[PATCH v6 1/9] OvmfPkg/CpuHotplugSmm: refactor hotplug logic

["Ankur Arora" <ankur.a.arora@oracle.com>]

Refactor CpuHotplugMmi() to pull out the CPU hotplug logic into
ProcessHotAddedCpus(). This is in preparation for supporting CPU
hot-unplug.

Cc: Laszlo Ersek <lersek@redhat.com>
Cc: Jordan Justen <jordan.l.justen@intel.com>
Cc: Ard Biesheuvel <ard.biesheuvel@arm.com>
Cc: Igor Mammedov <imammedo@redhat.com>
Cc: Boris Ostrovsky <boris.ostrovsky@oracle.com>
Cc: Aaron Young <aaron.young@oracle.com>
Ref: https://bugzilla.tianocore.org/show_bug.cgi?id=3132
Signed-off-by: Ankur Arora <ankur.a.arora@oracle.com>
---

Notes:
     > +  if (EFI_ERROR(Status)) {
     > +    goto Fatal;
     >    }
    
     (13) Without having seen the rest of the patches, I think this error
     check should be nested under the same (PluggedCount > 0) condition; in
     other words, I think it only makes sense to check Status after we
     actually call ProcessHotAddedCpus().
    
    Addresses all comments from v5, except for this one, since the (lack) of
    nesting makes more sense after patch 4, "OvmfPkg/CpuHotplugSmm: introduce
    UnplugCpus()".

 OvmfPkg/CpuHotplugSmm/CpuHotplug.c | 214 ++++++++++++++++++++++---------------
 1 file changed, 129 insertions(+), 85 deletions(-)

diff --git a/OvmfPkg/CpuHotplugSmm/CpuHotplug.c b/OvmfPkg/CpuHotplugSmm/CpuHotplug.c
index cfe698ed2b5e..05b1f8cb63a6 100644
--- a/OvmfPkg/CpuHotplugSmm/CpuHotplug.c
+++ b/OvmfPkg/CpuHotplugSmm/CpuHotplug.c
@@ -62,6 +62,130 @@ STATIC UINT32 mPostSmmPenAddress;
 //
 STATIC EFI_HANDLE mDispatchHandle;
 
+/**
+  Process CPUs that have been hot-added, per QemuCpuhpCollectApicIds().
+
+  For each such CPU, relocate the SMBASE, and report the CPU to PiSmmCpuDxeSmm
+  via EFI_SMM_CPU_SERVICE_PROTOCOL. If the supposedly hot-added CPU is already
+  known, skip it silently.
+
+  @param[in] PluggedApicIds    The APIC IDs of the CPUs that have been
+                               hot-plugged.
+
+  @param[in] PluggedCount      The number of filled-in APIC IDs in
+                               PluggedApicIds.
+
+  @retval EFI_SUCCESS          CPUs corresponding to all the APIC IDs are
+                               populated.
+
+  @retval EFI_OUT_OF_RESOURCES Out of APIC ID space in "mCpuHotPlugData".
+
+  @return                      Error codes propagated from SmbaseRelocate()
+                               and mMmCpuService->AddProcessor().
+
+**/
+STATIC
+EFI_STATUS
+ProcessHotAddedCpus (
+  IN APIC_ID                      *PluggedApicIds,
+  IN UINT32                       PluggedCount
+  )
+{
+  EFI_STATUS Status;
+  UINT32     PluggedIdx;
+  UINT32     NewSlot;
+
+  //
+  // The Post-SMM Pen need not be reinstalled multiple times within a single
+  // root MMI handling. Even reinstalling once per root MMI is only prudence;
+  // in theory installing the pen in the driver's entry point function should
+  // suffice.
+  //
+  SmbaseReinstallPostSmmPen (mPostSmmPenAddress);
+
+  PluggedIdx = 0;
+  NewSlot = 0;
+  while (PluggedIdx < PluggedCount) {
+    APIC_ID NewApicId;
+    UINT32  CheckSlot;
+    UINTN   NewProcessorNumberByProtocol;
+
+    NewApicId = PluggedApicIds[PluggedIdx];
+
+    //
+    // Check if the supposedly hot-added CPU is already known to us.
+    //
+    for (CheckSlot = 0;
+         CheckSlot < mCpuHotPlugData->ArrayLength;
+         CheckSlot++) {
+      if (mCpuHotPlugData->ApicId[CheckSlot] == NewApicId) {
+        break;
+      }
+    }
+    if (CheckSlot < mCpuHotPlugData->ArrayLength) {
+      DEBUG ((DEBUG_VERBOSE, "%a: APIC ID " FMT_APIC_ID " was hot-plugged "
+        "before; ignoring it\n", __FUNCTION__, NewApicId));
+      PluggedIdx++;
+      continue;
+    }
+
+    //
+    // Find the first empty slot in CPU_HOT_PLUG_DATA.
+    //
+    while (NewSlot < mCpuHotPlugData->ArrayLength &&
+           mCpuHotPlugData->ApicId[NewSlot] != MAX_UINT64) {
+      NewSlot++;
+    }
+    if (NewSlot == mCpuHotPlugData->ArrayLength) {
+      DEBUG ((DEBUG_ERROR, "%a: no room for APIC ID " FMT_APIC_ID "\n",
+        __FUNCTION__, NewApicId));
+      return EFI_OUT_OF_RESOURCES;
+    }
+
+    //
+    // Store the APIC ID of the new processor to the slot.
+    //
+    mCpuHotPlugData->ApicId[NewSlot] = NewApicId;
+
+    //
+    // Relocate the SMBASE of the new CPU.
+    //
+    Status = SmbaseRelocate (NewApicId, mCpuHotPlugData->SmBase[NewSlot],
+               mPostSmmPenAddress);
+    if (EFI_ERROR (Status)) {
+      goto RevokeNewSlot;
+    }
+
+    //
+    // Add the new CPU with EFI_SMM_CPU_SERVICE_PROTOCOL.
+    //
+    Status = mMmCpuService->AddProcessor (mMmCpuService, NewApicId,
+                              &NewProcessorNumberByProtocol);
+    if (EFI_ERROR (Status)) {
+      DEBUG ((DEBUG_ERROR, "%a: AddProcessor(" FMT_APIC_ID "): %r\n",
+        __FUNCTION__, NewApicId, Status));
+      goto RevokeNewSlot;
+    }
+
+    DEBUG ((DEBUG_INFO, "%a: hot-added APIC ID " FMT_APIC_ID ", SMBASE 0x%Lx, "
+      "EFI_SMM_CPU_SERVICE_PROTOCOL assigned number %Lu\n", __FUNCTION__,
+      NewApicId, (UINT64)mCpuHotPlugData->SmBase[NewSlot],
+      (UINT64)NewProcessorNumberByProtocol));
+
+    NewSlot++;
+    PluggedIdx++;
+  }
+
+  //
+  // We've processed this batch of hot-added CPUs.
+  //
+  return EFI_SUCCESS;
+
+RevokeNewSlot:
+  mCpuHotPlugData->ApicId[NewSlot] = MAX_UINT64;
+
+  return Status;
+}
 
 /**
   CPU Hotplug MMI handler function.
@@ -122,8 +246,6 @@ CpuHotplugMmi (
   UINT8      ApmControl;
   UINT32     PluggedCount;
   UINT32     ToUnplugCount;
-  UINT32     PluggedIdx;
-  UINT32     NewSlot;
 
   //
   // Assert that we are entering this function due to our root MMI handler
@@ -179,87 +301,12 @@ CpuHotplugMmi (
     goto Fatal;
   }
 
-  //
-  // Process hot-added CPUs.
-  //
-  // The Post-SMM Pen need not be reinstalled multiple times within a single
-  // root MMI handling. Even reinstalling once per root MMI is only prudence;
-  // in theory installing the pen in the driver's entry point function should
-  // suffice.
-  //
-  SmbaseReinstallPostSmmPen (mPostSmmPenAddress);
+  if (PluggedCount > 0) {
+    Status = ProcessHotAddedCpus (mPluggedApicIds, PluggedCount);
+  }
 
-  PluggedIdx = 0;
-  NewSlot = 0;
-  while (PluggedIdx < PluggedCount) {
-    APIC_ID NewApicId;
-    UINT32  CheckSlot;
-    UINTN   NewProcessorNumberByProtocol;
-
-    NewApicId = mPluggedApicIds[PluggedIdx];
-
-    //
-    // Check if the supposedly hot-added CPU is already known to us.
-    //
-    for (CheckSlot = 0;
-         CheckSlot < mCpuHotPlugData->ArrayLength;
-         CheckSlot++) {
-      if (mCpuHotPlugData->ApicId[CheckSlot] == NewApicId) {
-        break;
-      }
-    }
-    if (CheckSlot < mCpuHotPlugData->ArrayLength) {
-      DEBUG ((DEBUG_VERBOSE, "%a: APIC ID " FMT_APIC_ID " was hot-plugged "
-        "before; ignoring it\n", __FUNCTION__, NewApicId));
-      PluggedIdx++;
-      continue;
-    }
-
-    //
-    // Find the first empty slot in CPU_HOT_PLUG_DATA.
-    //
-    while (NewSlot < mCpuHotPlugData->ArrayLength &&
-           mCpuHotPlugData->ApicId[NewSlot] != MAX_UINT64) {
-      NewSlot++;
-    }
-    if (NewSlot == mCpuHotPlugData->ArrayLength) {
-      DEBUG ((DEBUG_ERROR, "%a: no room for APIC ID " FMT_APIC_ID "\n",
-        __FUNCTION__, NewApicId));
-      goto Fatal;
-    }
-
-    //
-    // Store the APIC ID of the new processor to the slot.
-    //
-    mCpuHotPlugData->ApicId[NewSlot] = NewApicId;
-
-    //
-    // Relocate the SMBASE of the new CPU.
-    //
-    Status = SmbaseRelocate (NewApicId, mCpuHotPlugData->SmBase[NewSlot],
-               mPostSmmPenAddress);
-    if (EFI_ERROR (Status)) {
-      goto RevokeNewSlot;
-    }
-
-    //
-    // Add the new CPU with EFI_SMM_CPU_SERVICE_PROTOCOL.
-    //
-    Status = mMmCpuService->AddProcessor (mMmCpuService, NewApicId,
-                              &NewProcessorNumberByProtocol);
-    if (EFI_ERROR (Status)) {
-      DEBUG ((DEBUG_ERROR, "%a: AddProcessor(" FMT_APIC_ID "): %r\n",
-        __FUNCTION__, NewApicId, Status));
-      goto RevokeNewSlot;
-    }
-
-    DEBUG ((DEBUG_INFO, "%a: hot-added APIC ID " FMT_APIC_ID ", SMBASE 0x%Lx, "
-      "EFI_SMM_CPU_SERVICE_PROTOCOL assigned number %Lu\n", __FUNCTION__,
-      NewApicId, (UINT64)mCpuHotPlugData->SmBase[NewSlot],
-      (UINT64)NewProcessorNumberByProtocol));
-
-    NewSlot++;
-    PluggedIdx++;
+  if (EFI_ERROR(Status)) {
+    goto Fatal;
   }
 
   //
@@ -267,9 +314,6 @@ CpuHotplugMmi (
   //
   return EFI_SUCCESS;
 
-RevokeNewSlot:
-  mCpuHotPlugData->ApicId[NewSlot] = MAX_UINT64;
-
 Fatal:
   ASSERT (FALSE);
   CpuDeadLoop ();
-- 
2.9.3