[PATCH V2 5/6] MdePkg: Probe Cc guest in BaseIoLibIntrinsicSev

Min Xu

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@...>
Cc: Liming Gao <gaoliming@...>
Cc: Zhiguang Liu <zhiguang.liu@...>
Cc: James Bottomley <jejb@...>
Cc: James Bottomley <James.Bottomley@...>
Cc: Jiewen Yao <jiewen.yao@...>
Cc: Gerd Hoffmann <kraxel@...>
Signed-off-by: Min Xu <min.m.xu@...>
.../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..e1b8298ac451 100644
--- a/MdePkg/Library/BaseIoLibIntrinsic/BaseIoLibIntrinsicSev.inf
+++ b/MdePkg/Library/BaseIoLibIntrinsic/BaseIoLibIntrinsicSev.inf
@@ -55,6 +55,7 @@
+ CcProbeLib

diff --git a/MdePkg/Library/BaseIoLibIntrinsic/IoLibInternalTdx.c b/MdePkg/Library/BaseIoLibIntrinsic/IoLibInternalTdx.c
index 1e539dbfbbad..8af6fc35c591 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 @@

-BOOLEAN mTdxEnabled = FALSE;
-BOOLEAN mTdxProbed = FALSE;
Check if it is Tdx guest.

@@ -38,14 +36,7 @@ IsTdxGuest (
- if (mTdxProbed) {
- return mTdxEnabled;
- }
- mTdxEnabled = TdIsEnabled ();
- mTdxProbed = TRUE;
- return mTdxEnabled;
+ return CcProbe () == CCGuestTypeIntelTdx;


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