diff --git a/IntelFrameworkModulePkg/Csm/LegacyBiosDxe/LegacyBda.c b/IntelFrameworkModulePkg/Csm/LegacyBiosDxe/LegacyBda.c
index c6670febee..a94cba435c 100644
--- a/IntelFrameworkModulePkg/Csm/LegacyBiosDxe/LegacyBda.c
+++ b/IntelFrameworkModulePkg/Csm/LegacyBiosDxe/LegacyBda.c
@@ -34,37 +34,36 @@ LegacyBiosInitBda (
   BDA_STRUC *Bda;
   UINT8     *Ebda;
 
-  DisableNullDetection ();
-
   Bda   = (BDA_STRUC *) ((UINTN) 0x400);
   Ebda  = (UINT8 *) ((UINTN) 0x9fc00);
 
-  ZeroMem (Bda, 0x100);
+  ACCESS_PAGE0_CODE (
+    ZeroMem (Bda, 0x100);
+    //
+    // 640k-1k for EBDA
+    //
+    Bda->MemSize        = 0x27f;
+    Bda->KeyHead        = 0x1e;
+    Bda->KeyTail        = 0x1e;
+    Bda->FloppyData     = 0x00;
+    Bda->FloppyTimeout  = 0xff;
+
+    Bda->KeyStart       = 0x001E;
+    Bda->KeyEnd         = 0x003E;
+    Bda->KeyboardStatus = 0x10;
+    Bda->Ebda           = 0x9fc0;
+
+    //
+    // Move LPT time out here and zero out LPT4 since some SCSI OPROMS
+    // use this as scratch pad (LPT4 is Reserved)
+    //
+    Bda->Lpt1_2Timeout  = 0x1414;
+    Bda->Lpt3_4Timeout  = 0x1400;
+
+  );
+
   ZeroMem (Ebda, 0x400);
-  //
-  // 640k-1k for EBDA
-  //
-  Bda->MemSize        = 0x27f;
-  Bda->KeyHead        = 0x1e;
-  Bda->KeyTail        = 0x1e;
-  Bda->FloppyData     = 0x00;
-  Bda->FloppyTimeout  = 0xff;
-
-  Bda->KeyStart       = 0x001E;
-  Bda->KeyEnd         = 0x003E;
-  Bda->KeyboardStatus = 0x10;
-  Bda->Ebda           = 0x9fc0;
-
-  //
-  // Move LPT time out here and zero out LPT4 since some SCSI OPROMS
-  // use this as scratch pad (LPT4 is Reserved)
-  //
-  Bda->Lpt1_2Timeout  = 0x1414;
-  Bda->Lpt3_4Timeout  = 0x1400;
-
-  *Ebda               = 0x01;
-
-  EnableNullDetection ();
+  *Ebda = 0x01;
 
   return EFI_SUCCESS;
 }
diff --git a/IntelFrameworkModulePkg/Csm/LegacyBiosDxe/LegacyBios.c b/IntelFrameworkModulePkg/Csm/LegacyBiosDxe/LegacyBios.c
index c6461f5547..fca08a8fa2 100644
--- a/IntelFrameworkModulePkg/Csm/LegacyBiosDxe/LegacyBios.c
+++ b/IntelFrameworkModulePkg/Csm/LegacyBiosDxe/LegacyBios.c
@@ -786,115 +786,6 @@ ToggleEndOfDxeStatus (
   return;
 }
 
-//
-// Legacy BIOS needs to access memory between 0-4095, which will cause page
-// fault exception if NULL pointer detection mechanism is enabled. Following
-// functions can be used to disable/enable NULL pointer detection before/after
-// accessing those memory.
-//
-
-/**
-   Enable NULL pointer detection.
-**/
-VOID
-EnableNullDetection (
-  VOID
-  )
-{
-  EFI_STATUS                            Status;
-  EFI_GCD_MEMORY_SPACE_DESCRIPTOR       Desc;
-
-  if (((PcdGet8 (PcdNullPointerDetectionPropertyMask) & BIT0) == 0)
-      ||
-      ((mEndOfDxe)  &&
-       ((PcdGet8 (PcdNullPointerDetectionPropertyMask) & (BIT7|BIT0))
-        == (BIT7|BIT0)))
-     ) {
-    return;
-  }
-
-  //
-  // Check current capabilities and attributes
-  //
-  Status = gDS->GetMemorySpaceDescriptor (0, &Desc);
-  ASSERT_EFI_ERROR (Status);
-
-  //
-  // Try to add EFI_MEMORY_RP support if necessary
-  //
-  if ((Desc.Capabilities & EFI_MEMORY_RP) == 0) {
-    Desc.Capabilities |= EFI_MEMORY_RP;
-    Status = gDS->SetMemorySpaceCapabilities (0, EFI_PAGES_TO_SIZE(1),
-                                              Desc.Capabilities);
-    ASSERT_EFI_ERROR (Status);
-    if (EFI_ERROR (Status)) {
-      return;
-    }
-  }
-
-  //
-  // Don't bother if EFI_MEMORY_RP is already set.
-  //
-  if ((Desc.Attributes & EFI_MEMORY_RP) == 0) {
-    Desc.Attributes |= EFI_MEMORY_RP;
-    Status = gDS->SetMemorySpaceAttributes (0, EFI_PAGES_TO_SIZE(1),
-                                            Desc.Attributes);
-    ASSERT_EFI_ERROR (Status);
-  }
-}
-
-/**
-   Disable NULL pointer detection.
-**/
-VOID
-DisableNullDetection (
-  VOID
-  )
-{
-  EFI_STATUS                            Status;
-  EFI_GCD_MEMORY_SPACE_DESCRIPTOR       Desc;
-
-  if (((PcdGet8 (PcdNullPointerDetectionPropertyMask) & BIT0) == 0)
-      ||
-      ((mEndOfDxe)  &&
-       ((PcdGet8 (PcdNullPointerDetectionPropertyMask) & (BIT7|BIT0))
-        == (BIT7|BIT0)))
-     ) {
-    return;
-  }
-
-  //
-  // Check current capabilities and attributes
-  //
-  Status = gDS->GetMemorySpaceDescriptor (0, &Desc);
-  ASSERT_EFI_ERROR (Status);
-
-  //
-  // Try to add EFI_MEMORY_RP support if necessary
-  //
-  if ((Desc.Capabilities & EFI_MEMORY_RP) == 0) {
-    Desc.Capabilities |= EFI_MEMORY_RP;
-    Status = gDS->SetMemorySpaceCapabilities (0, EFI_PAGES_TO_SIZE(1),
-                                              Desc.Capabilities);
-    ASSERT_EFI_ERROR (Status);
-    if (EFI_ERROR (Status)) {
-      return;
-    }
-  }
-
-  //
-  // Don't bother if EFI_MEMORY_RP is already cleared.
-  //
-  if ((Desc.Attributes & EFI_MEMORY_RP) != 0) {
-    Desc.Attributes &= ~EFI_MEMORY_RP;
-    Status = gDS->SetMemorySpaceAttributes (0, EFI_PAGES_TO_SIZE(1),
-                                            Desc.Attributes);
-    ASSERT_EFI_ERROR (Status);
-  } else {
-    DEBUG ((DEBUG_WARN, "!!! Page 0 is supposed to be disabled !!!\r\n"));
-  }
-}
-
 /**
   Install Driver to produce Legacy BIOS protocol.
 
@@ -1095,10 +986,10 @@ LegacyBiosInstall (
   // Initialize region from 0x0000 to 4k. This initializes interrupt vector
   // range.
   //
-  DisableNullDetection ();
-  gBS->SetMem ((VOID *) ClearPtr, 0x400, INITIAL_VALUE_BELOW_1K);
-  ZeroMem ((VOID *) ((UINTN)ClearPtr + 0x400), 0xC00);
-  EnableNullDetection ();
+  ACCESS_PAGE0_CODE (
+    gBS->SetMem ((VOID *) ClearPtr, 0x400, INITIAL_VALUE_BELOW_1K);
+    ZeroMem ((VOID *) ((UINTN)ClearPtr + 0x400), 0xC00);
+  );
 
   //
   // Allocate pages for OPROM usage
@@ -1237,16 +1128,14 @@ LegacyBiosInstall (
   //
   // Save Unexpected interrupt vector so can restore it just prior to boot
   //
-  DisableNullDetection ();
-
-  BaseVectorMaster = (UINT32 *) (sizeof (UINT32) * PROTECTED_MODE_BASE_VECTOR_MASTER);
-  Private->BiosUnexpectedInt = BaseVectorMaster[0];
-  IntRedirCode = (UINT32) (UINTN) Private->IntThunk->InterruptRedirectionCode;
-  for (Index = 0; Index < 8; Index++) {
-    BaseVectorMaster[Index] = (EFI_SEGMENT (IntRedirCode + Index * 4) << 16) | EFI_OFFSET (IntRedirCode + Index * 4);
-  }
-
-  EnableNullDetection ();
+  ACCESS_PAGE0_CODE (
+    BaseVectorMaster = (UINT32 *) (sizeof (UINT32) * PROTECTED_MODE_BASE_VECTOR_MASTER);
+    Private->BiosUnexpectedInt = BaseVectorMaster[0];
+    IntRedirCode = (UINT32) (UINTN) Private->IntThunk->InterruptRedirectionCode;
+    for (Index = 0; Index < 8; Index++) {
+      BaseVectorMaster[Index] = (EFI_SEGMENT (IntRedirCode + Index * 4) << 16) | EFI_OFFSET (IntRedirCode + Index * 4);
+    }
+  );
 
   //
   // Save EFI value
diff --git a/IntelFrameworkModulePkg/Csm/LegacyBiosDxe/LegacyBiosDxe.inf b/IntelFrameworkModulePkg/Csm/LegacyBiosDxe/LegacyBiosDxe.inf
index 6efc7f36ae..180c18e3fc 100644
--- a/IntelFrameworkModulePkg/Csm/LegacyBiosDxe/LegacyBiosDxe.inf
+++ b/IntelFrameworkModulePkg/Csm/LegacyBiosDxe/LegacyBiosDxe.inf
@@ -148,7 +148,6 @@
   gEfiIntelFrameworkModulePkgTokenSpaceGuid.PcdHighPmmMemorySize            ## CONSUMES
   gEfiIntelFrameworkModulePkgTokenSpaceGuid.PcdOpromReservedMemoryBase      ## CONSUMES
   gEfiIntelFrameworkModulePkgTokenSpaceGuid.PcdOpromReservedMemorySize      ## CONSUMES
-  gEfiMdeModulePkgTokenSpaceGuid.PcdNullPointerDetectionPropertyMask        ## CONSUMES
 
 [Depex]
   gEfiLegacyRegion2ProtocolGuid AND gEfiLegacyInterruptProtocolGuid AND gEfiLegacyBiosPlatformProtocolGuid AND gEfiLegacy8259ProtocolGuid AND gEfiGenericMemTestProtocolGuid AND gEfiCpuArchProtocolGuid AND gEfiTimerArchProtocolGuid AND gEfiVariableWriteArchProtocolGuid
diff --git a/IntelFrameworkModulePkg/Csm/LegacyBiosDxe/LegacyBiosInterface.h b/IntelFrameworkModulePkg/Csm/LegacyBiosDxe/LegacyBiosInterface.h
index 86a3b09080..cc2fc9fc13 100644
--- a/IntelFrameworkModulePkg/Csm/LegacyBiosDxe/LegacyBiosInterface.h
+++ b/IntelFrameworkModulePkg/Csm/LegacyBiosDxe/LegacyBiosInterface.h
@@ -1544,20 +1544,4 @@ LegacyBiosInstallVgaRom (
   IN  LEGACY_BIOS_INSTANCE            *Private
   );
 
-/**
-   Enable NULL pointer detection.
-**/
-VOID
-EnableNullDetection (
-  VOID
-  );
-
-/**
-   Disable NULL pointer detection.
-**/
-VOID
-DisableNullDetection (
-  VOID
-  );
-
 #endif
diff --git a/IntelFrameworkModulePkg/Csm/LegacyBiosDxe/LegacyBootSupport.c b/IntelFrameworkModulePkg/Csm/LegacyBiosDxe/LegacyBootSupport.c
index c2ac69ce69..57ab78d648 100644
--- a/IntelFrameworkModulePkg/Csm/LegacyBiosDxe/LegacyBootSupport.c
+++ b/IntelFrameworkModulePkg/Csm/LegacyBiosDxe/LegacyBootSupport.c
@@ -1041,7 +1041,9 @@ GenericLegacyBoot (
   //
   // Setup BDA and EBDA standard areas before Legacy Boot
   //
-  LegacyBiosCompleteBdaBeforeBoot (Private);
+  ACCESS_PAGE0_CODE (
+    LegacyBiosCompleteBdaBeforeBoot (Private);
+  );
   LegacyBiosCompleteStandardCmosBeforeBoot (Private);
 
   //
@@ -1073,10 +1075,10 @@ GenericLegacyBoot (
   // Use 182/10 to avoid floating point math.
   //
   LocalTime = (LocalTime * 182) / 10;
-  DisableNullDetection ();
-  BdaPtr    = (UINT32 *) (UINTN)0x46C;
-  *BdaPtr   = LocalTime;
-  EnableNullDetection ();
+  ACCESS_PAGE0_CODE (
+    BdaPtr    = (UINT32 *) (UINTN)0x46C;
+    *BdaPtr   = LocalTime;
+  );
 
   //
   // Shadow PCI ROMs. We must do this near the end since this will kick
@@ -1322,15 +1324,15 @@ GenericLegacyBoot (
     //          set of TIANO vectors) or takes it over.
     //
     //
-    DisableNullDetection ();
-    BaseVectorMaster = (UINT32 *) (sizeof (UINT32) * PROTECTED_MODE_BASE_VECTOR_MASTER);
-    for (Index = 0; Index < 8; Index++) {
-      Private->ThunkSavedInt[Index] = BaseVectorMaster[Index];
-      if (Private->ThunkSeg == (UINT16) (BaseVectorMaster[Index] >> 16)) {
-        BaseVectorMaster[Index] = (UINT32) (Private->BiosUnexpectedInt);
+    ACCESS_PAGE0_CODE (
+      BaseVectorMaster = (UINT32 *) (sizeof (UINT32) * PROTECTED_MODE_BASE_VECTOR_MASTER);
+      for (Index = 0; Index < 8; Index++) {
+        Private->ThunkSavedInt[Index] = BaseVectorMaster[Index];
+        if (Private->ThunkSeg == (UINT16) (BaseVectorMaster[Index] >> 16)) {
+          BaseVectorMaster[Index] = (UINT32) (Private->BiosUnexpectedInt);
+        }
       }
-    }
-    EnableNullDetection ();
+    );
 
     ZeroMem (&Regs, sizeof (EFI_IA32_REGISTER_SET));
     Regs.X.AX = Legacy16Boot;
@@ -1344,12 +1346,12 @@ GenericLegacyBoot (
       0
       );
 
-    DisableNullDetection ();
-    BaseVectorMaster = (UINT32 *) (sizeof (UINT32) * PROTECTED_MODE_BASE_VECTOR_MASTER);
-    for (Index = 0; Index < 8; Index++) {
-      BaseVectorMaster[Index] = Private->ThunkSavedInt[Index];
-    }
-    EnableNullDetection ();
+    ACCESS_PAGE0_CODE (
+      BaseVectorMaster = (UINT32 *) (sizeof (UINT32) * PROTECTED_MODE_BASE_VECTOR_MASTER);
+      for (Index = 0; Index < 8; Index++) {
+        BaseVectorMaster[Index] = Private->ThunkSavedInt[Index];
+      }
+    );
   }
   Private->LegacyBootEntered = TRUE;
   if ((mBootMode == BOOT_LEGACY_OS) || (mBootMode == BOOT_UNCONVENTIONAL_DEVICE)) {
@@ -1737,11 +1739,11 @@ LegacyBiosBuildE820 (
   //
   // First entry is 0 to (640k - EBDA)
   //
-  DisableNullDetection ();
-  E820Table[0].BaseAddr  = 0;
-  E820Table[0].Length    = (UINT64) ((*(UINT16 *) (UINTN)0x40E) << 4);
-  E820Table[0].Type      = EfiAcpiAddressRangeMemory;
-  EnableNullDetection ();
+  ACCESS_PAGE0_CODE (
+    E820Table[0].BaseAddr  = 0;
+    E820Table[0].Length    = (UINT64) ((*(UINT16 *) (UINTN)0x40E) << 4);
+    E820Table[0].Type      = EfiAcpiAddressRangeMemory;
+  );
 
   //
   // Second entry is (640k - EBDA) to 640k
@@ -1975,8 +1977,6 @@ LegacyBiosCompleteBdaBeforeBoot (
   UINT16                      MachineConfig;
   DEVICE_PRODUCER_DATA_HEADER *SioPtr;
 
-  DisableNullDetection ();
-
   Bda           = (BDA_STRUC *) ((UINTN) 0x400);
   MachineConfig = 0;
 
@@ -2035,8 +2035,6 @@ LegacyBiosCompleteBdaBeforeBoot (
   MachineConfig       = (UINT16) (MachineConfig + 0x00 + 0x02 + (SioPtr->MousePresent * 0x04));
   Bda->MachineConfig  = MachineConfig;
 
-  EnableNullDetection ();
-
   return EFI_SUCCESS;
 }
 
@@ -2063,17 +2061,15 @@ LegacyBiosUpdateKeyboardLedStatus (
 
   Private             = LEGACY_BIOS_INSTANCE_FROM_THIS (This);
 
-  DisableNullDetection ();
-
-  Bda                 = (BDA_STRUC *) ((UINTN) 0x400);
-  LocalLeds           = Leds;
-  Bda->LedStatus      = (UINT8) ((Bda->LedStatus &~0x07) | LocalLeds);
-  LocalLeds           = (UINT8) (LocalLeds << 4);
-  Bda->ShiftStatus    = (UINT8) ((Bda->ShiftStatus &~0x70) | LocalLeds);
-  LocalLeds           = (UINT8) (Leds & 0x20);
-  Bda->KeyboardStatus = (UINT8) ((Bda->KeyboardStatus &~0x20) | LocalLeds);
-
-  EnableNullDetection ();
+  ACCESS_PAGE0_CODE (
+    Bda                 = (BDA_STRUC *) ((UINTN) 0x400);
+    LocalLeds           = Leds;
+    Bda->LedStatus      = (UINT8) ((Bda->LedStatus &~0x07) | LocalLeds);
+    LocalLeds           = (UINT8) (LocalLeds << 4);
+    Bda->ShiftStatus    = (UINT8) ((Bda->ShiftStatus &~0x70) | LocalLeds);
+    LocalLeds           = (UINT8) (Leds & 0x20);
+    Bda->KeyboardStatus = (UINT8) ((Bda->KeyboardStatus &~0x20) | LocalLeds);
+  );
 
   //
   // Call into Legacy16 code to allow it to do any processing
@@ -2119,9 +2115,9 @@ LegacyBiosCompleteStandardCmosBeforeBoot (
   //            to large capacity drives
   // CMOS 14 = BDA 40:10 plus bit 3(display enabled)
   //
-  DisableNullDetection ();
-  Bda = (UINT8)(*((UINT8 *)((UINTN)0x410)) | BIT3);
-  EnableNullDetection ();
+  ACCESS_PAGE0_CODE (
+    Bda = (UINT8)(*((UINT8 *)((UINTN)0x410)) | BIT3);
+  );
 
   //
   // Force display enabled
diff --git a/IntelFrameworkModulePkg/Csm/LegacyBiosDxe/LegacyPci.c b/IntelFrameworkModulePkg/Csm/LegacyBiosDxe/LegacyPci.c
index d38cef3e33..b10a9dcef6 100644
--- a/IntelFrameworkModulePkg/Csm/LegacyBiosDxe/LegacyPci.c
+++ b/IntelFrameworkModulePkg/Csm/LegacyBiosDxe/LegacyPci.c
@@ -2403,35 +2403,33 @@ LegacyBiosInstallRom (
   // 2. BBS compliants drives will not change 40:75 until boot time.
   // 3. Onboard IDE controllers will change 40:75
   //
-  DisableNullDetection ();
+  ACCESS_PAGE0_CODE (
+    LocalDiskStart = (UINT8) ((*(UINT8 *) ((UINTN) 0x475)) + 0x80);
+    if ((Private->Disk4075 + 0x80) < LocalDiskStart) {
+      //
+      // Update table since onboard IDE drives found
+      //
+      Private->LegacyEfiHddTable[Private->LegacyEfiHddTableIndex].PciSegment        = 0xff;
+      Private->LegacyEfiHddTable[Private->LegacyEfiHddTableIndex].PciBus            = 0xff;
+      Private->LegacyEfiHddTable[Private->LegacyEfiHddTableIndex].PciDevice         = 0xff;
+      Private->LegacyEfiHddTable[Private->LegacyEfiHddTableIndex].PciFunction       = 0xff;
+      Private->LegacyEfiHddTable[Private->LegacyEfiHddTableIndex].StartDriveNumber  = (UINT8) (Private->Disk4075 + 0x80);
+      Private->LegacyEfiHddTable[Private->LegacyEfiHddTableIndex].EndDriveNumber    = LocalDiskStart;
+      Private->LegacyEfiHddTableIndex ++;
+      Private->Disk4075 = (UINT8) (LocalDiskStart & 0x7f);
+      Private->DiskEnd  = LocalDiskStart;
+    }
 
-  LocalDiskStart = (UINT8) ((*(UINT8 *) ((UINTN) 0x475)) + 0x80);
-  if ((Private->Disk4075 + 0x80) < LocalDiskStart) {
-    //
-    // Update table since onboard IDE drives found
-    //
-    Private->LegacyEfiHddTable[Private->LegacyEfiHddTableIndex].PciSegment        = 0xff;
-    Private->LegacyEfiHddTable[Private->LegacyEfiHddTableIndex].PciBus            = 0xff;
-    Private->LegacyEfiHddTable[Private->LegacyEfiHddTableIndex].PciDevice         = 0xff;
-    Private->LegacyEfiHddTable[Private->LegacyEfiHddTableIndex].PciFunction       = 0xff;
-    Private->LegacyEfiHddTable[Private->LegacyEfiHddTableIndex].StartDriveNumber  = (UINT8) (Private->Disk4075 + 0x80);
-    Private->LegacyEfiHddTable[Private->LegacyEfiHddTableIndex].EndDriveNumber    = LocalDiskStart;
-    Private->LegacyEfiHddTableIndex ++;
-    Private->Disk4075 = (UINT8) (LocalDiskStart & 0x7f);
-    Private->DiskEnd  = LocalDiskStart;
-  }
+    if (PciHandle != mVgaHandle) {
 
-  if (PciHandle != mVgaHandle) {
+      EnablePs2Keyboard ();
 
-    EnablePs2Keyboard ();
-
-    //
-    // Store current mode settings since PrepareToScanRom may change mode.
-    //
-    VideoMode = *(UINT8 *) ((UINTN) (0x400 + BDA_VIDEO_MODE));
-  }
-
-  EnableNullDetection ();
+      //
+      // Store current mode settings since PrepareToScanRom may change mode.
+      //
+      VideoMode = *(UINT8 *) ((UINTN) (0x400 + BDA_VIDEO_MODE));
+    }
+  );
 
   //
   // Notify the platform that we are about to scan the ROM
@@ -2473,11 +2471,11 @@ LegacyBiosInstallRom (
   // Multiply result by 18.2 for number of ticks since midnight.
   // Use 182/10 to avoid floating point math.
   //
-  DisableNullDetection ();
-  LocalTime = (LocalTime * 182) / 10;
-  BdaPtr    = (UINT32 *) ((UINTN) 0x46C);
-  *BdaPtr   = LocalTime;
-  EnableNullDetection ();
+  ACCESS_PAGE0_CODE (
+    LocalTime = (LocalTime * 182) / 10;
+    BdaPtr    = (UINT32 *) ((UINTN) 0x46C);
+    *BdaPtr   = LocalTime;
+  );
   
   //
   // Pass in handoff data
@@ -2573,9 +2571,9 @@ LegacyBiosInstallRom (
     //
     // Set mode settings since PrepareToScanRom may change mode
     //
-    DisableNullDetection ();
-    OldVideoMode = *(UINT8 *) ((UINTN) (0x400 + BDA_VIDEO_MODE));
-    EnableNullDetection ();
+    ACCESS_PAGE0_CODE ({
+      OldVideoMode = *(UINT8 *) ((UINTN) (0x400 + BDA_VIDEO_MODE));
+    });
 
     if (VideoMode != OldVideoMode) {
       //
@@ -2617,9 +2615,9 @@ LegacyBiosInstallRom (
     }
   }
 
-  DisableNullDetection ();
-  LocalDiskEnd = (UINT8) ((*(UINT8 *) ((UINTN) 0x475)) + 0x80);
-  EnableNullDetection ();
+  ACCESS_PAGE0_CODE (
+    LocalDiskEnd = (UINT8) ((*(UINT8 *) ((UINTN) 0x475)) + 0x80);
+  );
   
   //
   // Allow platform to perform any required actions after the
diff --git a/IntelFrameworkModulePkg/Csm/LegacyBiosDxe/Thunk.c b/IntelFrameworkModulePkg/Csm/LegacyBiosDxe/Thunk.c
index d249479c56..d330f4870b 100644
--- a/IntelFrameworkModulePkg/Csm/LegacyBiosDxe/Thunk.c
+++ b/IntelFrameworkModulePkg/Csm/LegacyBiosDxe/Thunk.c
@@ -73,10 +73,10 @@ LegacyBiosInt86 (
   // The base address of legacy interrupt vector table is 0.
   // We use this base address to get the legacy interrupt handler.
   //
-  DisableNullDetection ();
-  Segment               = (UINT16)(((UINT32 *)0)[BiosInt] >> 16);
-  Offset                = (UINT16)((UINT32 *)0)[BiosInt];
-  EnableNullDetection ();
+  ACCESS_PAGE0_CODE (
+    Segment               = (UINT16)(((UINT32 *)0)[BiosInt] >> 16);
+    Offset                = (UINT16)((UINT32 *)0)[BiosInt];
+  );
   
   return InternalLegacyBiosFarCall (
            This,
@@ -286,29 +286,6 @@ InternalLegacyBiosFarCall (
 
   AsmThunk16 (&mThunkContext);
 
-  //
-  // OPROM may allocate EBDA range by itself and change EBDA base and EBDA size.
-  // Get the current EBDA base address, and compared with pre-allocate minimum
-  // EBDA base address, if the current EBDA base address is smaller, it indicates
-  // PcdEbdaReservedMemorySize should be adjusted to larger for more OPROMs.
-  //
-  DEBUG_CODE (
-    {
-      UINTN                 EbdaBaseAddress;
-      UINTN                 ReservedEbdaBaseAddress;
-
-      //
-      // Skip this part of debug code if NULL pointer detection is enabled
-      //
-      if ((PcdGet8 (PcdNullPointerDetectionPropertyMask) & BIT0) == 0) {
-        EbdaBaseAddress = (*(UINT16 *) (UINTN) 0x40E) << 4;
-        ReservedEbdaBaseAddress = CONVENTIONAL_MEMORY_TOP
-                                  - PcdGet32 (PcdEbdaReservedMemorySize);
-        ASSERT (ReservedEbdaBaseAddress <= EbdaBaseAddress);
-      }
-    }
-  );
-
   if (Stack != NULL && StackSize != 0) {
     //
     // Copy low memory stack to Stack
@@ -334,6 +311,26 @@ InternalLegacyBiosFarCall (
   //
   gBS->RestoreTPL (OriginalTpl);
   
+  //
+  // OPROM may allocate EBDA range by itself and change EBDA base and EBDA size.
+  // Get the current EBDA base address, and compared with pre-allocate minimum
+  // EBDA base address, if the current EBDA base address is smaller, it indicates
+  // PcdEbdaReservedMemorySize should be adjusted to larger for more OPROMs.
+  //
+  DEBUG_CODE (
+    {
+      UINTN                 EbdaBaseAddress;
+      UINTN                 ReservedEbdaBaseAddress;
+
+      ACCESS_PAGE0_CODE (
+        EbdaBaseAddress = (*(UINT16 *) (UINTN) 0x40E) << 4;
+        ReservedEbdaBaseAddress = CONVENTIONAL_MEMORY_TOP
+                                  - PcdGet32 (PcdEbdaReservedMemorySize);
+        ASSERT (ReservedEbdaBaseAddress <= EbdaBaseAddress);
+      );
+    }
+  );
+
   //
   // Restore interrupt of debug timer
   //