[RFC PATCH 5/5] OvmfPkg/SmmControl2Dxe: negotiate ICH9_LPC_SMI_F_CPU_HOT_UNPLUG

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

We treat ICH9_LPC_SMI_F_CPU_HOT_UNPLUG as a subset of the
ICH9_LPC_SMI_F_CPU_HOTPLUG feature flag.

Signed-off-by: Ankur Arora <ankur.a.arora@oracle.com>
---
 OvmfPkg/CpuHotplugSmm/CpuHotplug.c   |  5 -----
 OvmfPkg/SmmControl2Dxe/SmiFeatures.c | 21 +++++++++++++++++++--
 2 files changed, 19 insertions(+), 7 deletions(-)

diff --git a/OvmfPkg/CpuHotplugSmm/CpuHotplug.c b/OvmfPkg/CpuHotplugSmm/CpuHotplug.c
index 0a839ae52215..cdf8e55b8d91 100644
--- a/OvmfPkg/CpuHotplugSmm/CpuHotplug.c
+++ b/OvmfPkg/CpuHotplugSmm/CpuHotplug.c
@@ -367,11 +367,6 @@ CpuHotplugMmi (
   if (EFI_ERROR (Status)) {
     goto Fatal;
   }
-  if (ToUnplugCount > 0) {
-    DEBUG ((DEBUG_ERROR, "%a: hot-unplug is not supported yet\n",
-      __FUNCTION__));
-    goto Fatal;
-  }
 
   if (PluggedCount > 0) {
     Status = PlugCpus(mPluggedApicIds, PluggedCount);
diff --git a/OvmfPkg/SmmControl2Dxe/SmiFeatures.c b/OvmfPkg/SmmControl2Dxe/SmiFeatures.c
index c9d875543205..b95827051c2b 100644
--- a/OvmfPkg/SmmControl2Dxe/SmiFeatures.c
+++ b/OvmfPkg/SmmControl2Dxe/SmiFeatures.c
@@ -29,6 +29,13 @@
 //
 #define ICH9_LPC_SMI_F_CPU_HOTPLUG BIT1
 
+// The following bit value stands for "enable CPU hot unplug, and inject an SMI
+// with control value ICH9_APM_CNT_CPU_HOT_UNPLUG upon hot unplug", in the
+// "etc/smi/supported-features" and "etc/smi/requested-features" fw_cfg files.
+// Can only be negotiated alongside ICH9_LPC_SMI_F_CPU_HOTPLUG.
+//
+#define ICH9_LPC_SMI_F_CPU_HOT_UNPLUG BIT2
+
 //
 // Provides a scratch buffer (allocated in EfiReservedMemoryType type memory)
 // for the S3 boot script fragment to write to and read from.
@@ -120,8 +127,18 @@ NegotiateSmiFeatures (
     // For now, we only support hotplug with SEV disabled.
     //
     RequestedFeaturesMask |= ICH9_LPC_SMI_F_CPU_HOTPLUG;
+    RequestedFeaturesMask |= ICH9_LPC_SMI_F_CPU_HOT_UNPLUG;
   }
   mSmiFeatures &= RequestedFeaturesMask;
+
+  if (!(mSmiFeatures & ICH9_LPC_SMI_F_CPU_HOTPLUG) &&
+      (mSmiFeatures & ICH9_LPC_SMI_F_CPU_HOT_UNPLUG)) {
+    DEBUG ((DEBUG_WARN, "%a CPU host-feat %x, requested mask %Lx\n",
+      __FUNCTION__, mSmiFeatures, RequestedFeaturesMask));
+
+      mSmiFeatures &= ~ICH9_LPC_SMI_F_CPU_HOT_UNPLUG;
+  }
+
   QemuFwCfgSelectItem (mRequestedFeaturesItem);
   QemuFwCfgWriteBytes (sizeof mSmiFeatures, &mSmiFeatures);
 
@@ -162,8 +179,8 @@ NegotiateSmiFeatures (
   if ((mSmiFeatures & ICH9_LPC_SMI_F_CPU_HOTPLUG) == 0) {
     DEBUG ((DEBUG_INFO, "%a: CPU hotplug not negotiated\n", __FUNCTION__));
   } else {
-    DEBUG ((DEBUG_INFO, "%a: CPU hotplug with SMI negotiated\n",
-      __FUNCTION__));
+    DEBUG ((DEBUG_INFO, "%a: CPU hotplug%s with SMI negotiated\n",
+      __FUNCTION__, (mSmiFeatures & ICH9_LPC_SMI_F_CPU_HOT_UNPLUG) ? ", unplug" : ""));
   }
 
   //
-- 
2.25.4