[PATCH] UefiCpuPkg/MtrrLib: Don't report OutOfResource when MTRR is enough

[Ruiyu Ni <ruiyu.ni@intel.com>]

The MTRR calculation algorithm contains a bug that when left
subtraction cannot produce better MTRR solution, it forgets
to restore the BaseAddress/Length so that MtrrLibGetMtrrNumber()
returns bigger value of actual required MTRR numbers.
As a result, the MtrrLib reports OutOfResource but actually the
MTRR is enough.

MEMORY_RANGE mC[] = {
  0, 0x100000, CacheUncacheable,
  0x100000, 0x89F00000, CacheWriteBack,
  0x8A000000, 0x75000000, CacheUncacheable,
  0xFF000000, 0x01000000, CacheWriteProtected,
  0x100000000, 0x7F00000000, CacheUncacheable,
  0xFC240000, 0x2000, CacheWriteCombining // <-- trigger the error
};

Contributed-under: TianoCore Contribution Agreement 1.0
Signed-off-by: Ruiyu Ni <ruiyu.ni@intel.com>
Cc: Jeff Fan <jeff.fan@intel.com>
---
 UefiCpuPkg/Library/MtrrLib/MtrrLib.c | 10 +++++++++-
 1 file changed, 9 insertions(+), 1 deletion(-)

diff --git a/UefiCpuPkg/Library/MtrrLib/MtrrLib.c b/UefiCpuPkg/Library/MtrrLib/MtrrLib.c
index 9d1927262a..cf1af29936 100644
--- a/UefiCpuPkg/Library/MtrrLib/MtrrLib.c
+++ b/UefiCpuPkg/Library/MtrrLib/MtrrLib.c
@@ -851,6 +851,8 @@ MtrrLibGetMtrrNumber (
   UINT64  SubtractiveLength;
   UINT64  BaseAlignment;
   UINT32  Index;
+  UINT64  OriginalBaseAddress;
+  UINT64  OriginalLength;
 
   *SubLeft = 0;
   *SubRight = 0;
@@ -861,6 +863,9 @@ MtrrLibGetMtrrNumber (
   // Get the optimal left subtraction solution.
   //
   if (BaseAddress != 0) {
+
+    OriginalBaseAddress    = BaseAddress;
+    OriginalLength         = Length;
     SubtractiveBaseAddress = 0;
     SubtractiveLength      = 0;
     //
@@ -915,7 +920,10 @@ MtrrLibGetMtrrNumber (
     //
     if (*SubLeft != 0) {
       BaseAddress = SubtractiveBaseAddress;
-      Length = SubtractiveLength;
+      Length      = SubtractiveLength;
+    } else {
+      BaseAddress = OriginalBaseAddress;
+      Length      = OriginalLength;
     }
   }
 
-- 
2.12.2.windows.2