[PATCH v2 2/3] IntelFrameworkModulePkg/LegacyBiosDxe: Use macro to enable/disable page 0

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

> v2:
> a. Remove unnecessary braces enclosing code passed to ACCESS_PAGE0_CODE

    EnableNullDetection()
    DisableNullDetection()

to enable/disable page 0. These two methods will check PCD
PcdNullPointerDetectionPropertyMask to know if the page 0 is disabled or not.
This is due to the fact that old GCD service doesn't provide paging related
attributes of memory block. Since this issue has been fixed, GCD services
can be used to determine the paging status of page 0. This is also make it
possible to just use a new macro

    ACCESS_PAGE0_CODE(
      <code accessing page 0>
    );

to replace above methods to do the same job, which also makes code more
readability.

Cc: Liming Gao <liming.gao@intel.com>
Cc: Michael D Kinney <michael.d.kinney@intel.com>
Cc: Ruiyu Ni <ruiyu.ni@intel.com>
Contributed-under: TianoCore Contribution Agreement 1.1
Signed-off-by: Jian J Wang <jian.j.wang@intel.com>
---
 .../Csm/LegacyBiosDxe/LegacyBda.c                  |  53 ++++----
 .../Csm/LegacyBiosDxe/LegacyBios.c                 | 135 ++-------------------
 .../Csm/LegacyBiosDxe/LegacyBiosDxe.inf            |   1 -
 .../Csm/LegacyBiosDxe/LegacyBiosInterface.h        |  16 ---
 .../Csm/LegacyBiosDxe/LegacyBootSupport.c          |  80 ++++++------
 .../Csm/LegacyBiosDxe/LegacyPci.c                  |  72 ++++++-----
 IntelFrameworkModulePkg/Csm/LegacyBiosDxe/Thunk.c  |  51 ++++----
 7 files changed, 135 insertions(+), 273 deletions(-)

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 ();
-
-  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) {
+  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;
+    }
 
-    EnablePs2Keyboard ();
+    if (PciHandle != mVgaHandle) {
 
-    //
-    // Store current mode settings since PrepareToScanRom may change mode.
-    //
-    VideoMode = *(UINT8 *) ((UINTN) (0x400 + BDA_VIDEO_MODE));
-  }
+      EnablePs2Keyboard ();
 
-  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
   //
-- 
2.15.1.windows.2