MdeModulePkg/VariableRuntimeDxe: implement standalone MM version

Reuse most of the existing code to implement a variable runtime
driver that will be able to execute in the context of standalone
MM.

Contributed-under: TianoCore Contribution Agreement 1.1
Signed-off-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Reviewed-by: Jian J Wang <jian.j.wang@intel.com>
Reviewed-by: Star Zeng <star.zeng@intel.com>

MdeModulePkg/Universal/Variable/RuntimeDxe/VariableStandaloneMm.c

@@ -0,0 +1,95 @@
+/** @file
+
+  Parts of the SMM/MM implementation that are specific to standalone MM
+
+Copyright (c) 2011 - 2018, Intel Corporation. All rights reserved. <BR>
+Copyright (c) 2018, Linaro, Ltd. All rights reserved. <BR>
+This program and the accompanying materials
+are licensed and made available under the terms and conditions of the BSD License
+which accompanies this distribution.  The full text of the license may be found at
+http://opensource.org/licenses/bsd-license.php
+
+THE PROGRAM IS DISTRIBUTED UNDER THE BSD LICENSE ON AN "AS IS" BASIS,
+WITHOUT WARRANTIES OR REPRESENTATIONS OF ANY KIND, EITHER EXPRESS OR IMPLIED.
+
+**/
+
+#include "Variable.h"
+
+/**
+  This function checks if the buffer is valid per processor architecture and
+  does not overlap with SMRAM.
+
+  @param Buffer The buffer start address to be checked.
+  @param Length The buffer length to be checked.
+
+  @retval TRUE  This buffer is valid per processor architecture and does not
+                overlap with SMRAM.
+  @retval FALSE This buffer is not valid per processor architecture or overlaps
+                with SMRAM.
+**/
+BOOLEAN
+VariableSmmIsBufferOutsideSmmValid (
+  IN EFI_PHYSICAL_ADDRESS  Buffer,
+  IN UINT64                Length
+  )
+{
+  return TRUE;
+}
+
+/**
+  Notify the system that the SMM variable driver is ready
+**/
+VOID
+VariableNotifySmmReady (
+  VOID
+  )
+{
+}
+
+/**
+  Notify the system that the SMM variable write driver is ready
+**/
+VOID
+VariableNotifySmmWriteReady (
+  VOID
+  )
+{
+}
+
+/**
+  Variable service MM driver entry point
+
+  @param[in] ImageHandle    A handle for the image that is initializing this
+                            driver
+  @param[in] MmSystemTable  A pointer to the MM system table
+
+  @retval EFI_SUCCESS       Variable service successfully initialized.
+**/
+EFI_STATUS
+EFIAPI
+VariableServiceInitialize (
+  IN EFI_HANDLE                           ImageHandle,
+  IN EFI_MM_SYSTEM_TABLE                  *MmSystemTable
+  )
+{
+  return MmVariableServiceInitialize ();
+}
+
+/**
+  Whether the TCG or TCG2 protocols are installed in the UEFI protocol database.
+  This information is used by the MorLock code to infer whether an existing
+  MOR variable is legitimate or not.
+
+  @retval TRUE  Either the TCG or TCG2 protocol is installed in the UEFI
+                protocol database
+  @retval FALSE Neither the TCG nor the TCG2 protocol is installed in the UEFI
+                protocol database
+**/
+BOOLEAN
+VariableHaveTcgProtocols (
+  VOID
+  )
+{
+  return FALSE;
+}