[PATCH 3/4] MdePkg: Probe Td guest in BaseIoLibIntrinsicSev

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

BZ: https://bugzilla.tianocore.org/show_bug.cgi?id=3902

Bad IO performance in SEC phase is observed after TDX features was
introduced. (after commit b6b2de884864 - "MdePkg: Support mmio for
Tdx guest in BaseIoLibIntrinsic").

This is because IsTdxGuest() will be called in each MMIO operation.
It is trying to cache the result of the probe in the efi data segment.
However, that doesn't work in SEC, because the data segment is read only
(so the write seems to succeed but a read will always return the
original value), leading to us calling TdIsEnabled() check for every
mmio we do, which is causing the slowdown because it's very expensive.

This patch is to call TdProbe instead of IsTdxGuest. Null instance of
TdProbe returns TD_PROBE_NON anyway. Its OvmfPkg version checks the
Ovmf work area to determine the Td guest type.

Cc: Michael D Kinney <michael.d.kinney@intel.com>
Cc: Liming Gao <gaoliming@byosoft.com.cn>
Cc: Zhiguang Liu <zhiguang.liu@intel.com>
Cc: James Bottomley <jejb@linux.ibm.com>
Cc: James Bottomley <James.Bottomley@HansenPartnership.com>
Cc: Jiewen Yao <jiewen.yao@intel.com>
Cc: Gerd Hoffmann <kraxel@redhat.com>
Signed-off-by: Min Xu <min.m.xu@intel.com>
---
 .../BaseIoLibIntrinsic/BaseIoLibIntrinsicSev.inf    |  1 +
 .../Library/BaseIoLibIntrinsic/IoLibInternalTdx.c   | 13 ++-----------
 2 files changed, 3 insertions(+), 11 deletions(-)

diff --git a/MdePkg/Library/BaseIoLibIntrinsic/BaseIoLibIntrinsicSev.inf b/MdePkg/Library/BaseIoLibIntrinsic/BaseIoLibIntrinsicSev.inf
index 7fe1c60f046e..76f11438f40b 100644
--- a/MdePkg/Library/BaseIoLibIntrinsic/BaseIoLibIntrinsicSev.inf
+++ b/MdePkg/Library/BaseIoLibIntrinsic/BaseIoLibIntrinsicSev.inf
@@ -55,6 +55,7 @@
   DebugLib
   BaseLib
   RegisterFilterLib
+  TdProbeLib
 
 [LibraryClasses.X64]
   TdxLib
diff --git a/MdePkg/Library/BaseIoLibIntrinsic/IoLibInternalTdx.c b/MdePkg/Library/BaseIoLibIntrinsic/IoLibInternalTdx.c
index 1e539dbfbbad..9aed9f312858 100644
--- a/MdePkg/Library/BaseIoLibIntrinsic/IoLibInternalTdx.c
+++ b/MdePkg/Library/BaseIoLibIntrinsic/IoLibInternalTdx.c
@@ -10,6 +10,7 @@
 #include <Include/IndustryStandard/Tdx.h>
 #include <Library/TdxLib.h>
 #include <Register/Intel/Cpuid.h>
+#include <Library/TdProbeLib.h>
 #include "IoLibTdx.h"
 
 // Size of TDVMCALL Access, including IO and MMIO
@@ -22,9 +23,6 @@
 #define TDVMCALL_ACCESS_READ   0
 #define TDVMCALL_ACCESS_WRITE  1
 
-BOOLEAN  mTdxEnabled = FALSE;
-BOOLEAN  mTdxProbed  = FALSE;
-
 /**
   Check if it is Tdx guest.
 
@@ -38,14 +36,7 @@ IsTdxGuest (
   VOID
   )
 {
-  if (mTdxProbed) {
-    return mTdxEnabled;
-  }
-
-  mTdxEnabled = TdIsEnabled ();
-  mTdxProbed  = TRUE;
-
-  return mTdxEnabled;
+  return TdProbe () == TD_PROBE_TDX;
 }
 
 /**
-- 
2.29.2.windows.2