ -100,6 +100,7 @@
   gEfiEventVirtualAddressChangeGuid             ## CONSUMES             ## Event
   ## CONSUMES   ## Event
   ## PRODUCES   ## Event
+  gEfiEventBeforeExitBootServicesGuid
   gEfiEventExitBootServicesGuid
   gEfiHobMemoryAllocModuleGuid                  ## SOMETIMES_CONSUMES   ## HOB
   gEfiFirmwareFileSystem2Guid                   ## CONSUMES             ## GUID # Used to compare with FV's file system guid and get the FV's file system format

MdeModulePkg/Core/Dxe/DxeMain/DxeMain.c

@@ -763,6 +763,12 @@ CoreExitBootServices (
 {
   EFI_STATUS  Status;
 
+  //
+  // Notify other drivers of their last chance to use boot services
+  // before the memory map is terminated.
+  //
+  CoreNotifySignalList (&gEfiEventBeforeExitBootServicesGuid);
+
   //
   // Disable Timer
   //