[PATCH] UefiCpuPkg/CpuDxe: Fix assert issue on IA32 platform

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

This patch is to fix an assert issue during booting IA32 platforms
such as OvmfIa32 or Quark. This issue is caused by trying to access
page table on a platform without page table. A check is added to
avoid the assert.

Bug tracker: https://bugzilla.tianocore.org/show_bug.cgi?id=724

c: Star Zeng <star.zeng@intel.com>
Cc: Jiewen Yao <jiewen.yao@intel.com>
Cc: Michael Kinney <michael.d.kinney@intel.com>
Contributed-under: TianoCore Contribution Agreement 1.1
Signed-off-by: Jian J Wang <jian.j.wang@intel.com>
---
 UefiCpuPkg/CpuDxe/CpuDxe.c | 48 ++++++++++++++++++++++++++++++++++++----------
 1 file changed, 38 insertions(+), 10 deletions(-)

diff --git a/UefiCpuPkg/CpuDxe/CpuDxe.c b/UefiCpuPkg/CpuDxe/CpuDxe.c
index 4e8fa100e0..85a520079f 100644
--- a/UefiCpuPkg/CpuDxe/CpuDxe.c
+++ b/UefiCpuPkg/CpuDxe/CpuDxe.c
@@ -683,7 +683,7 @@ SetGcdMemorySpaceAttributes (
 
 **/
 VOID
-RefreshGcdMemoryAttributes (
+RefreshMemoryAttributesFromMtrr (
   VOID
   )
 {
@@ -704,14 +704,9 @@ RefreshGcdMemoryAttributes (
   UINT32                              FirmwareVariableMtrrCount;
   UINT8                               DefaultMemoryType;
 
-  if (!IsMtrrSupported ()) {
-    return;
-  }
-
   FirmwareVariableMtrrCount = GetFirmwareVariableMtrrCount ();
   ASSERT (FirmwareVariableMtrrCount <= MTRR_NUMBER_OF_VARIABLE_MTRR);
 
-  mIsFlushingGCD = TRUE;
   MemorySpaceMap = NULL;
 
   //
@@ -862,11 +857,44 @@ RefreshGcdMemoryAttributes (
   if (MemorySpaceMap != NULL) {
     FreePool (MemorySpaceMap);
   }
+}
 
-  //
-  // Update page attributes
-  //
-  RefreshGcdMemoryAttributesFromPaging();
+/**
+ Check if paging is enabled or not.
+**/
+BOOLEAN
+IsPagingSupported (
+  VOID
+  )
+{
+  return (
+          (AsmReadCr0 () & BIT31) != 0
+          &&
+          (AsmReadCr4 () & BIT5) != 0
+         );
+}
+
+/**
+  Refreshes the GCD Memory Space attributes according to MTRRs and Paging.
+
+  This function refreshes the GCD Memory Space attributes according to MTRRs
+  and page tables.
+
+**/
+VOID
+RefreshGcdMemoryAttributes (
+  VOID
+  )
+{
+  mIsFlushingGCD = TRUE;
+
+  if (IsMtrrSupported ()) {
+    RefreshMemoryAttributesFromMtrr ();
+  }
+
+  if (IsPagingSupported ()) {
+    RefreshGcdMemoryAttributesFromPaging ();
+  }
 
   mIsFlushingGCD = FALSE;
 }
-- 
2.14.1.windows.1