[PATCH v6 4/9] OvmfPkg/CpuHotplugSmm: introduce UnplugCpus()

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

Introduce UnplugCpus() which maps each APIC ID being unplugged
onto the hardware ID of the processor and informs PiSmmCpuDxeSmm
of removal by calling EFI_SMM_CPU_SERVICE_PROTOCOL.RemoveProcessor().

With this change we handle the first phase of unplug where we collect
the CPUs that need to be unplugged and mark them for removal in SMM
data structures.

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>
---
 OvmfPkg/CpuHotplugSmm/CpuHotplug.c | 84 ++++++++++++++++++++++++++++++++++++++
 1 file changed, 84 insertions(+)

diff --git a/OvmfPkg/CpuHotplugSmm/CpuHotplug.c b/OvmfPkg/CpuHotplugSmm/CpuHotplug.c
index 05b1f8cb63a6..70d69f6ed65b 100644
--- a/OvmfPkg/CpuHotplugSmm/CpuHotplug.c
+++ b/OvmfPkg/CpuHotplugSmm/CpuHotplug.c
@@ -188,6 +188,88 @@ RevokeNewSlot:
 }
 
 /**
+  Process to be hot-unplugged CPUs, per QemuCpuhpCollectApicIds().
+
+  For each such CPU, report the CPU to PiSmmCpuDxeSmm via
+  EFI_SMM_CPU_SERVICE_PROTOCOL. If the to be hot-unplugged CPU is
+  unknown, skip it silently.
+
+  @param[in] ToUnplugApicIds    The APIC IDs of the CPUs that are about to be
+                                hot-unplugged.
+
+  @param[in] ToUnplugCount      The number of filled-in APIC IDs in
+                                ToUnplugApicIds.
+
+  @retval EFI_SUCCESS           Known APIC IDs have been removed from SMM data
+                                structures.
+
+  @return                       Error codes propagated from
+                                mMmCpuService->RemoveProcessor().
+
+**/
+STATIC
+EFI_STATUS
+UnplugCpus (
+  IN APIC_ID                      *ToUnplugApicIds,
+  IN UINT32                       ToUnplugCount
+  )
+{
+  EFI_STATUS Status;
+  UINT32     ToUnplugIdx;
+  UINTN      ProcessorNum;
+
+  ToUnplugIdx = 0;
+  while (ToUnplugIdx < ToUnplugCount) {
+    APIC_ID    RemoveApicId;
+
+    RemoveApicId = ToUnplugApicIds[ToUnplugIdx];
+
+    //
+    // mCpuHotPlugData->ApicId maps ProcessorNum -> ApicId. Use it to find
+    // the ProcessorNum for the APIC ID to be removed.
+    //
+    for (ProcessorNum = 0;
+         ProcessorNum < mCpuHotPlugData->ArrayLength;
+         ProcessorNum++) {
+      if (mCpuHotPlugData->ApicId[ProcessorNum] == RemoveApicId) {
+        break;
+      }
+    }
+
+    //
+    // Ignore the unplug if APIC ID not found
+    //
+    if (ProcessorNum == mCpuHotPlugData->ArrayLength) {
+      DEBUG ((DEBUG_INFO, "%a: did not find APIC ID " FMT_APIC_ID
+          " to unplug\n", __FUNCTION__, RemoveApicId));
+      ToUnplugIdx++;
+      continue;
+    }
+
+    //
+    // Mark ProcessorNum for removal from SMM data structures
+    //
+    Status = mMmCpuService->RemoveProcessor (mMmCpuService, ProcessorNum);
+
+    if (EFI_ERROR (Status)) {
+      DEBUG ((DEBUG_ERROR, "%a: RemoveProcessor(" FMT_APIC_ID "): %r\n",
+        __FUNCTION__, RemoveApicId, Status));
+      goto Fatal;
+    }
+
+    ToUnplugIdx++;
+  }
+
+  //
+  // We've removed this set of APIC IDs from SMM data structures.
+  //
+  return EFI_SUCCESS;
+
+Fatal:
+  return Status;
+}
+
+/**
   CPU Hotplug MMI handler function.
 
   This is a root MMI handler.
@@ -303,6 +385,8 @@ CpuHotplugMmi (
 
   if (PluggedCount > 0) {
     Status = ProcessHotAddedCpus (mPluggedApicIds, PluggedCount);
+  } else if (ToUnplugCount > 0) {
+    Status = UnplugCpus (mToUnplugApicIds, ToUnplugCount);
   }
 
   if (EFI_ERROR(Status)) {
-- 
2.9.3