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MdePkg: Probe Cc guest in BaseIoLibIntrinsicSev

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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>
This commit is contained in:
Min Xu 2022-04-19 08:26:27 +08:00 committed by mergify[bot]
parent 2a7e1e890d
commit 7012cb73c4
2 changed files with 3 additions and 11 deletions
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1
MdePkg/Library/BaseIoLibIntrinsic/BaseIoLibIntrinsicSev.inf
View File

@ -55,6 +55,7 @@
DebugLib
BaseLib
RegisterFilterLib
CcProbeLib
[LibraryClasses.X64]
TdxLib

13
MdePkg/Library/BaseIoLibIntrinsic/IoLibInternalTdx.c
View File

@ -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;
}
/**