[PATCH 09/10] CpuPageTableLib: Fix bug that wrongly requires extra size for mapping

["Ni, Ray" <ray.ni@intel.com>]

With following paging structure to map
  [2M-4K, 2M] as P = 1, RW = 0,
  [2M, 4M]    as P = 1, RW = 1:

PML4[0] -> PDPTE[0] -> PDE[0](RW = 0) -> PTE[255](P = 0, RW = 0)
                    -> PDE[1](RW = 1)

When a new request to map [2M-4K, 2M+4K] as P = 1, RW = 1,
CpuPageTableMap() wrongly requests 4K buffer size for the new mapping
request.

But in fact, for [2M-4K, 2M] request, PTE[255] can be changed in place,
for [2M, 2M+4K], no change is needed because PDE[1].RW = 1 already.

The change fixes the bug.

Signed-off-by: Ray Ni <ray.ni@intel.com>
Signed-off-by: Zhiguang Liu <zhiguang.liu@intel.com>
Cc: Eric Dong <eric.dong@intel.com>
---
 .../Library/CpuPageTableLib/CpuPageTableMap.c       | 13 +++++--------
 1 file changed, 5 insertions(+), 8 deletions(-)

diff --git a/UefiCpuPkg/Library/CpuPageTableLib/CpuPageTableMap.c b/UefiCpuPkg/Library/CpuPageTableLib/CpuPageTableMap.c
index 1205119fc8..16e6697ed4 100644
--- a/UefiCpuPkg/Library/CpuPageTableLib/CpuPageTableMap.c
+++ b/UefiCpuPkg/Library/CpuPageTableLib/CpuPageTableMap.c
@@ -272,6 +272,7 @@ PageTableLibMapInLevel (
   IA32_MAP_ATTRIBUTE  ChildAttribute;
   IA32_MAP_ATTRIBUTE  ChildMask;
   IA32_MAP_ATTRIBUTE  CurrentMask;
+  IA32_MAP_ATTRIBUTE  LocalParentAttribute;
 
   ASSERT (Level != 0);
   ASSERT ((Attribute != NULL) && (Mask != NULL));
@@ -284,6 +285,9 @@ PageTableLibMapInLevel (
   NopAttribute.Bits.ReadWrite      = 1;
   NopAttribute.Bits.UserSupervisor = 1;
 
+  LocalParentAttribute.Uint64 = ParentAttribute->Uint64;
+  ParentAttribute             = &LocalParentAttribute;
+
   //
   // ParentPagingEntry ONLY is deferenced for checking Present and MustBeOne bits
   // when Modify is FALSE.
@@ -420,7 +424,7 @@ PageTableLibMapInLevel (
           }
 
           if (IsPle (&PagingEntry[Index], Level)) {
-            PageTableLibSetPle (Level - 1, &PagingEntry[Index], 0, &ChildAttribute, &ChildMask);
+            PageTableLibSetPle (Level, &PagingEntry[Index], 0, &ChildAttribute, &ChildMask);
           } else {
             PageTableLibSetPnle (&PagingEntry[Index].Pnle, &ChildAttribute, &ChildMask);
           }
@@ -664,13 +668,6 @@ PageTableMap (
   //
   // Update the page table when the supplied buffer is sufficient.
   //
-  ParentAttribute.Uint64                    = 0;
-  ParentAttribute.Bits.PageTableBaseAddress = 1;
-  ParentAttribute.Bits.Present              = 1;
-  ParentAttribute.Bits.ReadWrite            = 1;
-  ParentAttribute.Bits.UserSupervisor       = 1;
-  ParentAttribute.Bits.Nx                   = 0;
-
   Status = PageTableLibMapInLevel (
              &TopPagingEntry,
              &ParentAttribute,
-- 
2.35.1.windows.2