[PATCH] UefiCpuPkg RegisterCpuFeaturesLib: Fix an ASSERTION issue

["Zeng, Star" <star.zeng@intel.com>]

BZ: https://bugzilla.tianocore.org/show_bug.cgi?id=1968

We met assertion like below, it happens when there is only
one processor.

ASSERT_EFI_ERROR (Status = Not started)
ASSERT [CpuFeaturesDxe] X:\XXX\XXX\RegisterCpuFeaturesLib\
  DxeRegisterCpuFeaturesLib.c(149): !EFI_ERROR (Status)

The code should not call StartupAllAPs when there is only one processor.

Cc: Laszlo Ersek <lersek@redhat.com>
Cc: Eric Dong <eric.dong@intel.com>
Cc: Ray Ni <ray.ni@intel.com>
Cc: Chandana Kumar <chandana.c.kumar@intel.com>
Cc: Kevin Li <kevin.y.li@intel.com>
Signed-off-by: Star Zeng <star.zeng@intel.com>
---
 .../CpuFeaturesInitialize.c                   | 10 +++--
 .../DxeRegisterCpuFeaturesLib.c               | 43 +++++++++++--------
 .../PeiRegisterCpuFeaturesLib.c               | 11 +++--
 3 files changed, 37 insertions(+), 27 deletions(-)

diff --git a/UefiCpuPkg/Library/RegisterCpuFeaturesLib/CpuFeaturesInitialize.c b/UefiCpuPkg/Library/RegisterCpuFeaturesLib/CpuFeaturesInitialize.c
index aff7ad600cad..1746f4f07f7b 100644
--- a/UefiCpuPkg/Library/RegisterCpuFeaturesLib/CpuFeaturesInitialize.c
+++ b/UefiCpuPkg/Library/RegisterCpuFeaturesLib/CpuFeaturesInitialize.c
@@ -1071,10 +1071,12 @@ CpuFeaturesDetect (
 
   CpuInitDataInitialize ();
 
-  //
-  // Wakeup all APs for data collection.
-  //
-  StartupAPsWorker (CollectProcessorData, NULL);
+  if (CpuFeaturesData->NumberOfCpus > 1) {
+    //
+    // Wakeup all APs for data collection.
+    //
+    StartupAPsWorker (CollectProcessorData, NULL);
+  }
 
   //
   // Collect data on BSP
diff --git a/UefiCpuPkg/Library/RegisterCpuFeaturesLib/DxeRegisterCpuFeaturesLib.c b/UefiCpuPkg/Library/RegisterCpuFeaturesLib/DxeRegisterCpuFeaturesLib.c
index 9c78a2d993c4..ffd99046a6cd 100644
--- a/UefiCpuPkg/Library/RegisterCpuFeaturesLib/DxeRegisterCpuFeaturesLib.c
+++ b/UefiCpuPkg/Library/RegisterCpuFeaturesLib/DxeRegisterCpuFeaturesLib.c
@@ -229,31 +229,36 @@ CpuFeaturesInitialize (
   OldBspNumber = GetProcessorIndex (CpuFeaturesData);
   CpuFeaturesData->BspNumber = OldBspNumber;
 
-  Status = gBS->CreateEvent (
-                  EVT_NOTIFY_WAIT,
-                  TPL_CALLBACK,
-                  EfiEventEmptyFunction,
-                  NULL,
-                  &MpEvent
-                  );
-  ASSERT_EFI_ERROR (Status);
+  if (CpuFeaturesData->NumberOfCpus > 1) {
+    Status = gBS->CreateEvent (
+                    EVT_NOTIFY_WAIT,
+                    TPL_CALLBACK,
+                    EfiEventEmptyFunction,
+                    NULL,
+                    &MpEvent
+                    );
+    ASSERT_EFI_ERROR (Status);
+
+    //
+    // Wakeup all APs for programming.
+    //
+    StartupAPsWorker (SetProcessorRegister, MpEvent);
+  }
 
-  //
-  // Wakeup all APs for programming.
-  //
-  StartupAPsWorker (SetProcessorRegister, MpEvent);
   //
   // Programming BSP
   //
   SetProcessorRegister (CpuFeaturesData);
 
-  //
-  // Wait all processors to finish the task.
-  //
-  do {
-    Status = gBS->CheckEvent (MpEvent);
-  } while (Status == EFI_NOT_READY);
-  ASSERT_EFI_ERROR (Status);
+  if (CpuFeaturesData->NumberOfCpus > 1) {
+    //
+    // Wait all processors to finish the task.
+    //
+    do {
+      Status = gBS->CheckEvent (MpEvent);
+    } while (Status == EFI_NOT_READY);
+    ASSERT_EFI_ERROR (Status);
+  }
 
   //
   // Switch to new BSP if required
diff --git a/UefiCpuPkg/Library/RegisterCpuFeaturesLib/PeiRegisterCpuFeaturesLib.c b/UefiCpuPkg/Library/RegisterCpuFeaturesLib/PeiRegisterCpuFeaturesLib.c
index 2b1553f9b84b..8ad5a40e5a44 100644
--- a/UefiCpuPkg/Library/RegisterCpuFeaturesLib/PeiRegisterCpuFeaturesLib.c
+++ b/UefiCpuPkg/Library/RegisterCpuFeaturesLib/PeiRegisterCpuFeaturesLib.c
@@ -273,10 +273,13 @@ CpuFeaturesInitialize (
   // DXE type instance.
   //
 
-  //
-  // Wakeup all APs for programming.
-  //
-  StartupAPsWorker (SetProcessorRegister, NULL);
+  if (CpuFeaturesData->NumberOfCpus > 1) {
+    //
+    // Wakeup all APs for programming.
+    //
+    StartupAPsWorker (SetProcessorRegister, NULL);
+  }
+
   //
   // Programming BSP
   //
-- 
2.21.0.windows.1