[edk2-devel] [PATCH V12 34/47] OvmfPkg: Check Tdx in QemuFwCfgPei to avoid DMA operation

[Min Xu]

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 at kernel.org>
Cc: Jordan Justen <jordan.l.justen at intel.com>
Cc: Brijesh Singh <brijesh.singh at amd.com>
Cc: Erdem Aktas <erdemaktas at google.com>
Cc: James Bottomley <jejb at linux.ibm.com>
Cc: Jiewen Yao <jiewen.yao at intel.com>
Cc: Tom Lendacky <thomas.lendacky at amd.com>
Cc: Gerd Hoffmann <kraxel at redhat.com>
Acked-by: Gerd Hoffmann <kraxel at redhat.com>
Signed-off-by: Min Xu <min.m.xu at 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 0b77cad1c030..6f7beb6ac1c7 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 f696fb7cacaa..b8230613dcea 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 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



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