From 6b27c11690e7c093fa5670e854d10308c847a75d Mon Sep 17 00:00:00 2001
From: Min Xu <min.m.xu@intel.com>
Date: Mon, 19 Jul 2021 09:08:59 +0800
Subject: [PATCH] OvmfPkg: Check Tdx in QemuFwCfgPei to avoid DMA operation
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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>
Acked-by: Gerd Hoffmann <kraxel@redhat.com>
Reviewed-by: Jiewen Yao <jiewen.yao@intel.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 0b77cad1c0..6f7beb6ac1 100644
--- a/OvmfPkg/Library/QemuFwCfgLib/QemuFwCfgLibInternal.h
+++ b/OvmfPkg/Library/QemuFwCfgLib/QemuFwCfgLibInternal.h
@@ -59,4 +59,15 @@ 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 f696fb7cac..b8230613dc 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
   is available or not.
@@ -81,6 +99,14 @@ 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"));
@@ -163,6 +189,12 @@ 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 9f9af7d032..3910511880 100644
--- a/OvmfPkg/Library/QemuFwCfgLib/QemuFwCfgPeiLib.inf
+++ b/OvmfPkg/Library/QemuFwCfgLib/QemuFwCfgPeiLib.inf
@@ -43,3 +43,5 @@
   MemoryAllocationLib
   MemEncryptSevLib
 
+[Pcd]
+  gUefiOvmfPkgTokenSpaceGuid.PcdOvmfWorkAreaBase