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>
---

Notes:
    Addresses these review comments from v6:
     (1) Drop the empty line in the comment block around UnplugCpus().
     (2) Make the "did not find APIC ID" DEBUG_VERBOSE instead of DEBUG_INFO.
     (3) Un-Indented ("Outdented") the line following the comment "Ignore the
      unplug if APIC ID.
     (4) Remove the empty line between Status assignment and check.
     (5) Drop the "goto Fatal" logic and just return Status directly.
     (6) Handle both Plugging and Unplugging of CPUs in one go.
     (7) Also nest the EFI_STATUS check.

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

diff --git a/OvmfPkg/CpuHotplugSmm/CpuHotplug.c b/OvmfPkg/CpuHotplugSmm/CpuHotplug.c
index 3192bfea1f15..f07b5072749a 100644
--- a/OvmfPkg/CpuHotplugSmm/CpuHotplug.c
+++ b/OvmfPkg/CpuHotplugSmm/CpuHotplug.c
@@ -188,6 +188,83 @@ 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_VERBOSE, "%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));
+      return Status;
+    }
+
+    ToUnplugIdx++;
+  }
+
+  //
+  // We've removed this set of APIC IDs from SMM data structures.
+  //
+  return EFI_SUCCESS;
+}
+
+/**
   CPU Hotplug MMI handler function.
 
   This is a root MMI handler.
@@ -309,6 +386,13 @@ CpuHotplugMmi (
     }
   }
 
+  if (ToUnplugCount > 0) {
+    Status = UnplugCpus (mToUnplugApicIds, ToUnplugCount);
+    if (EFI_ERROR (Status)) {
+      goto Fatal;
+    }
+  }
+
   //
   // We've handled this MMI.
   //
-- 
2.9.3



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