UefiCpuPkg/PiSmmCpuDxeSmm: Clarification for BSP & APs Sync Flow

(cherry picked from commit 2351165)

This patch does not impact functionality. It aims to clarify the
synchronization flow between the BSP and APs to enhance code
readability and understanding:

Steps tianocore#6 and tianocore#11 are the basic synchronization requirements for all
cases.

Steps #1 is additional requirements if the MmCpuSyncModeTradition
mode is selected.

Steps #1, #2, #3, tianocore#4, tianocore#5, tianocore#7, tianocore#8, tianocore#9, and tianocore#10 are additional
requirements if the system needs to configure the MTRR.

Steps tianocore#9 and tianocore#10 are additional requirements if the system needs to
support the mSmmDebugAgentSupport.

Signed-off-by: Jiaxin Wu <[email protected]>
(cherry picked from commit 2351165)

Change-Id: I3ca754e0b3f8c371e552e345483955a8016e786e

Author: jiaxinwu

UefiCpuPkg/PiSmmCpuDxeSmm/MpService.c

@@ -522,13 +522,13 @@ BSPHandler (
     //
     // Wait for all APs to get ready for programming MTRRs
     //
-    SmmCpuSyncWaitForAPs (mSmmMpSyncData->SyncContext, ApCount, CpuIndex);
+    SmmCpuSyncWaitForAPs (mSmmMpSyncData->SyncContext, ApCount, CpuIndex); /// #1: Wait APs
 
     if (SmmCpuFeaturesNeedConfigureMtrrs ()) {
       //
       // Signal all APs it's time for backup MTRRs
       //
-      ReleaseAllAPs ();
+      ReleaseAllAPs (); /// #2: Signal APs
 
       //
       // SmmCpuSyncWaitForAPs() may wait for ever if an AP happens to enter SMM at
@@ -543,12 +543,12 @@ BSPHandler (
       //
       // Wait for all APs to complete their MTRR saving
       //
-      SmmCpuSyncWaitForAPs (mSmmMpSyncData->SyncContext, ApCount, CpuIndex);
+      SmmCpuSyncWaitForAPs (mSmmMpSyncData->SyncContext, ApCount, CpuIndex); /// #3: Wait APs
 
       //
       // Let all processors program SMM MTRRs together
       //
-      ReleaseAllAPs ();
+      ReleaseAllAPs (); /// #4: Signal APs
 
       //
       // SmmCpuSyncWaitForAPs() may wait for ever if an AP happens to enter SMM at
@@ -560,7 +560,7 @@ BSPHandler (
       //
       // Wait for all APs to complete their MTRR programming
       //
-      SmmCpuSyncWaitForAPs (mSmmMpSyncData->SyncContext, ApCount, CpuIndex);
+      SmmCpuSyncWaitForAPs (mSmmMpSyncData->SyncContext, ApCount, CpuIndex); /// #5: Wait APs
     }
   }
 
@@ -625,18 +625,18 @@ BSPHandler (
   // Notify all APs to exit
   //
   *mSmmMpSyncData->InsideSmm = FALSE;
-  ReleaseAllAPs ();
+  ReleaseAllAPs (); /// #6: Signal APs
 
   if (SmmCpuFeaturesNeedConfigureMtrrs ()) {
     //
     // Wait for all APs the readiness to program MTRRs
     //
-    SmmCpuSyncWaitForAPs (mSmmMpSyncData->SyncContext, ApCount, CpuIndex);
+    SmmCpuSyncWaitForAPs (mSmmMpSyncData->SyncContext, ApCount, CpuIndex); /// #7: Wait APs
 
     //
     // Signal APs to restore MTRRs
     //
-    ReleaseAllAPs ();
+    ReleaseAllAPs (); /// #8: Signal APs
 
     //
     // Restore OS MTRRs
@@ -649,12 +649,12 @@ BSPHandler (
     //
     // Wait for all APs to complete their pending tasks including MTRR programming if needed.
     //
-    SmmCpuSyncWaitForAPs (mSmmMpSyncData->SyncContext, ApCount, CpuIndex);
+    SmmCpuSyncWaitForAPs (mSmmMpSyncData->SyncContext, ApCount, CpuIndex); /// #9: Wait APs
 
     //
     // Signal APs to Reset states/semaphore for this processor
     //
-    ReleaseAllAPs ();
+    ReleaseAllAPs (); /// #10: Signal APs
   }
 
   if (mSmmDebugAgentSupport) {
@@ -679,7 +679,7 @@ BSPHandler (
   // Gather APs to exit SMM synchronously. Note the Present flag is cleared by now but
   // WaitForAllAps does not depend on the Present flag.
   //
-  SmmCpuSyncWaitForAPs (mSmmMpSyncData->SyncContext, ApCount, CpuIndex);
+  SmmCpuSyncWaitForAPs (mSmmMpSyncData->SyncContext, ApCount, CpuIndex); /// #11: Wait APs
 
   //
   // At this point, all APs should have exited from APHandler().
@@ -805,14 +805,14 @@ APHandler (
     //
     // Notify BSP of arrival at this point
     //
-    SmmCpuSyncReleaseBsp (mSmmMpSyncData->SyncContext, CpuIndex, BspIndex);
+    SmmCpuSyncReleaseBsp (mSmmMpSyncData->SyncContext, CpuIndex, BspIndex); /// #1: Signal BSP
   }
 
   if (SmmCpuFeaturesNeedConfigureMtrrs ()) {
     //
     // Wait for the signal from BSP to backup MTRRs
     //
-    SmmCpuSyncWaitForBsp (mSmmMpSyncData->SyncContext, CpuIndex, BspIndex);
+    SmmCpuSyncWaitForBsp (mSmmMpSyncData->SyncContext, CpuIndex, BspIndex); /// #2: Wait BSP
 
     //
     // Backup OS MTRRs
@@ -822,12 +822,12 @@ APHandler (
     //
     // Signal BSP the completion of this AP
     //
-    SmmCpuSyncReleaseBsp (mSmmMpSyncData->SyncContext, CpuIndex, BspIndex);
+    SmmCpuSyncReleaseBsp (mSmmMpSyncData->SyncContext, CpuIndex, BspIndex); /// #3: Signal BSP
 
     //
     // Wait for BSP's signal to program MTRRs
     //
-    SmmCpuSyncWaitForBsp (mSmmMpSyncData->SyncContext, CpuIndex, BspIndex);
+    SmmCpuSyncWaitForBsp (mSmmMpSyncData->SyncContext, CpuIndex, BspIndex); /// #4: Wait BSP
 
     //
     // Replace OS MTRRs with SMI MTRRs
@@ -837,14 +837,14 @@ APHandler (
     //
     // Signal BSP the completion of this AP
     //
-    SmmCpuSyncReleaseBsp (mSmmMpSyncData->SyncContext, CpuIndex, BspIndex);
+    SmmCpuSyncReleaseBsp (mSmmMpSyncData->SyncContext, CpuIndex, BspIndex); /// #5: Signal BSP
   }
 
   while (TRUE) {
     //
     // Wait for something to happen
     //
-    SmmCpuSyncWaitForBsp (mSmmMpSyncData->SyncContext, CpuIndex, BspIndex);
+    SmmCpuSyncWaitForBsp (mSmmMpSyncData->SyncContext, CpuIndex, BspIndex); /// #6: Wait BSP
 
     //
     // Check if BSP wants to exit SMM
@@ -884,12 +884,12 @@ APHandler (
     //
     // Notify BSP the readiness of this AP to program MTRRs
     //
-    SmmCpuSyncReleaseBsp (mSmmMpSyncData->SyncContext, CpuIndex, BspIndex);
+    SmmCpuSyncReleaseBsp (mSmmMpSyncData->SyncContext, CpuIndex, BspIndex); /// #7: Signal BSP
 
     //
     // Wait for the signal from BSP to program MTRRs
     //
-    SmmCpuSyncWaitForBsp (mSmmMpSyncData->SyncContext, CpuIndex, BspIndex);
+    SmmCpuSyncWaitForBsp (mSmmMpSyncData->SyncContext, CpuIndex, BspIndex); /// #8: Wait BSP
 
     //
     // Restore OS MTRRs
@@ -902,12 +902,12 @@ APHandler (
     //
     // Notify BSP the readiness of this AP to Reset states/semaphore for this processor
     //
-    SmmCpuSyncReleaseBsp (mSmmMpSyncData->SyncContext, CpuIndex, BspIndex);
+    SmmCpuSyncReleaseBsp (mSmmMpSyncData->SyncContext, CpuIndex, BspIndex); /// #9: Signal BSP
 
     //
     // Wait for the signal from BSP to Reset states/semaphore for this processor
     //
-    SmmCpuSyncWaitForBsp (mSmmMpSyncData->SyncContext, CpuIndex, BspIndex);
+    SmmCpuSyncWaitForBsp (mSmmMpSyncData->SyncContext, CpuIndex, BspIndex); /// #10: Wait BSP
   }
 
   //
@@ -918,7 +918,7 @@ APHandler (
   //
   // Notify BSP the readiness of this AP to exit SMM
   //
-  SmmCpuSyncReleaseBsp (mSmmMpSyncData->SyncContext, CpuIndex, BspIndex);
+  SmmCpuSyncReleaseBsp (mSmmMpSyncData->SyncContext, CpuIndex, BspIndex); /// #11: Signal BSP
 }
 
 /**