From 43d696a3667a808dbe9117cf8131dbfa64dcf631 Mon Sep 17 00:00:00 2001
From: Laszlo Ersek <laszlo.ersek@posteo.net>
Date: Thu, 3 Jul 2025 20:34:03 +0200
Subject: [PATCH] OvmfPkg/CpuHotplugSmm: hook up MSR_IA32_FEATURE_CONTROL with
 platform info

Map the feature control MSR config from the OVMF platform info HOB to
FIRST_SMI_HANDLER_CONTEXT.

(Note that CpuHotplugSmm already consumes -- indirectly -- the
"MdePkg/Library/DxeHobLib/DxeHobLib.inf" library instance, according to
the build report; therefore adding an explicit HobLib class dependency
shouldn't *generally* increase this SMM driver's exposure. The consumed
lib instances are the same before and after this patch, at least in
"OvmfPkgIa32X64.dsc".)

Fixes: https://github.com/tianocore/edk2/issues/11188
Signed-off-by: Laszlo Ersek <laszlo.ersek@posteo.net>
---
 OvmfPkg/CpuHotplugSmm/CpuHotplugSmm.inf |  4 ++++
 OvmfPkg/CpuHotplugSmm/Smbase.c          | 21 ++++++++++++++++++++-
 2 files changed, 24 insertions(+), 1 deletion(-)

diff --git a/OvmfPkg/CpuHotplugSmm/CpuHotplugSmm.inf b/OvmfPkg/CpuHotplugSmm/CpuHotplugSmm.inf
index ebcc7e2ac6..0996968016 100644
--- a/OvmfPkg/CpuHotplugSmm/CpuHotplugSmm.inf
+++ b/OvmfPkg/CpuHotplugSmm/CpuHotplugSmm.inf
@@ -42,6 +42,7 @@
   BaseMemoryLib
   CpuLib
   DebugLib
+  HobLib
   LocalApicLib
   MmServicesTableLib
   PcdLib
@@ -53,6 +54,9 @@
   gEfiMmCpuIoProtocolGuid                                           ## CONSUMES
   gEfiSmmCpuServiceProtocolGuid                                     ## CONSUMES
 
+[Guids]
+  gUefiOvmfPkgPlatformInfoGuid                                      ## CONSUMES
+
 [Pcd]
   gUefiCpuPkgTokenSpaceGuid.PcdCpuHotPlugDataAddress                ## CONSUMES
   gUefiOvmfPkgTokenSpaceGuid.PcdCpuHotEjectDataAddress              ## CONSUMES
diff --git a/OvmfPkg/CpuHotplugSmm/Smbase.c b/OvmfPkg/CpuHotplugSmm/Smbase.c
index 2fd3ffb0b0..433633df98 100644
--- a/OvmfPkg/CpuHotplugSmm/Smbase.c
+++ b/OvmfPkg/CpuHotplugSmm/Smbase.c
@@ -10,7 +10,9 @@
 #include <Library/BaseLib.h>                  // CpuPause()
 #include <Library/BaseMemoryLib.h>            // CopyMem()
 #include <Library/DebugLib.h>                 // DEBUG()
+#include <Library/HobLib.h>                   // GetFirstGuidHob()
 #include <Library/LocalApicLib.h>             // SendInitSipiSipi()
+#include <Library/PlatformInitLib.h>          // EFI_HOB_PLATFORM_INFO
 #include <Library/SynchronizationLib.h>       // InterlockedCompareExchange64()
 #include <Register/Intel/SmramSaveStateMap.h> // SMM_DEFAULT_SMBASE
 
@@ -133,7 +135,9 @@ SmbaseReleasePostSmmPen (
   Note that this effects an "SMRAM to SMRAM" copy.
 
   Additionally, shut the APIC ID gate in FIRST_SMI_HANDLER_CONTEXT, and prepare
-  for configuring MSR_IA32_FEATURE_CONTROL.
+  for configuring MSR_IA32_FEATURE_CONTROL. (The latter depends on a GUID HOB,
+  which does not live in SMRAM; however, if we can't trust the HOB list at this
+  stage, we're doomed anyway.)
 
   This function may only be called from the entry point function of the driver,
   and only after PcdQ35SmramAtDefaultSmbase has been determined to be TRUE.
@@ -144,6 +148,7 @@ SmbaseInstallFirstSmiHandler (
   )
 {
   FIRST_SMI_HANDLER_CONTEXT  *Context;
+  EFI_HOB_GUID_TYPE          *GuidHob;
 
   CopyMem (
     (VOID *)(UINTN)(SMM_DEFAULT_SMBASE + SMM_HANDLER_OFFSET),
@@ -155,6 +160,20 @@ SmbaseInstallFirstSmiHandler (
   Context->ApicIdGate = MAX_UINT64;
 
   Context->FeatureControl = 0;
+  GuidHob                 = GetFirstGuidHob (&gUefiOvmfPkgPlatformInfoGuid);
+  if (GuidHob != NULL) {
+    EFI_HOB_PLATFORM_INFO  *Info;
+
+    Info = GET_GUID_HOB_DATA (GuidHob);
+    if (Info->FeatureControl) {
+      Context->FeatureControlHighValue = (UINT32)RShiftU64 (
+                                                   Info->FeatureControlValue,
+                                                   32
+                                                   );
+      Context->FeatureControlLowValue = (UINT32)Info->FeatureControlValue;
+      Context->FeatureControl         = 1;
+    }
+  }
 }
 
 /**