[PATCH V2 20/28] MdeModulePkg: EFER should not be changed in TDX

["Min Xu" <min.m.xu@intel.com>]

RFC： https://bugzilla.tianocore.org/show_bug.cgi?id=3429

In TDX IA32_ERER is RO to host VMM. It could not be changed.
PcdIa32EferChangeAllowed is added in MdeModulePkg.dec and it is to be set
to FALSE in Tdx guest.

Cc: Jian J Wang <jian.j.wang@intel.com>
Cc: Hao A Wu <hao.a.wu@intel.com>
Cc: Brijesh Singh <brijesh.singh@amd.com>
Cc: Erdem Aktas <erdemaktas@google.com>
Cc: James Bottomley <jejb@linux.ibm.com>
Cc: Jiewen Yao <jiewen.yao@intel.com>
Cc: Tom Lendacky <thomas.lendacky@amd.com>
Signed-off-by: Min Xu <min.m.xu@intel.com>
---
 MdeModulePkg/Core/DxeIplPeim/DxeIpl.inf          | 1 +
 MdeModulePkg/Core/DxeIplPeim/X64/VirtualMemory.c | 6 ++++++
 MdeModulePkg/MdeModulePkg.dec                    | 5 +++++
 3 files changed, 12 insertions(+)

diff --git a/MdeModulePkg/Core/DxeIplPeim/DxeIpl.inf b/MdeModulePkg/Core/DxeIplPeim/DxeIpl.inf
index 19b8a4c8aefa..106b679b6bd0 100644
--- a/MdeModulePkg/Core/DxeIplPeim/DxeIpl.inf
+++ b/MdeModulePkg/Core/DxeIplPeim/DxeIpl.inf
@@ -117,6 +117,7 @@
   gEfiMdeModulePkgTokenSpaceGuid.PcdUse5LevelPageTable                  ## SOMETIMES_CONSUMES
   gEfiMdeModulePkgTokenSpaceGuid.PcdGhcbBase                            ## CONSUMES
   gEfiMdeModulePkgTokenSpaceGuid.PcdGhcbSize                            ## CONSUMES
+  gEfiMdeModulePkgTokenSpaceGuid.PcdIa32EferChangeAllowed               ## CONSUMES
 
 [Pcd.IA32,Pcd.X64,Pcd.ARM,Pcd.AARCH64]
   gEfiMdeModulePkgTokenSpaceGuid.PcdSetNxForStack               ## SOMETIMES_CONSUMES
diff --git a/MdeModulePkg/Core/DxeIplPeim/X64/VirtualMemory.c b/MdeModulePkg/Core/DxeIplPeim/X64/VirtualMemory.c
index 6831946c54d3..8a3b72509310 100644
--- a/MdeModulePkg/Core/DxeIplPeim/X64/VirtualMemory.c
+++ b/MdeModulePkg/Core/DxeIplPeim/X64/VirtualMemory.c
@@ -148,6 +148,12 @@ IsEnableNonExecNeeded (
     return FALSE;
   }
 
+  //
+  // Intel TDX sets this flag to FALSE.
+  //
+  if (!PcdGetBool (PcdIa32EferChangeAllowed)) {
+    return FALSE;
+  }
   //
   // XD flag (BIT63) in page table entry is only valid if IA32_EFER.NXE is set.
   // Features controlled by Following PCDs need this feature to be enabled.
diff --git a/MdeModulePkg/MdeModulePkg.dec b/MdeModulePkg/MdeModulePkg.dec
index 133e04ee86ca..007044a311c2 100644
--- a/MdeModulePkg/MdeModulePkg.dec
+++ b/MdeModulePkg/MdeModulePkg.dec
@@ -2138,6 +2138,11 @@
   # @Prompt GHCB Pool Size
   gEfiMdeModulePkgTokenSpaceGuid.PcdGhcbSize|0|UINT64|0x00030008
 
+  ## This dynamic PCD indicates if IA32_EFER can be changed. The default value is TRUE but in
+  #  Intel TDX change of IA32_EFER is not allowed.
+  # @Prompt The flag which indicates if IA32_EFER is allowed to be changed.
+  gEfiMdeModulePkgTokenSpaceGuid.PcdIa32EferChangeAllowed|TRUE|BOOLEAN|0x00030009
+
 [PcdsDynamicEx]
   ## This dynamic PCD enables the default variable setting.
   #  Its value is the default store ID value. The default value is zero as Standard default.
-- 
2.29.2.windows.2