UefiCpuPkg/CpuDxe: implement non-stop mode for uefi

Same as SMM profile feature, a special #PF is used to set page attribute
to 'present' and a special #DB handler to reset it back to 'not-present',
right after the instruction causing #PF got executed.

Since the new #PF handler won't enter into dead-loop, the instruction
which caused the #PF will get chance to re-execute with accessible pages.

The exception message will still be printed out on debug console so that
the developer/QA can find that there's potential heap overflow or null
pointer access occurred.

Cc: Eric Dong <eric.dong@intel.com>
Cc: Laszlo Ersek <lersek@redhat.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>
Reviewed-by: Eric Dong <eric.dong@intel.com>
Acked-by: Laszlo Ersek <lersek@redhat.com>

UefiCpuPkg/CpuDxe/CpuDxe.h

@@ -57,6 +57,12 @@
                                        EFI_MEMORY_RO    \
                                        )
 
+#define HEAP_GUARD_NONSTOP_MODE       \
+        ((PcdGet8 (PcdHeapGuardPropertyMask) & (BIT6|BIT1|BIT0)) > BIT6)
+
+#define NULL_DETECTION_NONSTOP_MODE   \
+        ((PcdGet8 (PcdNullPointerDetectionPropertyMask) & (BIT6|BIT0)) > BIT6)
+
 /**
   Flush CPU data cache. If the instruction cache is fully coherent
   with all DMA operations then function can just return EFI_SUCCESS.
@@ -273,7 +279,40 @@ RefreshGcdMemoryAttributesFromPaging (
   VOID
   );
 
+/**
+  Special handler for #DB exception, which will restore the page attributes
+  (not-present). It should work with #PF handler which will set pages to
+  'present'.
+
+  @param ExceptionType  Exception type.
+  @param SystemContext  Pointer to EFI_SYSTEM_CONTEXT.
+
+**/
+VOID
+EFIAPI
+DebugExceptionHandler (
+  IN EFI_EXCEPTION_TYPE   InterruptType,
+  IN EFI_SYSTEM_CONTEXT   SystemContext
+  );
+
+/**
+  Special handler for #PF exception, which will set the pages which caused
+  #PF to be 'present'. The attribute of those pages should be restored in
+  the subsequent #DB handler.
+
+  @param ExceptionType  Exception type.
+  @param SystemContext  Pointer to EFI_SYSTEM_CONTEXT.
+
+**/
+VOID
+EFIAPI
+PageFaultExceptionHandler (
+  IN EFI_EXCEPTION_TYPE   InterruptType,
+  IN EFI_SYSTEM_CONTEXT   SystemContext
+  );
+
 extern BOOLEAN mIsAllocatingPageTable;
+extern UINTN   mNumberOfProcessors;
 
 #endif