Re: [PATCH V2 08/15] MdeModulePkg Variable: Add emulated variable NV mode support

["Wang, Jian J" <jian.j.wang@intel.com>]

Hi Star,

Just two minor comments below.

> -----Original Message-----
> From: Zeng, Star
> Sent: Monday, January 14, 2019 11:20 PM
> To: edk2-devel@lists.01.org
> Cc: Zeng, Star <star.zeng@intel.com>; Wang, Jian J <jian.j.wang@intel.com>;
> Wu, Hao A <hao.a.wu@intel.com>; Kinney, Michael D
> <michael.d.kinney@intel.com>; Gao, Liming <liming.gao@intel.com>; Ni, Ray
> <ray.ni@intel.com>; Laszlo Ersek <lersek@redhat.com>; Ard Biesheuvel
> <ard.biesheuvel@linaro.org>
> Subject: [PATCH V2 08/15] MdeModulePkg Variable: Add emulated variable NV
> mode support
> 
> REF: https://bugzilla.tianocore.org/show_bug.cgi?id=1323
> Merge EmuVariable and Real variable driver.
> 
> Add emulated variable NV mode support in real variable driver.
> Platform can configure PcdEmuVariableNvModeEnable statically
> (build time) or dynamically (boot time) to support emulated
> variable NV mode.
> 

It would be better to mention, although it could be dynamically
configured, it's just a one-shot action before this driver is loaded,
just in case of any misunderstanding. 

> Then EmuVariableRuntimeDxe could be removed, the removal of
> EmuVariableRuntimeDxe will be done after platforms are migrated
> to use the merged variable driver.
> 
> Cc: Jian J Wang <jian.j.wang@intel.com>
> Cc: Hao Wu <hao.a.wu@intel.com>
> Cc: Michael D Kinney <michael.d.kinney@intel.com>
> Cc: Liming Gao <liming.gao@intel.com>
> Cc: Ray Ni <ray.ni@intel.com>
> Cc: Laszlo Ersek <lersek@redhat.com>
> Cc: Ard Biesheuvel <ard.biesheuvel@linaro.org>
> Contributed-under: TianoCore Contribution Agreement 1.1
> Signed-off-by: Star Zeng <star.zeng@intel.com>
> ---
>  .../Universal/Variable/RuntimeDxe/Variable.c       | 318 +++++++++++++++------
>  .../Universal/Variable/RuntimeDxe/Variable.h       |   1 +
>  .../Universal/Variable/RuntimeDxe/VariableDxe.c    |  27 +-
>  .../Variable/RuntimeDxe/VariableRuntimeDxe.inf     |   4 +-
>  .../Universal/Variable/RuntimeDxe/VariableSmm.c    |  29 +-
>  .../Universal/Variable/RuntimeDxe/VariableSmm.inf  |   4 +-
>  6 files changed, 271 insertions(+), 112 deletions(-)
> 
> diff --git a/MdeModulePkg/Universal/Variable/RuntimeDxe/Variable.c
> b/MdeModulePkg/Universal/Variable/RuntimeDxe/Variable.c
> index 4c8e1d8cf4f1..845276d891ae 100644
> --- a/MdeModulePkg/Universal/Variable/RuntimeDxe/Variable.c
> +++ b/MdeModulePkg/Universal/Variable/RuntimeDxe/Variable.c
> @@ -34,6 +34,7 @@ VARIABLE_MODULE_GLOBAL  *mVariableModuleGlobal;
> 
>  ///
>  /// Define a memory cache that improves the search performance for a variable.
> +/// For EmuNvMode == TRUE, it will be equal to NonVolatileVariableBase.
>  ///
>  VARIABLE_STORE_HEADER  *mNvVariableCache      = NULL;
> 
> @@ -273,7 +274,7 @@ UpdateVariableStore (
>    //
>    // Check if the Data is Volatile.
>    //
> -  if (!Volatile) {
> +  if (!Volatile && !mVariableModuleGlobal->VariableGlobal.EmuNvMode) {
>      if (Fvb == NULL) {
>        return EFI_UNSUPPORTED;
>      }
> @@ -296,17 +297,30 @@ UpdateVariableStore (
>      // Data Pointer should point to the actual Address where data is to be
>      // written.
>      //
> -    VolatileBase = (VARIABLE_STORE_HEADER *) ((UINTN)
> mVariableModuleGlobal->VariableGlobal.VolatileVariableBase);
> -    if (SetByIndex) {
> -      DataPtr += mVariableModuleGlobal->VariableGlobal.VolatileVariableBase;
> -    }
> +    if (Volatile) {
> +      VolatileBase = (VARIABLE_STORE_HEADER *) ((UINTN)
> mVariableModuleGlobal->VariableGlobal.VolatileVariableBase);
> +      if (SetByIndex) {
> +        DataPtr += mVariableModuleGlobal->VariableGlobal.VolatileVariableBase;
> +      }
> 
> -    if ((DataPtr + DataSize) > ((UINTN) VolatileBase + VolatileBase->Size)) {
> -      return EFI_OUT_OF_RESOURCES;
> +      if ((DataPtr + DataSize) > ((UINTN) VolatileBase + VolatileBase->Size)) {
> +        return EFI_OUT_OF_RESOURCES;
> +      }
> +    } else {
> +      //
> +      // Emulated non-volatile variable mode.
> +      //
> +      if (SetByIndex) {
> +        DataPtr += (UINTN) mNvVariableCache;
> +      }
> +
> +      if ((DataPtr + DataSize) > ((UINTN) mNvVariableCache + mNvVariableCache-
> >Size)) {
> +        return EFI_OUT_OF_RESOURCES;
> +      }
>      }
> 
>      //
> -    // If Volatile Variable just do a simple mem copy.
> +    // If Volatile/Emulated Non-volatile Variable just do a simple mem copy.
>      //
>      CopyMem ((UINT8 *)(UINTN)DataPtr, Buffer, DataSize);
>      return EFI_SUCCESS;
> @@ -987,7 +1001,7 @@ Reclaim (
>    CommonUserVariableTotalSize = 0;
>    HwErrVariableTotalSize  = 0;
> 
> -  if (IsVolatile) {
> +  if (IsVolatile || mVariableModuleGlobal->VariableGlobal.EmuNvMode) {
>      //
>      // Start Pointers for the variable.
>      //
> @@ -1155,13 +1169,21 @@ Reclaim (
>      CurrPtr += NewVariableSize;
>    }
> 
> -  if (IsVolatile) {
> +  if (IsVolatile || mVariableModuleGlobal->VariableGlobal.EmuNvMode) {
>      //
> -    // If volatile variable store, just copy valid buffer.
> +    // If volatile/emulated non-volatile variable store, just copy valid buffer.
>      //
>      SetMem ((UINT8 *) (UINTN) VariableBase, VariableStoreHeader->Size, 0xff);
>      CopyMem ((UINT8 *) (UINTN) VariableBase, ValidBuffer, (UINTN) CurrPtr -
> (UINTN) ValidBuffer);
>      *LastVariableOffset = (UINTN) CurrPtr - (UINTN) ValidBuffer;
> +    if (!IsVolatile) {
> +      //
> +      // Emulated non-volatile variable mode.
> +      //
> +      mVariableModuleGlobal->HwErrVariableTotalSize = HwErrVariableTotalSize;
> +      mVariableModuleGlobal->CommonVariableTotalSize =
> CommonVariableTotalSize;
> +      mVariableModuleGlobal->CommonUserVariableTotalSize =
> CommonUserVariableTotalSize;
> +    }
>      Status  = EFI_SUCCESS;
>    } else {
>      //
> @@ -1200,7 +1222,7 @@ Reclaim (
>    }
> 
>  Done:
> -  if (IsVolatile) {
> +  if (IsVolatile || mVariableModuleGlobal->VariableGlobal.EmuNvMode) {
>      FreePool (ValidBuffer);
>    } else {
>      //
> @@ -2147,7 +2169,7 @@ UpdateVariable (
>    BOOLEAN                             IsCommonUserVariable;
>    AUTHENTICATED_VARIABLE_HEADER       *AuthVariable;
> 
> -  if (mVariableModuleGlobal->FvbInstance == NULL) {
> +  if (mVariableModuleGlobal->FvbInstance == NULL
> && !mVariableModuleGlobal->VariableGlobal.EmuNvMode) {
>      //
>      // The FVB protocol is not ready, so the
> EFI_VARIABLE_WRITE_ARCH_PROTOCOL is not installed.
>      //
> @@ -2566,85 +2588,106 @@ UpdateVariable (
>        }
>        goto Done;
>      }
> -    //
> -    // Four steps
> -    // 1. Write variable header
> -    // 2. Set variable state to header valid
> -    // 3. Write variable data
> -    // 4. Set variable state to valid
> -    //
> -    //
> -    // Step 1:
> -    //
> -    Status = UpdateVariableStore (
> -               &mVariableModuleGlobal->VariableGlobal,
> -               FALSE,
> -               TRUE,
> -               Fvb,
> -               mVariableModuleGlobal->NonVolatileLastVariableOffset,
> -               (UINT32) GetVariableHeaderSize (),
> -               (UINT8 *) NextVariable
> -               );
> 
> -    if (EFI_ERROR (Status)) {
> -      goto Done;
> -    }
> +    if (!mVariableModuleGlobal->VariableGlobal.EmuNvMode) {
> +      //
> +      // Four steps
> +      // 1. Write variable header
> +      // 2. Set variable state to header valid
> +      // 3. Write variable data
> +      // 4. Set variable state to valid
> +      //
> +      //
> +      // Step 1:
> +      //
> +      Status = UpdateVariableStore (
> +                 &mVariableModuleGlobal->VariableGlobal,
> +                 FALSE,
> +                 TRUE,
> +                 Fvb,
> +                 mVariableModuleGlobal->NonVolatileLastVariableOffset,
> +                 (UINT32) GetVariableHeaderSize (),
> +                 (UINT8 *) NextVariable
> +                 );
> 
> -    //
> -    // Step 2:
> -    //
> -    NextVariable->State = VAR_HEADER_VALID_ONLY;
> -    Status = UpdateVariableStore (
> -               &mVariableModuleGlobal->VariableGlobal,
> -               FALSE,
> -               TRUE,
> -               Fvb,
> -               mVariableModuleGlobal->NonVolatileLastVariableOffset + OFFSET_OF
> (VARIABLE_HEADER, State),
> -               sizeof (UINT8),
> -               &NextVariable->State
> -               );
> +      if (EFI_ERROR (Status)) {
> +        goto Done;
> +      }
> 
> -    if (EFI_ERROR (Status)) {
> -      goto Done;
> -    }
> -    //
> -    // Step 3:
> -    //
> -    Status = UpdateVariableStore (
> -               &mVariableModuleGlobal->VariableGlobal,
> -               FALSE,
> -               TRUE,
> -               Fvb,
> -               mVariableModuleGlobal->NonVolatileLastVariableOffset +
> GetVariableHeaderSize (),
> -               (UINT32) (VarSize - GetVariableHeaderSize ()),
> -               (UINT8 *) NextVariable + GetVariableHeaderSize ()
> -               );
> +      //
> +      // Step 2:
> +      //
> +      NextVariable->State = VAR_HEADER_VALID_ONLY;
> +      Status = UpdateVariableStore (
> +                 &mVariableModuleGlobal->VariableGlobal,
> +                 FALSE,
> +                 TRUE,
> +                 Fvb,
> +                 mVariableModuleGlobal->NonVolatileLastVariableOffset +
> OFFSET_OF (VARIABLE_HEADER, State),
> +                 sizeof (UINT8),
> +                 &NextVariable->State
> +                 );
> 
> -    if (EFI_ERROR (Status)) {
> -      goto Done;
> -    }
> -    //
> -    // Step 4:
> -    //
> -    NextVariable->State = VAR_ADDED;
> -    Status = UpdateVariableStore (
> -               &mVariableModuleGlobal->VariableGlobal,
> -               FALSE,
> -               TRUE,
> -               Fvb,
> -               mVariableModuleGlobal->NonVolatileLastVariableOffset + OFFSET_OF
> (VARIABLE_HEADER, State),
> -               sizeof (UINT8),
> -               &NextVariable->State
> -               );
> +      if (EFI_ERROR (Status)) {
> +        goto Done;
> +      }
> +      //
> +      // Step 3:
> +      //
> +      Status = UpdateVariableStore (
> +                 &mVariableModuleGlobal->VariableGlobal,
> +                 FALSE,
> +                 TRUE,
> +                 Fvb,
> +                 mVariableModuleGlobal->NonVolatileLastVariableOffset +
> GetVariableHeaderSize (),
> +                 (UINT32) (VarSize - GetVariableHeaderSize ()),
> +                 (UINT8 *) NextVariable + GetVariableHeaderSize ()
> +                 );
> 
> -    if (EFI_ERROR (Status)) {
> -      goto Done;
> -    }
> +      if (EFI_ERROR (Status)) {
> +        goto Done;
> +      }
> +      //
> +      // Step 4:
> +      //
> +      NextVariable->State = VAR_ADDED;
> +      Status = UpdateVariableStore (
> +                 &mVariableModuleGlobal->VariableGlobal,
> +                 FALSE,
> +                 TRUE,
> +                 Fvb,
> +                 mVariableModuleGlobal->NonVolatileLastVariableOffset +
> OFFSET_OF (VARIABLE_HEADER, State),
> +                 sizeof (UINT8),
> +                 &NextVariable->State
> +                 );
> 
> -    //
> -    // update the memory copy of Flash region.
> -    //
> -    CopyMem ((UINT8 *)mNvVariableCache + mVariableModuleGlobal-
> >NonVolatileLastVariableOffset, (UINT8 *)NextVariable, VarSize);
> +      if (EFI_ERROR (Status)) {
> +        goto Done;
> +      }
> +
> +      //
> +      // update the memory copy of Flash region.
> +      //
> +      CopyMem ((UINT8 *)mNvVariableCache + mVariableModuleGlobal-
> >NonVolatileLastVariableOffset, (UINT8 *)NextVariable, VarSize);
> +    } else {
> +      //
> +      // Emulated non-volatile variable mode.
> +      //
> +      NextVariable->State = VAR_ADDED;
> +      Status = UpdateVariableStore (
> +                 &mVariableModuleGlobal->VariableGlobal,
> +                 FALSE,
> +                 TRUE,
> +                 Fvb,
> +                 mVariableModuleGlobal->NonVolatileLastVariableOffset,
> +                 (UINT32) VarSize,
> +                 (UINT8 *) NextVariable
> +                 );
> +
> +      if (EFI_ERROR (Status)) {
> +        goto Done;
> +      }
> +    }
> 
>      mVariableModuleGlobal->NonVolatileLastVariableOffset += HEADER_ALIGN
> (VarSize);
> 
> @@ -3876,6 +3919,93 @@ InitRealNonVolatileVariableStore (
>  }
> 
>  /**
> +  Init emulated non-volatile variable store.
> +
> +  @param[out] VariableStoreBase Output pointer to emulated non-volatile
> variable store base.
> +
> +  @retval EFI_SUCCESS           Function successfully executed.
> +  @retval EFI_OUT_OF_RESOURCES  Fail to allocate enough memory resource.
> +
> +**/
> +EFI_STATUS
> +InitEmuNonVolatileVariableStore (
> +  EFI_PHYSICAL_ADDRESS  *VariableStoreBase
> +  )
> +{
> +  VARIABLE_STORE_HEADER *VariableStore;
> +  UINT32                VariableStoreLength;
> +  BOOLEAN               FullyInitializeStore;
> +  UINT32                HwErrStorageSize;
> +
> +  FullyInitializeStore = TRUE;
> +
> +  VariableStoreLength = PcdGet32 (PcdVariableStoreSize);
> +  ASSERT (sizeof (VARIABLE_STORE_HEADER) <= VariableStoreLength);
> +
> +  //
> +  // Allocate memory for variable store.
> +  //
> +  if (PcdGet64 (PcdEmuVariableNvStoreReserved) == 0) {
> +    VariableStore = (VARIABLE_STORE_HEADER *) AllocateRuntimePool
> (VariableStoreLength);
> +    if (VariableStore == NULL) {
> +      return EFI_OUT_OF_RESOURCES;
> +    }
> +  } else {
> +    //
> +    // A memory location has been reserved for the NV variable store.  Certain
> +    // platforms may be able to preserve a memory range across system resets,
> +    // thereby providing better NV variable emulation.
> +    //
> +    VariableStore =
> +      (VARIABLE_STORE_HEADER *)(VOID*)(UINTN)
> +        PcdGet64 (PcdEmuVariableNvStoreReserved);
> +    if ((VariableStore->Size == VariableStoreLength) &&
> +        (CompareGuid (&VariableStore->Signature,
> &gEfiAuthenticatedVariableGuid) ||
> +         CompareGuid (&VariableStore->Signature, &gEfiVariableGuid)) &&
> +        (VariableStore->Format == VARIABLE_STORE_FORMATTED) &&
> +        (VariableStore->State == VARIABLE_STORE_HEALTHY)) {
> +      DEBUG((
> +        DEBUG_INFO,
> +        "Variable Store reserved at %p appears to be valid\n",
> +        VariableStore
> +        ));
> +      FullyInitializeStore = FALSE;
> +    }
> +  }
> +
> +  if (FullyInitializeStore) {
> +    SetMem (VariableStore, VariableStoreLength, 0xff);
> +    //
> +    // Use gEfiAuthenticatedVariableGuid for potential auth variable support.
> +    //
> +    CopyGuid (&VariableStore->Signature, &gEfiAuthenticatedVariableGuid);
> +    VariableStore->Size       = VariableStoreLength;
> +    VariableStore->Format     = VARIABLE_STORE_FORMATTED;
> +    VariableStore->State      = VARIABLE_STORE_HEALTHY;
> +    VariableStore->Reserved   = 0;
> +    VariableStore->Reserved1  = 0;
> +  }
> +
> +  *VariableStoreBase = (EFI_PHYSICAL_ADDRESS) (UINTN) VariableStore;
> +
> +  HwErrStorageSize = PcdGet32 (PcdHwErrStorageSize);
> +
> +  //
> +  // Note that in EdkII variable driver implementation, Hardware Error Record
> type variable
> +  // is stored with common variable in the same NV region. So the platform
> integrator should
> +  // ensure that the value of PcdHwErrStorageSize is less than the value of
> +  // (VariableStoreLength - sizeof (VARIABLE_STORE_HEADER)).
> +  //
> +  ASSERT (HwErrStorageSize < (VariableStoreLength - sizeof
> (VARIABLE_STORE_HEADER)));
> +
> +  mVariableModuleGlobal->CommonVariableSpace = ((UINTN)
> VariableStoreLength - sizeof (VARIABLE_STORE_HEADER) - HwErrStorageSize);
> +  mVariableModuleGlobal->CommonMaxUserVariableSpace =
> mVariableModuleGlobal->CommonVariableSpace;
> +  mVariableModuleGlobal->CommonRuntimeVariableSpace =
> mVariableModuleGlobal->CommonVariableSpace;
> +
> +  return EFI_SUCCESS;
> +}
> +
> +/**
>    Init non-volatile variable store.
> 
>    @retval EFI_SUCCESS           Function successfully executed.
> @@ -3894,9 +4024,19 @@ InitNonVolatileVariableStore (
>    UINTN                                 VariableSize;
>    EFI_STATUS                            Status;
> 
> -  Status = InitRealNonVolatileVariableStore (&VariableStoreBase);
> -  if (EFI_ERROR (Status)) {
> -    return Status;
> +  if (!PcdGetBool (PcdEmuVariableNvModeEnable)) {
> +    Status = InitRealNonVolatileVariableStore (&VariableStoreBase);
> +    if (EFI_ERROR (Status)) {
> +      return Status;
> +    }
> +    mVariableModuleGlobal->VariableGlobal.EmuNvMode = FALSE;
> +  } else {
> +    Status = InitEmuNonVolatileVariableStore (&VariableStoreBase);
> +    if (EFI_ERROR (Status)) {
> +      return Status;
> +    }
> +    mVariableModuleGlobal->VariableGlobal.EmuNvMode = TRUE;
> +    DEBUG ((DEBUG_INFO, "Variable driver will work at emulated non-volatile
> variable mode!\n"));
>    }
> 

The logic is not wrong, just the if/else style might cause confusion at
the first glance. Swapping the if/else might let the code more clear.

if (PcdGetBool (PcdEmuVariableNvModeEnable)) {
   ...initialize emulated variable store...
} else {
   ...initialize the real nv variable store...
}

>    mVariableModuleGlobal->VariableGlobal.NonVolatileVariableBase =
> VariableStoreBase;
> diff --git a/MdeModulePkg/Universal/Variable/RuntimeDxe/Variable.h
> b/MdeModulePkg/Universal/Variable/RuntimeDxe/Variable.h
> index 566e7268d187..fdc92b2b017c 100644
> --- a/MdeModulePkg/Universal/Variable/RuntimeDxe/Variable.h
> +++ b/MdeModulePkg/Universal/Variable/RuntimeDxe/Variable.h
> @@ -92,6 +92,7 @@ typedef struct {
>    UINT32                ReentrantState;
>    BOOLEAN               AuthFormat;
>    BOOLEAN               AuthSupport;
> +  BOOLEAN               EmuNvMode;
>  } VARIABLE_GLOBAL;
> 
>  typedef struct {
> diff --git a/MdeModulePkg/Universal/Variable/RuntimeDxe/VariableDxe.c
> b/MdeModulePkg/Universal/Variable/RuntimeDxe/VariableDxe.c
> index 5131e6f351e4..7d5c8b3f842d 100644
> --- a/MdeModulePkg/Universal/Variable/RuntimeDxe/VariableDxe.c
> +++ b/MdeModulePkg/Universal/Variable/RuntimeDxe/VariableDxe.c
> @@ -533,16 +533,23 @@ VariableServiceInitialize (
>                    );
>    ASSERT_EFI_ERROR (Status);
> 
> -  //
> -  // Register FtwNotificationEvent () notify function.
> -  //
> -  EfiCreateProtocolNotifyEvent (
> -    &gEfiFaultTolerantWriteProtocolGuid,
> -    TPL_CALLBACK,
> -    FtwNotificationEvent,
> -    (VOID *)SystemTable,
> -    &mFtwRegistration
> -    );
> +  if (!PcdGetBool (PcdEmuVariableNvModeEnable)) {
> +    //
> +    // Register FtwNotificationEvent () notify function.
> +    //
> +    EfiCreateProtocolNotifyEvent (
> +      &gEfiFaultTolerantWriteProtocolGuid,
> +      TPL_CALLBACK,
> +      FtwNotificationEvent,
> +      (VOID *)SystemTable,
> +      &mFtwRegistration
> +      );
> +  } else {
> +    //
> +    // Emulated non-volatile variable mode does not depend on FVB and FTW.
> +    //
> +    VariableWriteServiceInitializeDxe ();
> +  }
> 
>    Status = gBS->CreateEventEx (
>                    EVT_NOTIFY_SIGNAL,
> diff --git
> a/MdeModulePkg/Universal/Variable/RuntimeDxe/VariableRuntimeDxe.inf
> b/MdeModulePkg/Universal/Variable/RuntimeDxe/VariableRuntimeDxe.inf
> index 7ef8a97f5d6a..273067753c25 100644
> --- a/MdeModulePkg/Universal/Variable/RuntimeDxe/VariableRuntimeDxe.inf
> +++ b/MdeModulePkg/Universal/Variable/RuntimeDxe/VariableRuntimeDxe.inf
> @@ -9,7 +9,7 @@
>  #  This external input must be validated carefully to avoid security issues such as
>  #  buffer overflow or integer overflow.
>  #
> -# Copyright (c) 2006 - 2017, Intel Corporation. All rights reserved.<BR>
> +# Copyright (c) 2006 - 2019, Intel Corporation. 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
> @@ -131,6 +131,8 @@ [Pcd]
>    gEfiMdeModulePkgTokenSpaceGuid.PcdMaxUserNvVariableSpaceSize           ##
> CONSUMES
> 
> gEfiMdeModulePkgTokenSpaceGuid.PcdBoottimeReservedNvVariableSpaceSize
> ## CONSUMES
>    gEfiMdeModulePkgTokenSpaceGuid.PcdReclaimVariableSpaceAtEndOfDxe  ##
> CONSUMES
> +  gEfiMdeModulePkgTokenSpaceGuid.PcdEmuVariableNvModeEnable         ##
> SOMETIMES_CONSUMES
> +  gEfiMdeModulePkgTokenSpaceGuid.PcdEmuVariableNvStoreReserved      ##
> SOMETIMES_CONSUMES
> 
>  [FeaturePcd]
>    gEfiMdeModulePkgTokenSpaceGuid.PcdVariableCollectStatistics  ##
> CONSUMES # statistic the information of variable.
> diff --git a/MdeModulePkg/Universal/Variable/RuntimeDxe/VariableSmm.c
> b/MdeModulePkg/Universal/Variable/RuntimeDxe/VariableSmm.c
> index e63af812534e..d47493c891e5 100644
> --- a/MdeModulePkg/Universal/Variable/RuntimeDxe/VariableSmm.c
> +++ b/MdeModulePkg/Universal/Variable/RuntimeDxe/VariableSmm.c
> @@ -1034,17 +1034,24 @@ VariableServiceInitialize (
>                      );
>    ASSERT_EFI_ERROR (Status);
> 
> -  //
> -  // Register FtwNotificationEvent () notify function.
> -  //
> -  Status = gSmst->SmmRegisterProtocolNotify (
> -                    &gEfiSmmFaultTolerantWriteProtocolGuid,
> -                    SmmFtwNotificationEvent,
> -                    &SmmFtwRegistration
> -                    );
> -  ASSERT_EFI_ERROR (Status);
> -
> -  SmmFtwNotificationEvent (NULL, NULL, NULL);
> +  if (!PcdGetBool (PcdEmuVariableNvModeEnable)) {
> +    //
> +    // Register FtwNotificationEvent () notify function.
> +    //
> +    Status = gSmst->SmmRegisterProtocolNotify (
> +                      &gEfiSmmFaultTolerantWriteProtocolGuid,
> +                      SmmFtwNotificationEvent,
> +                      &SmmFtwRegistration
> +                      );
> +    ASSERT_EFI_ERROR (Status);
> +
> +    SmmFtwNotificationEvent (NULL, NULL, NULL);
> +  } else {
> +    //
> +    // Emulated non-volatile variable mode does not depend on FVB and FTW.
> +    //
> +    VariableWriteServiceInitializeSmm ();
> +  }
> 
>    return EFI_SUCCESS;
>  }
> diff --git a/MdeModulePkg/Universal/Variable/RuntimeDxe/VariableSmm.inf
> b/MdeModulePkg/Universal/Variable/RuntimeDxe/VariableSmm.inf
> index db7d220e06df..30d446d06e0d 100644
> --- a/MdeModulePkg/Universal/Variable/RuntimeDxe/VariableSmm.inf
> +++ b/MdeModulePkg/Universal/Variable/RuntimeDxe/VariableSmm.inf
> @@ -18,7 +18,7 @@
>  #  may not be modified without authorization. If platform fails to protect these
> resources,
>  #  the authentication service provided in this driver will be broken, and the
> behavior is undefined.
>  #
> -# Copyright (c) 2010 - 2016, Intel Corporation. All rights reserved.<BR>
> +# Copyright (c) 2010 - 2019, Intel Corporation. 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
> @@ -133,6 +133,8 @@ [Pcd]
>    gEfiMdeModulePkgTokenSpaceGuid.PcdMaxUserNvVariableSpaceSize           ##
> CONSUMES
> 
> gEfiMdeModulePkgTokenSpaceGuid.PcdBoottimeReservedNvVariableSpaceSize
> ## CONSUMES
>    gEfiMdeModulePkgTokenSpaceGuid.PcdReclaimVariableSpaceAtEndOfDxe   ##
> CONSUMES
> +  gEfiMdeModulePkgTokenSpaceGuid.PcdEmuVariableNvModeEnable          ##
> SOMETIMES_CONSUMES
> +  gEfiMdeModulePkgTokenSpaceGuid.PcdEmuVariableNvStoreReserved       ##
> SOMETIMES_CONSUMES
> 
>  [FeaturePcd]
>    gEfiMdeModulePkgTokenSpaceGuid.PcdVariableCollectStatistics        ##
> CONSUMES  # statistic the information of variable.
> --
> 2.7.0.windows.1