From 3a4ec6de01209a0310a6e4c63d6941e7a592a457 Mon Sep 17 00:00:00 2001
From: Jiaxin Wu <jiaxin.wu@intel.com>
Date: Fri, 15 Dec 2023 16:45:38 +0800
Subject: UefiCpuPkg/PiSmmCpuDxeSmm: Align BSP and AP sync logic for SMI exit

Below piece of code is the BSP and AP sync logic for SMI exit.
1. AP after finish the scheduled procedure:
  if (SmmCpuFeaturesNeedConfigureMtrrs ()) {
    SmmCpuSyncReleaseBsp ();
    SmmCpuSyncWaitForBsp ();
    ...
  }
  SmmCpuSyncReleaseBsp ();
  SmmCpuSyncWaitForBsp ();
  SmmCpuSyncReleaseBsp ();

2. BSP after return from SmmCoreEntry:
  SmmCpuSyncWaitForAPs ();
  if (SmmCpuFeaturesNeedConfigureMtrrs ()) {
    ReleaseAllAPs ();
    ...
    SmmCpuSyncWaitForAPs ();
  }
  ReleaseAllAPs ();
  SmmCpuSyncWaitForAPs();

This patch is to make BSP same as AP sync logic:
  if (SmmCpuFeaturesNeedConfigureMtrrs ()) {
    SmmCpuSyncWaitForAPs ();
    ReleaseAllAPs ();
    ...
  }
  SmmCpuSyncWaitForAPs ();
  ReleaseAllAPs ();
  SmmCpuSyncWaitForAPs();

With the change, it will be easy to understand the sync flow as
below:
BSP: SmmCpuSyncWaitForAPs  <--  AP: SmmCpuSyncReleaseBsp
BSP: ReleaseAllAPs         -->  AP: SmmCpuSyncWaitForBsp

This patch doesn't have function impact.

Cc: Laszlo Ersek <lersek@redhat.com>
Cc: Eric Dong <eric.dong@intel.com>
Cc: Ray Ni <ray.ni@intel.com>
Cc: Zeng Star <star.zeng@intel.com>
Cc: Gerd Hoffmann <kraxel@redhat.com>
Cc: Rahul Kumar <rahul1.kumar@intel.com>
Signed-off-by: Jiaxin Wu <jiaxin.wu@intel.com>
Reviewed-by: Ray Ni <ray.ni@Intel.com>
---
 UefiCpuPkg/PiSmmCpuDxeSmm/MpService.c | 20 ++++++++++----------
 1 file changed, 10 insertions(+), 10 deletions(-)

diff --git a/UefiCpuPkg/PiSmmCpuDxeSmm/MpService.c b/UefiCpuPkg/PiSmmCpuDxeSmm/MpService.c
index 324e85d6b5..bd2c9f841b 100644
--- a/UefiCpuPkg/PiSmmCpuDxeSmm/MpService.c
+++ b/UefiCpuPkg/PiSmmCpuDxeSmm/MpService.c
@@ -627,12 +627,12 @@ BSPHandler (
   *mSmmMpSyncData->InsideSmm = FALSE;
   ReleaseAllAPs ();
 
-  //
-  // Wait for all APs to complete their pending tasks
-  //
-  SmmCpuSyncWaitForAPs (mSmmMpSyncData->SyncContext, ApCount, CpuIndex);
-
   if (SmmCpuFeaturesNeedConfigureMtrrs ()) {
+    //
+    // Wait for all APs the readiness to program MTRRs
+    //
+    SmmCpuSyncWaitForAPs (mSmmMpSyncData->SyncContext, ApCount, CpuIndex);
+
     //
     // Signal APs to restore MTRRs
     //
@@ -643,13 +643,13 @@ BSPHandler (
     //
     SmmCpuFeaturesReenableSmrr ();
     MtrrSetAllMtrrs (&Mtrrs);
-
-    //
-    // Wait for all APs to complete MTRR programming
-    //
-    SmmCpuSyncWaitForAPs (mSmmMpSyncData->SyncContext, ApCount, CpuIndex);
   }
 
+  //
+  // Wait for all APs to complete their pending tasks including MTRR programming if needed.
+  //
+  SmmCpuSyncWaitForAPs (mSmmMpSyncData->SyncContext, ApCount, CpuIndex);
+
   if (mSmmDebugAgentSupport) {
     //
     // Stop source level debug in BSP handler, the code below will not be
-- 
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