OvmfPkg: PlatformBdsLib: signal End-of-Dxe event group

(Paraphrasing git commit 9cd7d3c5 / SVN r17713:)

Currently, OvmfPkg fails to signal the End-of-Dxe event group when
entering the BDS phase, which results in some loss of functionality, eg.
variable reclaim in the variable driver, and the memory region splitting
in the DXE core that belongs to the properties table feature specified in
UEFI-2.5.

As discussed on the edk2-devel mailing list here:

http://thread.gmane.org/gmane.comp.bios.tianocore.devel/16088/focus=16109

it is up to the platform BDS to signal End-of-Dxe, since there may be
platform specific ordering constraints with respect to the signalling of
the event that are difficult to honor at the generic level.

(OvmfPkg specifics:)

(1) In OvmfPkg, we can't signal End-of-Dxe before PCI enumeration
    completes. According to the previous patch, that would trigger
    OvmfPkg/AcpiS3SaveDxe to save S3 state *before* the following chain of
    action happened:

    - PCI enumeration completes
    - ACPI tables are installed by OvmfPkg/AcpiPlatformDxe
    - the FACS table becomes available

    Since OvmfPkg/AcpiS3SaveDxe can only save S3 state once the FACS table
    is available, we must delay the End-of-Dxe signal until after PCI
    enumeration completes (ie. root bridges are connected).

(2) Pre-patch, S3Ready() in OvmfPkg/AcpiS3SaveDxe is entered from
    BdsLibBootViaBootOption()
    [IntelFrameworkModulePkg/Library/GenericBdsLib/BdsBoot.c].

    After the patch, we enter S3Ready() earlier than that, by signaling
    End-of-Dxe in PlatformBdsPolicyBehavior(). The timing / location of
    this new call is correct as well, and the original call (that now
    becomes the chronologically second call) becomes a no-op: S3Ready() is
    protected against 2nd and later entries.

Cc: Jordan Justen <jordan.l.justen@intel.com>
Contributed-under: TianoCore Contribution Agreement 1.0
Signed-off-by: Laszlo Ersek <lersek@redhat.com>
Reviewed-by: Jordan Justen <jordan.l.justen@intel.com>

git-svn-id: https://svn.code.sf.net/p/edk2/code/trunk/edk2@18035 6f19259b-4bc3-4df7-8a09-765794883524

OvmfPkg/Library/PlatformBdsLib/BdsPlatform.c

@@ -1163,6 +1163,27 @@ Returns:
 }
 
 
+/**
+  Empty callback function executed when the EndOfDxe event group is signaled.
+
+  We only need this function because we'd like to signal EndOfDxe, and for that
+  we need to create an event, with a callback function.
+
+  @param[in] Event    Event whose notification function is being invoked.
+  @param[in] Context  The pointer to the notification function's context, which
+                      is implementation-dependent.
+**/
+STATIC
+VOID
+EFIAPI
+OnEndOfDxe (
+  IN EFI_EVENT Event,
+  IN VOID      *Context
+  )
+{
+}
+
+
 VOID
 EFIAPI
 PlatformBdsPolicyBehavior (
@@ -1197,12 +1218,28 @@ Returns:
 {
   EFI_STATUS                         Status;
   EFI_BOOT_MODE                      BootMode;
+  EFI_EVENT                          EndOfDxeEvent;
 
   DEBUG ((EFI_D_INFO, "PlatformBdsPolicyBehavior\n"));
 
   VisitAllInstancesOfProtocol (&gEfiPciRootBridgeIoProtocolGuid,
     ConnectRootBridge, NULL);
 
+  //
+  // We can't signal End-of-Dxe earlier than this. Namely, End-of-Dxe triggers
+  // the preparation of S3 system information. That logic has a hard dependency
+  // on the presence of the FACS ACPI table. Since our ACPI tables are only
+  // installed after PCI enumeration completes, we must not trigger the S3 save
+  // earlier, hence we can't signal End-of-Dxe earlier.
+  //
+  Status = gBS->CreateEventEx (EVT_NOTIFY_SIGNAL, TPL_CALLBACK, OnEndOfDxe,
+                  NULL /* NotifyContext */, &gEfiEndOfDxeEventGroupGuid,
+                  &EndOfDxeEvent);
+  if (!EFI_ERROR (Status)) {
+    gBS->SignalEvent (EndOfDxeEvent);
+    gBS->CloseEvent (EndOfDxeEvent);
+  }
+
   if (PcdGetBool (PcdOvmfFlashVariablesEnable)) {
     DEBUG ((EFI_D_INFO, "PlatformBdsPolicyBehavior: not restoring NvVars "
       "from disk since flash variables appear to be supported.\n"));

OvmfPkg/Library/PlatformBdsLib/BdsPlatform.h

@@ -59,6 +59,7 @@ Abstract:
 #include <Guid/Mps.h>
 #include <Guid/HobList.h>
 #include <Guid/GlobalVariable.h>
+#include <Guid/EventGroup.h>
 
 #include <OvmfPlatforms.h>
 

OvmfPkg/Library/PlatformBdsLib/PlatformBdsLib.inf

@@ -65,3 +65,6 @@
 [Protocols]
   gEfiDecompressProtocolGuid
   gEfiPciRootBridgeIoProtocolGuid
+
+[Guids]
+  gEfiEndOfDxeEventGroupGuid