From 7012cb73c473521e4fe4c997bfbfdfca0bd4b90c Mon Sep 17 00:00:00 2001
From: Min Xu <min.m.xu@intel.com>
Date: Tue, 19 Apr 2022 08:26:27 +0800
Subject: MdePkg: Probe Cc guest in BaseIoLibIntrinsicSev

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 CcProbe instead of TdIsEnabled in IsTdxGuest.
Null instance of CcProbe always returns CCGuestTypeNonEncrypted. Its
OvmfPkg version returns the guest type in Ovmf work area.

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>
Reviewed-by: Liming Gao <gaoliming@byosoft.com.cn>
Reviewed-by: Jiewen Yao <jiewen.yao@intel.com>
Reviewed-by: Tom Lendacky <thomas.lendacky@amd.com>
Signed-off-by: Min Xu <min.m.xu@intel.com>
---
 MdePkg/Library/BaseIoLibIntrinsic/BaseIoLibIntrinsicSev.inf |  1 +
 MdePkg/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 7fe1c60f04..e1b8298ac4 100644
--- a/MdePkg/Library/BaseIoLibIntrinsic/BaseIoLibIntrinsicSev.inf
+++ b/MdePkg/Library/BaseIoLibIntrinsic/BaseIoLibIntrinsicSev.inf
@@ -55,6 +55,7 @@
   DebugLib
   BaseLib
   RegisterFilterLib
+  CcProbeLib
 
 [LibraryClasses.X64]
   TdxLib
diff --git a/MdePkg/Library/BaseIoLibIntrinsic/IoLibInternalTdx.c b/MdePkg/Library/BaseIoLibIntrinsic/IoLibInternalTdx.c
index 1e539dbfbb..ec837f5eb0 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/CcProbeLib.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 CcProbe () == CcGuestTypeIntelTdx;
 }
 
 /**
-- 
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