[PATCH v2 2/2] UefiCpuPkg/MpInitLib: Decrease NumApsExecuting only for ApInitConfig

["Ni, Ray" <ray.ni@intel.com>]

The patch fixes the bug that the memory under 1MB is modified by
firmware in S3 boot.

Root cause is a racing condition in MpInitLib:
1. BSP: WakeUpByInitSipiSipi is set by NotifyOnS3SmmInitDonePpi()
2. BSP: WakeUpAP() wakes all APs to run certain procedure.
  2.1. AllocateResetVector() uses <1MB memory for wake up vector.
  2.1. FillExchangeInfoData() resets NumApsExecuting to 0.
  2.2. WaitApWakeup() waits AP to clear WAKEUP_AP_SIGNAL.
3. AP: ApWakeupFunction() clears WAKEUP_AP_SIGNAL to inform BSP.
5. BSP: FreeResetVector() restores the <1MB memory
4. AP: ApWakeupFunction() calls the certain procedure.
  4.1. NumApsExecuting is decreased.

#4.1 happens after the 1MB memory is restored so the result is
memory below 1MB is changed by #4.1
It happens only when the AP executes procedure a bit longer.
AP returns back to ApWakeupFunction() from procedure after
BSP restores the <1MB memory.

Since NumApsExecuting is only used when InitFlag == ApInitConfig
for counting the processor count.
The patch moves the NumApsExecuting decrease to the path when
InitFlag == ApInitConfig.

Signed-off-by: Ray Ni <ray.ni@intel.com>
Cc: Eric Dong <eric.dong@intel.com>
Cc: Nandagopal Sathyanarayanan <nandagopal.sathyanarayanan@intel.com>
---
 UefiCpuPkg/Library/MpInitLib/MpLib.c | 5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/UefiCpuPkg/Library/MpInitLib/MpLib.c b/UefiCpuPkg/Library/MpInitLib/MpLib.c
index 3337488892..6f51bc4ebf 100644
--- a/UefiCpuPkg/Library/MpInitLib/MpLib.c
+++ b/UefiCpuPkg/Library/MpInitLib/MpLib.c
@@ -1,7 +1,7 @@
 /** @file
   CPU MP Initialize Library common functions.
 
-  Copyright (c) 2016 - 2018, Intel Corporation. All rights reserved.<BR>
+  Copyright (c) 2016 - 2019, Intel Corporation. All rights reserved.<BR>
   SPDX-License-Identifier: BSD-2-Clause-Patent
 
 **/
@@ -619,6 +619,8 @@ ApWakeupFunction (
       RestoreVolatileRegisters (&CpuMpData->CpuData[0].VolatileRegisters, FALSE);
       InitializeApData (CpuMpData, ProcessorNumber, BistData, ApTopOfStack);
       ApStartupSignalBuffer = CpuMpData->CpuData[ProcessorNumber].StartupApSignal;
+
+      InterlockedDecrement ((UINT32 *) &CpuMpData->MpCpuExchangeInfo->NumApsExecuting);
     } else {
       //
       // Execute AP function if AP is ready
@@ -698,7 +700,6 @@ ApWakeupFunction (
     // AP finished executing C code
     //
     InterlockedIncrement ((UINT32 *) &CpuMpData->FinishedCount);
-    InterlockedDecrement ((UINT32 *) &CpuMpData->MpCpuExchangeInfo->NumApsExecuting);
 
     //
     // Place AP is specified loop mode
-- 
2.21.0.windows.1