[PATCH V3 20/29] OvmfPkg: Check Tdx in QemuFwCfgPei to avoid DMA operation

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

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

If TDX is enabled then we do not support DMA operation in PEI phase.
This is mainly because DMA in TDX guest requires using bounce buffer
(which need to allocate dynamic memory and allocating a PAGE size'd
buffer can be challenge in PEI phase).

Cc: Ard Biesheuvel <ardb+tianocore@kernel.org>
Cc: Jordan Justen <jordan.l.justen@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>
Cc: Gerd Hoffmann <kraxel@redhat.com>
Signed-off-by: Min Xu <min.m.xu@intel.com>
---
 .../QemuFwCfgLib/QemuFwCfgLibInternal.h       | 11 +++++++
 OvmfPkg/Library/QemuFwCfgLib/QemuFwCfgPei.c   | 32 +++++++++++++++++++
 .../Library/QemuFwCfgLib/QemuFwCfgPeiLib.inf  |  2 ++
 3 files changed, 45 insertions(+)

diff --git a/OvmfPkg/Library/QemuFwCfgLib/QemuFwCfgLibInternal.h b/OvmfPkg/Library/QemuFwCfgLib/QemuFwCfgLibInternal.h
index 1fa80686e0bd..1130552bc60a 100644
--- a/OvmfPkg/Library/QemuFwCfgLib/QemuFwCfgLibInternal.h
+++ b/OvmfPkg/Library/QemuFwCfgLib/QemuFwCfgLibInternal.h
@@ -60,4 +60,15 @@ InternalQemuFwCfgDmaBytes (
   IN     UINT32   Control
   );
 
+/**
+  Check if it is Tdx guest
+
+  @retval    TRUE   It is Tdx guest
+  @retval    FALSE  It is not Tdx guest
+**/
+BOOLEAN
+QemuFwCfgIsTdxGuest (
+  VOID
+  );
+
 #endif
diff --git a/OvmfPkg/Library/QemuFwCfgLib/QemuFwCfgPei.c b/OvmfPkg/Library/QemuFwCfgLib/QemuFwCfgPei.c
index ecabd88fab66..bd2e51363bc6 100644
--- a/OvmfPkg/Library/QemuFwCfgLib/QemuFwCfgPei.c
+++ b/OvmfPkg/Library/QemuFwCfgLib/QemuFwCfgPei.c
@@ -14,12 +14,30 @@
 #include <Library/DebugLib.h>
 #include <Library/QemuFwCfgLib.h>
 #include <Library/MemEncryptSevLib.h>
+#include <WorkArea.h>
 
 #include "QemuFwCfgLibInternal.h"
 
 STATIC BOOLEAN mQemuFwCfgSupported = FALSE;
 STATIC BOOLEAN mQemuFwCfgDmaSupported;
 
+/**
+  Check if it is Tdx guest
+
+  @retval    TRUE   It is Tdx guest
+  @retval    FALSE  It is not Tdx guest
+**/
+BOOLEAN
+QemuFwCfgIsTdxGuest (
+  VOID
+  )
+{
+  CONFIDENTIAL_COMPUTING_WORK_AREA_HEADER   *CcWorkAreaHeader;
+
+  CcWorkAreaHeader = (CONFIDENTIAL_COMPUTING_WORK_AREA_HEADER *) FixedPcdGet32 (PcdOvmfWorkAreaBase);
+  return (CcWorkAreaHeader != NULL && CcWorkAreaHeader->GuestType == GUEST_TYPE_INTEL_TDX);
+}
+
 
 /**
   Returns a boolean indicating if the firmware configuration interface
@@ -82,6 +100,14 @@ QemuFwCfgInitialize (
     //
     if (MemEncryptSevIsEnabled ()) {
       DEBUG ((DEBUG_INFO, "SEV: QemuFwCfg fallback to IO Port interface.\n"));
+    } else if (QemuFwCfgIsTdxGuest ()) {
+      //
+      // If TDX is enabled then we do not support DMA operations in PEI phase.
+      // This is mainly because DMA in TDX guest requires using bounce buffer
+      // (which need to allocate dynamic memory and allocating a PAGE size'd
+      // buffer can be challenge in PEI phase)
+      //
+      DEBUG ((DEBUG_INFO, "TDX: QemuFwCfg fallback to IO Port interface.\n"));
     } else {
       mQemuFwCfgDmaSupported = TRUE;
       DEBUG ((DEBUG_INFO, "QemuFwCfg interface (DMA) is supported.\n"));
@@ -162,6 +188,12 @@ InternalQemuFwCfgDmaBytes (
   //
   ASSERT (!MemEncryptSevIsEnabled ());
 
+  //
+  // TDX does not support DMA operations in PEI stage, we should
+  // not have reached here.
+  //
+  ASSERT (!QemuFwCfgIsTdxGuest ());
+
   Access.Control = SwapBytes32 (Control);
   Access.Length  = SwapBytes32 (Size);
   Access.Address = SwapBytes64 ((UINTN)Buffer);
diff --git a/OvmfPkg/Library/QemuFwCfgLib/QemuFwCfgPeiLib.inf b/OvmfPkg/Library/QemuFwCfgLib/QemuFwCfgPeiLib.inf
index 9f9af7d03201..3910511880c9 100644
--- a/OvmfPkg/Library/QemuFwCfgLib/QemuFwCfgPeiLib.inf
+++ b/OvmfPkg/Library/QemuFwCfgLib/QemuFwCfgPeiLib.inf
@@ -43,3 +43,5 @@
   MemoryAllocationLib
   MemEncryptSevLib
 
+[Pcd]
+  gUefiOvmfPkgTokenSpaceGuid.PcdOvmfWorkAreaBase
-- 
2.29.2.windows.2