[edk2: PATCH] UefiCpuPkg: To enable X2Apic by default

[Ji-yunX Lu <ji-yunx.lu@intel.com>]

BZ: https://bugzilla.tianocore.org/show_bug.cgi?id=2845
Platform shall enable X2APIC by default to meet requirements for interrupt steering policy on Windows OS.

Change-Id: Ia9e24bce79c91762c560fa3de6260716939f0b1b
Signed-off-by: Ji-yunX Lu <ji-yunx.lu@intel.com>
Cc: Eric Dong <eric.dong@intel.com>
Cc: Ray Ni <ray.ni@intel.com>
Cc: Laszlo Ersek <lersek@redhat.com>
Cc: Rahul Kumar <rahul1.kumar@intel.com>
---
 UefiCpuPkg/Library/MpInitLib/MpLib.c | 21 ++++-----------------
 1 file changed, 4 insertions(+), 17 deletions(-)

diff --git a/UefiCpuPkg/Library/MpInitLib/MpLib.c b/UefiCpuPkg/Library/MpInitLib/MpLib.c
index ab7a8ed663..70bc5da195 100644
--- a/UefiCpuPkg/Library/MpInitLib/MpLib.c
+++ b/UefiCpuPkg/Library/MpInitLib/MpLib.c
@@ -488,8 +488,8 @@ CollectProcessorCount (
   )
 {
   UINTN                  Index;
-  CPU_INFO_IN_HOB        *CpuInfoInHob;
   BOOLEAN                X2Apic;
+  CPUID_VERSION_INFO_ECX VersionInfoEcx;
 
   //
   // Send 1st broadcast IPI to APs to wakeup APs
@@ -505,26 +505,13 @@ CollectProcessorCount (
     CpuPause ();
   }
 
-
-  //
-  // Enable x2APIC mode if
-  //  1. Number of CPU is greater than 255; or
-  //  2. There are any logical processors reporting an Initial APIC ID of 255 or greater.
-  //
   X2Apic = FALSE;
-  if (CpuMpData->CpuCount > 255) {
+  AsmCpuid (CPUID_VERSION_INFO, NULL, NULL, &VersionInfoEcx.Uint32, NULL);
+  if (VersionInfoEcx.Bits.x2APIC == 1) {
     //
-    // If there are more than 255 processor found, force to enable X2APIC
+    // Enable x2APIC mode if capable
     //
     X2Apic = TRUE;
-  } else {
-    CpuInfoInHob = (CPU_INFO_IN_HOB *) (UINTN) CpuMpData->CpuInfoInHob;
-    for (Index = 0; Index < CpuMpData->CpuCount; Index++) {
-      if (CpuInfoInHob[Index].InitialApicId >= 0xFF) {
-        X2Apic = TRUE;
-        break;
-      }
-    }
   }
 
   if (X2Apic) {
-- 
2.26.2.windows.1