OvmfPkg/BdsPlatform: don't restore NvVars from disk when flash is present

QemuFlashFvbServicesRuntimeDxe provides actual persistent storage for
non-volatile variables. When it is active, any on-disk NvVars file counts
as a stale source of variables -- hence don't load these files in BDS.

This also allows Secure Boot settings (eg. enrolled keys) to survive cold
VM reboots.

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@14844 6f19259b-4bc3-4df7-8a09-765794883524

OvmfPkg/Library/PlatformBdsLib/BdsPlatform.c

@@ -1073,11 +1073,16 @@ Returns:
 
   ConnectRootBridge ();
 
-  //
-  // Try to restore variables from the hard disk early so
-  // they can be used for the other BDS connect operations.
-  //
-  PlatformBdsRestoreNvVarsFromHardDisk ();
+  if (PcdGetBool (PcdOvmfFlashVariablesEnable)) {
+    DEBUG ((EFI_D_INFO, "PlatformBdsPolicyBehavior: not restoring NvVars "
+      "from disk since flash variables appear to be supported.\n"));
+  } else {
+    //
+    // Try to restore variables from the hard disk early so
+    // they can be used for the other BDS connect operations.
+    //
+    PlatformBdsRestoreNvVarsFromHardDisk ();
+  }
 
   //
   // Init the time out value

OvmfPkg/Library/PlatformBdsLib/PlatformBdsLib.inf

@@ -57,6 +57,7 @@
   gEfiIntelFrameworkModulePkgTokenSpaceGuid.PcdPlatformBootTimeOut
   gEfiIntelFrameworkModulePkgTokenSpaceGuid.PcdLogoFile
   gUefiOvmfPkgTokenSpaceGuid.PcdEmuVariableEvent
+  gUefiOvmfPkgTokenSpaceGuid.PcdOvmfFlashVariablesEnable
 
 [Pcd.IA32, Pcd.X64]
   gEfiMdePkgTokenSpaceGuid.PcdFSBClock