From c46bced224b42d5a03bc8b207167829aa4e7bc5b Mon Sep 17 00:00:00 2001
From: Jian J Wang <jian.j.wang@intel.com>
Date: Fri, 29 Sep 2017 11:08:27 +0800
Subject: [PATCH] UefiCpuPkg/CpuDxe: Fix assert issue on IA32 platform

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

Cc: 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>
Reviewed-by: Star Zeng <star.zeng@intel.com>
Reviewed-by: Michael Kinney <michael.d.kinney@intel.com>
---
 UefiCpuPkg/CpuDxe/CpuDxe.c | 50 ++++++++++++++++++++++++++++++--------
 1 file changed, 40 insertions(+), 10 deletions(-)

diff --git a/UefiCpuPkg/CpuDxe/CpuDxe.c b/UefiCpuPkg/CpuDxe/CpuDxe.c
index 4e8fa100e0..8ddebabd02 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 +857,46 @@ RefreshGcdMemoryAttributes (
   if (MemorySpaceMap != NULL) {
     FreePool (MemorySpaceMap);
   }
+}
 
-  //
-  // Update page attributes
-  //
-  RefreshGcdMemoryAttributesFromPaging();
+/**
+ Check if paging is enabled or not.
+**/
+BOOLEAN
+IsPagingAndPageAddressExtensionsEnabled (
+  VOID
+  )
+{
+  IA32_CR0  Cr0;
+  IA32_CR4  Cr4;
+
+  Cr0.UintN = AsmReadCr0 ();
+  Cr4.UintN = AsmReadCr4 ();
+
+  return ((Cr0.Bits.PG != 0) && (Cr4.Bits.PAE != 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 (IsPagingAndPageAddressExtensionsEnabled ()) {
+    RefreshGcdMemoryAttributesFromPaging ();
+  }
 
   mIsFlushingGCD = FALSE;
 }
-- 
2.39.2