Advertise OVMF support for CPU hot-unplug and negotiate it
if QEMU requests the feature.

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 the following review comments:
    (1,3) s/hot unplug/hot-unplug/
    (2) Get rid of the reference to the made up ICH9_APM_CNT_CPU_HOT_UNPLUG
    (4,6) Remove the artificial tie in between
     ICH9_LPC_SMI_F_CPU_HOTPLUG, ICH9_LPC_SMI_F_CPU_HOT_UNPLUG.
    (5) Fully spell out "SMI on CPU hot-unplug".
    (7) Emit separate messages on negotiation (or not) of
     ICH9_LPC_SMI_F_CPU_HOT_UNPLUG.

 OvmfPkg/SmmControl2Dxe/SmiFeatures.c | 18 +++++++++++++++++-
 1 file changed, 17 insertions(+), 1 deletion(-)

diff --git a/OvmfPkg/SmmControl2Dxe/SmiFeatures.c b/OvmfPkg/SmmControl2Dxe/SmiFeatures.c
index c9d875543205..b1d59a559dae 100644
--- a/OvmfPkg/SmmControl2Dxe/SmiFeatures.c
+++ b/OvmfPkg/SmmControl2Dxe/SmiFeatures.c
@@ -29,6 +29,12 @@
 //
 #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_HOTPLUG upon hot-unplug", in the
+// "etc/smi/supported-features" and "etc/smi/requested-features" fw_cfg files.
+//
+#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.
@@ -112,7 +118,8 @@ NegotiateSmiFeatures (
   QemuFwCfgReadBytes (sizeof mSmiFeatures, &mSmiFeatures);
 
   //
-  // We want broadcast SMI, SMI on CPU hotplug, and nothing else.
+  // We want broadcast SMI, SMI on CPU hotplug, SMI on CPU hot-unplug
+  // and nothing else.
   //
   RequestedFeaturesMask = ICH9_LPC_SMI_F_BROADCAST;
   if (!MemEncryptSevIsEnabled ()) {
@@ -120,8 +127,10 @@ 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;
+
   QemuFwCfgSelectItem (mRequestedFeaturesItem);
   QemuFwCfgWriteBytes (sizeof mSmiFeatures, &mSmiFeatures);
 
@@ -166,6 +175,13 @@ NegotiateSmiFeatures (
       __FUNCTION__));
   }
 
+  if ((mSmiFeatures & ICH9_LPC_SMI_F_CPU_HOT_UNPLUG) == 0) {
+    DEBUG ((DEBUG_INFO, "%a: CPU hot-unplug not negotiated\n", __FUNCTION__));
+  } else {
+    DEBUG ((DEBUG_INFO, "%a: CPU hot-unplug with SMI negotiated\n",
+      __FUNCTION__));
+  }
+
   //
   // Negotiation successful (although we may not have gotten the optimal
   // feature set).
-- 
2.9.3



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