[PATCH v2 4/5] UefiCpuPkg/DxeMpLib: Fix bug when getting target C-State from eax

[Jeff Fan <jeff.fan@intel.com>]

AP will get target C-State from eax[7:4]. We do shift in ebx firstly before set
to eax. It will lead ebx is correct in the next time.

The fix is to set ebx to eax firstly and does shift in eax. Thus, ebx could keep
original value.

Reported-by: Laszlo Ersek <lersek@redhat.com>
Cc: Laszlo Ersek <lersek@redhat.com>
Cc: Feng Tian <feng.tian@intel.com>
Cc: Michael D Kinney <michael.d.kinney@intel.com>
Contributed-under: TianoCore Contribution Agreement 1.0
Signed-off-by: Jeff Fan <jeff.fan@intel.com>
---
 UefiCpuPkg/Library/MpInitLib/X64/MpFuncs.nasm | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/UefiCpuPkg/Library/MpInitLib/X64/MpFuncs.nasm b/UefiCpuPkg/Library/MpInitLib/X64/MpFuncs.nasm
index f8f4712..34c07a6 100644
--- a/UefiCpuPkg/Library/MpInitLib/X64/MpFuncs.nasm
+++ b/UefiCpuPkg/Library/MpInitLib/X64/MpFuncs.nasm
@@ -266,8 +266,8 @@ MwaitLoop:
     xor        ecx, ecx           ; ecx = 0
     xor        edx, edx           ; edx = 0
     monitor
-    shl        ebx, 4
     mov        eax, ebx           ; Mwait Cx, Target C-State per eax[7:4]
+    shl        eax, 4
     mwait
     jmp        MwaitLoop
 HltLoop:
-- 
2.9.3.windows.2