Needn't to copy register table if AllocatedSize is 0.

v4:
  Fix potential uninitialized variable issue.

Cc: Feng Tian <feng.tian@intel.com>
Cc: Michael Kinney <michael.d.kinney@intel.com>
Contributed-under: TianoCore Contribution Agreement 1.0
Signed-off-by: Jeff Fan <jeff.fan@intel.com>
---
 UefiCpuPkg/PiSmmCpuDxeSmm/CpuS3.c | 27 +++++++++++++++------------
 1 file changed, 15 insertions(+), 12 deletions(-)

diff --git a/UefiCpuPkg/PiSmmCpuDxeSmm/CpuS3.c b/UefiCpuPkg/PiSmmCpuDxeSmm/CpuS3.c
index 12efc1f..2588979 100644
--- a/UefiCpuPkg/PiSmmCpuDxeSmm/CpuS3.c
+++ b/UefiCpuPkg/PiSmmCpuDxeSmm/CpuS3.c
@@ -826,18 +826,21 @@ CopyRegisterTable (
 
   CopyMem (DestinationRegisterTableList, SourceRegisterTableList, NumberOfCpus * sizeof (CPU_REGISTER_TABLE));
   for (Index = 0; Index < NumberOfCpus; Index++) {
-    RegisterTableEntry = AllocatePool (DestinationRegisterTableList[Index].AllocatedSize);
-    ASSERT (RegisterTableEntry != NULL);
-    CopyMem (RegisterTableEntry, (VOID *)(UINTN)SourceRegisterTableList[Index].RegisterTableEntry, DestinationRegisterTableList[Index].AllocatedSize);
-    //
-    // Go though all MSRs in register table to initialize MSR spin lock
-    //
-    for (Index1 = 0; Index1 < DestinationRegisterTableList[Index].TableLength; Index1++, RegisterTableEntry++) {
-      if ((RegisterTableEntry->RegisterType == Msr) && (RegisterTableEntry->ValidBitLength < 64)) {
-        //
-        // Initialize MSR spin lock only for those MSRs need bit field writing
-        //
-        InitMsrSpinLockByIndex (RegisterTableEntry->Index);
+    RegisterTableEntry = NULL;
+    if (DestinationRegisterTableList[Index].AllocatedSize != 0) {
+      RegisterTableEntry = AllocatePool (DestinationRegisterTableList[Index].AllocatedSize);
+      ASSERT (RegisterTableEntry != NULL);
+      CopyMem (RegisterTableEntry, (VOID *)(UINTN)SourceRegisterTableList[Index].RegisterTableEntry, DestinationRegisterTableList[Index].AllocatedSize);
+      //
+      // Go though all MSRs in register table to initialize MSR spin lock
+      //
+      for (Index1 = 0; Index1 < DestinationRegisterTableList[Index].TableLength; Index1++, RegisterTableEntry++) {
+        if ((RegisterTableEntry->RegisterType == Msr) && (RegisterTableEntry->ValidBitLength < 64)) {
+          //
+          // Initialize MSR spin lock only for those MSRs need bit field writing
+          //
+          InitMsrSpinLockByIndex (RegisterTableEntry->Index);
+        }
       }
     }
     DestinationRegisterTableList[Index].RegisterTableEntry = (EFI_PHYSICAL_ADDRESS)(UINTN)RegisterTableEntry;
-- 
2.9.3.windows.2

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