[PATCH 0/2] UefiCpuPkg/CpuExceptionHandlerLib: Avoid calling PEI services from AP

[PATCH 0/2] UefiCpuPkg/CpuExceptionHandlerLib: Avoid calling PEI services from AP

[Ruiyu Ni]

1st patch adds more comments to the code to make it more readable.
2nd patch fixes the real assertion issue.

Ruiyu Ni (2):
  CpuExceptionHandlerLib: Add comments to make code more readable
  UefiCpuPkg/CpuExceptionHandlerLib: Avoid calling PEI services from AP

 .../CpuExceptionHandlerLib/CpuExceptionCommon.h    |  7 +-
 .../Ia32/ArchExceptionHandler.c                    |  8 ++-
 .../CpuExceptionHandlerLib/PeiCpuException.c       | 77 +++++++++++++++-------
 .../CpuExceptionHandlerLib/PeiDxeSmmCpuException.c | 12 ++--
 .../X64/ArchExceptionHandler.c                     |  8 ++-
 5 files changed, 73 insertions(+), 39 deletions(-)

-- 
2.16.1.windows.1

[PATCH 1/2] CpuExceptionHandlerLib: Add comments to make code more readable

[Ruiyu Ni]

Today's implementation of handling HOOK_BEFORE and HOOK_AFTER is
a bit complex. More comments is better.

Contributed-under: TianoCore Contribution Agreement 1.1
Signed-off-by: Ruiyu Ni <ruiyu.ni@intel.com>
Cc: Fan Jeff <vanjeff_919@hotmail.com>
Cc: Jian J Wang <jian.j.wang@intel.com>
---
 .../CpuExceptionHandlerLib/Ia32/ArchExceptionHandler.c       |  8 +++++---
 .../Library/CpuExceptionHandlerLib/PeiDxeSmmCpuException.c   | 12 ++++++++----
 .../CpuExceptionHandlerLib/X64/ArchExceptionHandler.c        |  8 +++++---
 3 files changed, 18 insertions(+), 10 deletions(-)

diff --git a/UefiCpuPkg/Library/CpuExceptionHandlerLib/Ia32/ArchExceptionHandler.c b/UefiCpuPkg/Library/CpuExceptionHandlerLib/Ia32/ArchExceptionHandler.c
index 04f2ab593c..031d0d35fa 100644
--- a/UefiCpuPkg/Library/CpuExceptionHandlerLib/Ia32/ArchExceptionHandler.c
+++ b/UefiCpuPkg/Library/CpuExceptionHandlerLib/Ia32/ArchExceptionHandler.c
@@ -1,7 +1,7 @@
 /** @file
   IA32 CPU Exception Handler functons.
 
-  Copyright (c) 2012 - 2017, Intel Corporation. All rights reserved.<BR>
+  Copyright (c) 2012 - 2018, 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
@@ -66,7 +66,9 @@ ArchSaveExceptionContext (
 
   ReservedVectors = ExceptionHandlerData->ReservedVectors;
   //
-  // Save Exception context in global variable
+  // Save Exception context in global variable in first entry of the exception handler.
+  // So when original exception handler returns to the new exception handler (second entry),
+  // the Eflags/Cs/Eip/ExceptionData can be used.
   //
   ReservedVectors[ExceptionType].OldFlags      = SystemContext.SystemContextIa32->Eflags;
   ReservedVectors[ExceptionType].OldCs         = SystemContext.SystemContextIa32->Cs;
@@ -79,7 +81,7 @@ ArchSaveExceptionContext (
   Eflags.Bits.IF = 0;
   SystemContext.SystemContextIa32->Eflags = Eflags.UintN;
   //
-  // Modify the EIP in stack, then old IDT handler will return to the stub code
+  // Modify the EIP in stack, then old IDT handler will return to HookAfterStubBegin.
   //
   SystemContext.SystemContextIa32->Eip    = (UINTN) ReservedVectors[ExceptionType].HookAfterStubHeaderCode;
 }
diff --git a/UefiCpuPkg/Library/CpuExceptionHandlerLib/PeiDxeSmmCpuException.c b/UefiCpuPkg/Library/CpuExceptionHandlerLib/PeiDxeSmmCpuException.c
index 1a382e88fb..64db593194 100644
--- a/UefiCpuPkg/Library/CpuExceptionHandlerLib/PeiDxeSmmCpuException.c
+++ b/UefiCpuPkg/Library/CpuExceptionHandlerLib/PeiDxeSmmCpuException.c
@@ -40,7 +40,8 @@ CommonExceptionHandlerWorker (
   switch (ReservedVectors[ExceptionType].Attribute) {
   case EFI_VECTOR_HANDOFF_HOOK_BEFORE:
     //
-    // Need to jmp to old IDT handler after this exception handler
+    // The new exception handler registered by RegisterCpuInterruptHandler() is executed BEFORE original handler.
+    // Save the original handler to stack so the assembly code can jump to it instead of returning from handler.
     //
     ExceptionHandlerContext->ExceptionDataFlag = (mErrorCodeFlag & (1 << ExceptionType)) ? TRUE : FALSE;
     ExceptionHandlerContext->OldIdtHandler     = ReservedVectors[ExceptionType].ExceptonHandler;
@@ -48,11 +49,13 @@ CommonExceptionHandlerWorker (
   case EFI_VECTOR_HANDOFF_HOOK_AFTER:
     while (TRUE) {
       //
-      // If if anyone has gotten SPIN_LOCK for owner running hook after
+      // If spin-lock can be acquired, it's the first time entering here.
       //
       if (AcquireSpinLockOrFail (&ReservedVectors[ExceptionType].SpinLock)) {
         //
-        // Need to execute old IDT handler before running this exception handler
+        // The new exception handler registered by RegisterCpuInterruptHandler() is executed AFTER original handler.
+        // Save the original handler to stack but skip running the new handler so the original handler is executed
+        // firstly.
         //
         ReservedVectors[ExceptionType].ApicId = GetApicId ();
         ArchSaveExceptionContext (ExceptionType, SystemContext, ExceptionHandlerData);
@@ -61,7 +64,8 @@ CommonExceptionHandlerWorker (
         return;
       }
       //
-      // If failed to acquire SPIN_LOCK, check if it was locked by processor itself
+      // If spin-lock cannot be acquired, it's the second time entering here.
+      // 'break' instead of 'return' is used so the new exception handler can be executed.
       //
       if (ReservedVectors[ExceptionType].ApicId == GetApicId ()) {
         //
diff --git a/UefiCpuPkg/Library/CpuExceptionHandlerLib/X64/ArchExceptionHandler.c b/UefiCpuPkg/Library/CpuExceptionHandlerLib/X64/ArchExceptionHandler.c
index 56180f4c17..93ecf5ae5a 100644
--- a/UefiCpuPkg/Library/CpuExceptionHandlerLib/X64/ArchExceptionHandler.c
+++ b/UefiCpuPkg/Library/CpuExceptionHandlerLib/X64/ArchExceptionHandler.c
@@ -1,7 +1,7 @@
 /** @file
   x64 CPU Exception Handler.
 
-  Copyright (c) 2012 - 2017, Intel Corporation. All rights reserved.<BR>
+  Copyright (c) 2012 - 2018, 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
@@ -67,7 +67,9 @@ ArchSaveExceptionContext (
 
   ReservedVectors = ExceptionHandlerData->ReservedVectors;
   //
-  // Save Exception context in global variable
+  // Save Exception context in global variable in first entry of the exception handler.
+  // So when original exception handler returns to the new exception handler (second entry),
+  // the Eflags/Cs/Eip/ExceptionData can be used.
   //
   ReservedVectors[ExceptionType].OldSs         = SystemContext.SystemContextX64->Ss;
   ReservedVectors[ExceptionType].OldSp         = SystemContext.SystemContextX64->Rsp;
@@ -82,7 +84,7 @@ ArchSaveExceptionContext (
   Eflags.Bits.IF = 0;
   SystemContext.SystemContextX64->Rflags = Eflags.UintN;
   //
-  // Modify the EIP in stack, then old IDT handler will return to the stub code
+  // Modify the EIP in stack, then old IDT handler will return to HookAfterStubBegin.
   //
   SystemContext.SystemContextX64->Rip = (UINTN) ReservedVectors[ExceptionType].HookAfterStubHeaderCode;
 }
-- 
2.16.1.windows.1

[PATCH 2/2] UefiCpuPkg/CpuExceptionHandlerLib: Avoid calling PEI services from AP

[Ruiyu Ni]

REF: https://bugzilla.tianocore.org/show_bug.cgi?id=1128

When an exception happens in AP, system hangs at
GetPeiServicesTablePointer(), complaining the PeiServices retrieved
from memory before IDT is NULL.

Due to the following commit:
c563077a380437c114aba4c95be65eb963ebc1f3
* UefiCpuPkg/MpInitLib: Avoid calling PEI services from AP
the IDT used by AP no longer preserve PeiServices pointer in the
very beginning.
But the implementation of PeiExceptionHandlerLib still assumes
the PeiServices pointer is there, so the assertion happens.

The patch fixes the exception handler library to not call
PEI services from AP.

The patch duplicates the #0 exception stub header in an allocated
pool but with extra 4-byte/8-byte to store the exception handler
data which was originally stored in HOB.
When AP exception happens, the code gets the exception handler data
from the exception handler for #0.

Contributed-under: TianoCore Contribution Agreement 1.1
Signed-off-by: Ruiyu Ni <ruiyu.ni@intel.com>
Cc: Jian J Wang <jian.j.wang@intel.com>
Cc: Fan Jeff <vanjeff_919@hotmail.com>
---
 .../CpuExceptionHandlerLib/CpuExceptionCommon.h    |  7 +-
 .../CpuExceptionHandlerLib/PeiCpuException.c       | 77 +++++++++++++++-------
 2 files changed, 55 insertions(+), 29 deletions(-)

diff --git a/UefiCpuPkg/Library/CpuExceptionHandlerLib/CpuExceptionCommon.h b/UefiCpuPkg/Library/CpuExceptionHandlerLib/CpuExceptionCommon.h
index e10d9379d5..459f06ac84 100644
--- a/UefiCpuPkg/Library/CpuExceptionHandlerLib/CpuExceptionCommon.h
+++ b/UefiCpuPkg/Library/CpuExceptionHandlerLib/CpuExceptionCommon.h
@@ -1,7 +1,7 @@
 /** @file
   Common header file for CPU Exception Handler Library.
 
-  Copyright (c) 2012 - 2017, Intel Corporation. All rights reserved.<BR>
+  Copyright (c) 2012 - 2018, 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
@@ -43,11 +43,6 @@
 
 #include "ArchInterruptDefs.h"
 
-#define CPU_EXCEPTION_HANDLER_LIB_HOB_GUID \
-  { \
-    0xb21d9148, 0x9211, 0x4d8f, { 0xad, 0xd3, 0x66, 0xb1, 0x89, 0xc9, 0x2c, 0x83 } \
-  }
-
 #define CPU_STACK_SWITCH_EXCEPTION_NUMBER \
   FixedPcdGetSize (PcdCpuStackSwitchExceptionList)
 
diff --git a/UefiCpuPkg/Library/CpuExceptionHandlerLib/PeiCpuException.c b/UefiCpuPkg/Library/CpuExceptionHandlerLib/PeiCpuException.c
index 6f271983f2..5dd8423d2f 100644
--- a/UefiCpuPkg/Library/CpuExceptionHandlerLib/PeiCpuException.c
+++ b/UefiCpuPkg/Library/CpuExceptionHandlerLib/PeiCpuException.c
@@ -1,7 +1,7 @@
 /** @file
   CPU exception handler library implementation for PEIM module.
 
-Copyright (c) 2016 - 2017, Intel Corporation. All rights reserved.<BR>
+Copyright (c) 2016 - 2018, 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 that accompanies this distribution.
 The full text of the license may be found at
@@ -20,10 +20,17 @@ WITHOUT WARRANTIES OR REPRESENTATIONS OF ANY KIND, EITHER EXPRESS OR IMPLIED.
 
 CONST UINTN    mDoFarReturnFlag  = 0;
 
-EFI_GUID mCpuExceptrionHandlerLibHobGuid = CPU_EXCEPTION_HANDLER_LIB_HOB_GUID;
+typedef struct {
+  UINT8                   ExceptionStubHeader[HOOKAFTER_STUB_SIZE];
+  EXCEPTION_HANDLER_DATA  *ExceptionHandlerData;
+} EXCEPTION0_STUB_HEADER;
 
 /**
-  Get exception handler data pointer from GUIDed HOb.
+  Get exception handler data pointer from IDT[0].
+
+  The exception #0 stub header is duplicated in an allocated pool with extra 4-byte/8-byte to store the
+  exception handler data. The new allocated memory layout follows structure EXCEPTION0_STUB_HEADER.
+  The code assumes that all processors uses the same exception handler for #0 exception.
 
   @return  pointer to exception handler data.
 **/
@@ -32,18 +39,50 @@ GetExceptionHandlerData (
   VOID
   )
 {
-  EFI_HOB_GUID_TYPE       *GuidHob;
-  VOID                    *DataInHob;
-  EXCEPTION_HANDLER_DATA  *ExceptionHandlerData;
+  IA32_DESCRIPTOR                  IdtDescriptor;
+  IA32_IDT_GATE_DESCRIPTOR         *IdtTable;
+  EXCEPTION0_STUB_HEADER           *Exception0StubHeader;
+
+  AsmReadIdtr (&IdtDescriptor);
+  IdtTable = (IA32_IDT_GATE_DESCRIPTOR *)IdtDescriptor.Base;
+  
+  Exception0StubHeader = (EXCEPTION0_STUB_HEADER *)ArchGetIdtHandler (&IdtTable[0]);
+  return Exception0StubHeader->ExceptionHandlerData;
+}
 
-  ExceptionHandlerData = NULL;
-  GuidHob = GetFirstGuidHob (&mCpuExceptrionHandlerLibHobGuid);
-  if (GuidHob != NULL) {
-    DataInHob = GET_GUID_HOB_DATA (GuidHob);
-    ExceptionHandlerData = (EXCEPTION_HANDLER_DATA *)(*(UINTN *)DataInHob);
-  }
-  ASSERT (ExceptionHandlerData != NULL);
-  return ExceptionHandlerData;
+/**
+  Set exception handler data pointer to IDT[0].
+
+  The exception #0 stub header is duplicated in an allocated pool with extra 4-byte/8-byte to store the
+  exception handler data. The new allocated memory layout follows structure EXCEPTION0_STUB_HEADER.
+  The code assumes that all processors uses the same exception handler for #0 exception.
+
+  @param  pointer to exception handler data.
+**/
+VOID
+SetExceptionHandlerData (
+  IN EXCEPTION_HANDLER_DATA        *ExceptionHandlerData
+  )
+{
+  EXCEPTION0_STUB_HEADER           *Exception0StubHeader;
+  IA32_DESCRIPTOR                  IdtDescriptor;
+  IA32_IDT_GATE_DESCRIPTOR         *IdtTable;
+  //
+  // Duplicate the exception #0 stub header in pool and cache the ExceptionHandlerData just after the stub header.
+  // So AP can get the ExceptionHandlerData by reading the IDT[0].
+  //
+  AsmReadIdtr (&IdtDescriptor);
+  IdtTable = (IA32_IDT_GATE_DESCRIPTOR *)IdtDescriptor.Base;
+  
+  Exception0StubHeader = AllocatePool (sizeof (*Exception0StubHeader));
+  ASSERT (Exception0StubHeader != NULL);
+  CopyMem (
+    Exception0StubHeader->ExceptionStubHeader,
+    (VOID *)ArchGetIdtHandler (&IdtTable[0]),
+    sizeof (Exception0StubHeader->ExceptionStubHeader)
+    );
+  Exception0StubHeader->ExceptionHandlerData = ExceptionHandlerData;
+  ArchUpdateIdtEntry (&IdtTable[0], (UINTN)Exception0StubHeader->ExceptionStubHeader);
 }
 
 /**
@@ -109,15 +148,7 @@ InitializeCpuExceptionHandlers (
     return Status;
   }
 
-  //
-  // Build location of CPU MP DATA buffer in HOB
-  //
-  BuildGuidDataHob (
-    &mCpuExceptrionHandlerLibHobGuid,
-    (VOID *)&ExceptionHandlerData,
-    sizeof(UINT64)
-    );
-
+  SetExceptionHandlerData (ExceptionHandlerData);
   return EFI_SUCCESS;
 }
 
-- 
2.16.1.windows.1

Re: [PATCH 2/2] UefiCpuPkg/CpuExceptionHandlerLib: Avoid calling PEI services from AP

[Wang, Jian J]

Validated-by: Jian J Wang <jian.j.wang@intel.com>
Reviewed-by: Jian J Wang <jian.j.wang@intel.com>

> -----Original Message-----
> From: Ni, Ruiyu
> Sent: Friday, August 31, 2018 4:36 PM
> To: edk2-devel@lists.01.org
> Cc: Wang, Jian J <jian.j.wang@intel.com>; Fan Jeff <vanjeff_919@hotmail.com>
> Subject: [PATCH 2/2] UefiCpuPkg/CpuExceptionHandlerLib: Avoid calling PEI
> services from AP
> 
> REF: https://bugzilla.tianocore.org/show_bug.cgi?id=1128
> 
> When an exception happens in AP, system hangs at
> GetPeiServicesTablePointer(), complaining the PeiServices retrieved
> from memory before IDT is NULL.
> 
> Due to the following commit:
> c563077a380437c114aba4c95be65eb963ebc1f3
> * UefiCpuPkg/MpInitLib: Avoid calling PEI services from AP
> the IDT used by AP no longer preserve PeiServices pointer in the
> very beginning.
> But the implementation of PeiExceptionHandlerLib still assumes
> the PeiServices pointer is there, so the assertion happens.
> 
> The patch fixes the exception handler library to not call
> PEI services from AP.
> 
> The patch duplicates the #0 exception stub header in an allocated
> pool but with extra 4-byte/8-byte to store the exception handler
> data which was originally stored in HOB.
> When AP exception happens, the code gets the exception handler data
> from the exception handler for #0.
> 
> Contributed-under: TianoCore Contribution Agreement 1.1
> Signed-off-by: Ruiyu Ni <ruiyu.ni@intel.com>
> Cc: Jian J Wang <jian.j.wang@intel.com>
> Cc: Fan Jeff <vanjeff_919@hotmail.com>
> ---
>  .../CpuExceptionHandlerLib/CpuExceptionCommon.h    |  7 +-
>  .../CpuExceptionHandlerLib/PeiCpuException.c       | 77 +++++++++++++++-------
>  2 files changed, 55 insertions(+), 29 deletions(-)
> 
> diff --git
> a/UefiCpuPkg/Library/CpuExceptionHandlerLib/CpuExceptionCommon.h
> b/UefiCpuPkg/Library/CpuExceptionHandlerLib/CpuExceptionCommon.h
> index e10d9379d5..459f06ac84 100644
> --- a/UefiCpuPkg/Library/CpuExceptionHandlerLib/CpuExceptionCommon.h
> +++ b/UefiCpuPkg/Library/CpuExceptionHandlerLib/CpuExceptionCommon.h
> @@ -1,7 +1,7 @@
>  /** @file
>    Common header file for CPU Exception Handler Library.
> 
> -  Copyright (c) 2012 - 2017, Intel Corporation. All rights reserved.<BR>
> +  Copyright (c) 2012 - 2018, 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
> @@ -43,11 +43,6 @@
> 
>  #include "ArchInterruptDefs.h"
> 
> -#define CPU_EXCEPTION_HANDLER_LIB_HOB_GUID \
> -  { \
> -    0xb21d9148, 0x9211, 0x4d8f, { 0xad, 0xd3, 0x66, 0xb1, 0x89, 0xc9, 0x2c,
> 0x83 } \
> -  }
> -
>  #define CPU_STACK_SWITCH_EXCEPTION_NUMBER \
>    FixedPcdGetSize (PcdCpuStackSwitchExceptionList)
> 
> diff --git a/UefiCpuPkg/Library/CpuExceptionHandlerLib/PeiCpuException.c
> b/UefiCpuPkg/Library/CpuExceptionHandlerLib/PeiCpuException.c
> index 6f271983f2..5dd8423d2f 100644
> --- a/UefiCpuPkg/Library/CpuExceptionHandlerLib/PeiCpuException.c
> +++ b/UefiCpuPkg/Library/CpuExceptionHandlerLib/PeiCpuException.c
> @@ -1,7 +1,7 @@
>  /** @file
>    CPU exception handler library implementation for PEIM module.
> 
> -Copyright (c) 2016 - 2017, Intel Corporation. All rights reserved.<BR>
> +Copyright (c) 2016 - 2018, 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 that accompanies this distribution.
>  The full text of the license may be found at
> @@ -20,10 +20,17 @@ WITHOUT WARRANTIES OR REPRESENTATIONS OF ANY
> KIND, EITHER EXPRESS OR IMPLIED.
> 
>  CONST UINTN    mDoFarReturnFlag  = 0;
> 
> -EFI_GUID mCpuExceptrionHandlerLibHobGuid =
> CPU_EXCEPTION_HANDLER_LIB_HOB_GUID;
> +typedef struct {
> +  UINT8                   ExceptionStubHeader[HOOKAFTER_STUB_SIZE];
> +  EXCEPTION_HANDLER_DATA  *ExceptionHandlerData;
> +} EXCEPTION0_STUB_HEADER;
> 
>  /**
> -  Get exception handler data pointer from GUIDed HOb.
> +  Get exception handler data pointer from IDT[0].
> +
> +  The exception #0 stub header is duplicated in an allocated pool with extra 4-
> byte/8-byte to store the
> +  exception handler data. The new allocated memory layout follows structure
> EXCEPTION0_STUB_HEADER.
> +  The code assumes that all processors uses the same exception handler for #0
> exception.
> 
>    @return  pointer to exception handler data.
>  **/
> @@ -32,18 +39,50 @@ GetExceptionHandlerData (
>    VOID
>    )
>  {
> -  EFI_HOB_GUID_TYPE       *GuidHob;
> -  VOID                    *DataInHob;
> -  EXCEPTION_HANDLER_DATA  *ExceptionHandlerData;
> +  IA32_DESCRIPTOR                  IdtDescriptor;
> +  IA32_IDT_GATE_DESCRIPTOR         *IdtTable;
> +  EXCEPTION0_STUB_HEADER           *Exception0StubHeader;
> +
> +  AsmReadIdtr (&IdtDescriptor);
> +  IdtTable = (IA32_IDT_GATE_DESCRIPTOR *)IdtDescriptor.Base;
> +
> +  Exception0StubHeader = (EXCEPTION0_STUB_HEADER *)ArchGetIdtHandler
> (&IdtTable[0]);
> +  return Exception0StubHeader->ExceptionHandlerData;
> +}
> 
> -  ExceptionHandlerData = NULL;
> -  GuidHob = GetFirstGuidHob (&mCpuExceptrionHandlerLibHobGuid);
> -  if (GuidHob != NULL) {
> -    DataInHob = GET_GUID_HOB_DATA (GuidHob);
> -    ExceptionHandlerData = (EXCEPTION_HANDLER_DATA *)(*(UINTN
> *)DataInHob);
> -  }
> -  ASSERT (ExceptionHandlerData != NULL);
> -  return ExceptionHandlerData;
> +/**
> +  Set exception handler data pointer to IDT[0].
> +
> +  The exception #0 stub header is duplicated in an allocated pool with extra 4-
> byte/8-byte to store the
> +  exception handler data. The new allocated memory layout follows structure
> EXCEPTION0_STUB_HEADER.
> +  The code assumes that all processors uses the same exception handler for #0
> exception.
> +
> +  @param  pointer to exception handler data.
> +**/
> +VOID
> +SetExceptionHandlerData (
> +  IN EXCEPTION_HANDLER_DATA        *ExceptionHandlerData
> +  )
> +{
> +  EXCEPTION0_STUB_HEADER           *Exception0StubHeader;
> +  IA32_DESCRIPTOR                  IdtDescriptor;
> +  IA32_IDT_GATE_DESCRIPTOR         *IdtTable;
> +  //
> +  // Duplicate the exception #0 stub header in pool and cache the
> ExceptionHandlerData just after the stub header.
> +  // So AP can get the ExceptionHandlerData by reading the IDT[0].
> +  //
> +  AsmReadIdtr (&IdtDescriptor);
> +  IdtTable = (IA32_IDT_GATE_DESCRIPTOR *)IdtDescriptor.Base;
> +
> +  Exception0StubHeader = AllocatePool (sizeof (*Exception0StubHeader));
> +  ASSERT (Exception0StubHeader != NULL);
> +  CopyMem (
> +    Exception0StubHeader->ExceptionStubHeader,
> +    (VOID *)ArchGetIdtHandler (&IdtTable[0]),
> +    sizeof (Exception0StubHeader->ExceptionStubHeader)
> +    );
> +  Exception0StubHeader->ExceptionHandlerData = ExceptionHandlerData;
> +  ArchUpdateIdtEntry (&IdtTable[0], (UINTN)Exception0StubHeader-
> >ExceptionStubHeader);
>  }
> 
>  /**
> @@ -109,15 +148,7 @@ InitializeCpuExceptionHandlers (
>      return Status;
>    }
> 
> -  //
> -  // Build location of CPU MP DATA buffer in HOB
> -  //
> -  BuildGuidDataHob (
> -    &mCpuExceptrionHandlerLibHobGuid,
> -    (VOID *)&ExceptionHandlerData,
> -    sizeof(UINT64)
> -    );
> -
> +  SetExceptionHandlerData (ExceptionHandlerData);
>    return EFI_SUCCESS;
>  }
> 
> --
> 2.16.1.windows.1