[Patch V2 04/14] UefiCpuPkg/CpuPageTableLib: Fix issue when splitting leaf entry

["duntan" <dun.tan@intel.com>]

When splitting leaf parent entry to smaller granularity, create
child page table before modifing parent entry. In previous code
logic, when splitting a leaf parent entry, parent entry will
point to a null 4k memory before child page table is created in
this 4k memory. When the page table to be modified is the page
table in CR3, if the executed CpuPageTableLib code is in the
range mapped by the modified leaf parent entry, then issue will
happen.

Signed-off-by: Dun Tan <dun.tan@intel.com>
Cc: Eric Dong <eric.dong@intel.com>
Cc: Ray Ni <ray.ni@intel.com>
Cc: Rahul Kumar <rahul1.kumar@intel.com>
Cc: Gerd Hoffmann <kraxel@redhat.com>
---
 UefiCpuPkg/Library/CpuPageTableLib/CpuPageTableMap.c | 17 +++++++++--------
 1 file changed, 9 insertions(+), 8 deletions(-)

diff --git a/UefiCpuPkg/Library/CpuPageTableLib/CpuPageTableMap.c b/UefiCpuPkg/Library/CpuPageTableLib/CpuPageTableMap.c
index ee27238edb..0f3d0d684e 100644
--- a/UefiCpuPkg/Library/CpuPageTableLib/CpuPageTableMap.c
+++ b/UefiCpuPkg/Library/CpuPageTableLib/CpuPageTableMap.c
@@ -354,8 +354,15 @@ PageTableLibMapInLevel (
       //
       // Create 512 child-level entries that map to 2M/4K.
       //
-      ParentPagingEntry->Uintn = (UINTN)Buffer + *BufferSize;
-      ZeroMem ((VOID *)ParentPagingEntry->Uintn, SIZE_4KB);
+      PagingEntry = (IA32_PAGING_ENTRY *)((UINTN)Buffer + *BufferSize);
+      ZeroMem (PagingEntry, SIZE_4KB);
+
+      for (SubOffset = 0, Index = 0; Index < 512; Index++) {
+        PagingEntry[Index].Uint64 = OneOfPagingEntry.Uint64 + SubOffset;
+        SubOffset                += RegionLength;
+      }
+
+      ParentPagingEntry->Uintn = (UINTN)(VOID *)PagingEntry;
 
       //
       // Set NOP attributes
@@ -363,12 +370,6 @@ PageTableLibMapInLevel (
       //       will make the entire region read-only even the child entries set the RW bit.
       //
       PageTableLibSetPnle (&ParentPagingEntry->Pnle, &NopAttribute, &AllOneMask);
-
-      PagingEntry = (IA32_PAGING_ENTRY *)(UINTN)IA32_PNLE_PAGE_TABLE_BASE_ADDRESS (&ParentPagingEntry->Pnle);
-      for (SubOffset = 0, Index = 0; Index < 512; Index++) {
-        PagingEntry[Index].Uint64 = OneOfPagingEntry.Uint64 + SubOffset;
-        SubOffset                += RegionLength;
-      }
     }
   } else {
     //
-- 
2.31.1.windows.1