[PATCH 1/1] UefiCpuPkg/MpInitLib: fix apic mode for cpu hotplug

["Gerd Hoffmann" <kraxel@redhat.com>]

In case the number of CPUs can in increase beyond 255
due to CPU hotplug choose x2apic mode.

Signed-off-by: Gerd Hoffmann <kraxel@redhat.com>
---
 UefiCpuPkg/Library/MpInitLib/MpLib.c | 8 +++++++-
 1 file changed, 7 insertions(+), 1 deletion(-)

diff --git a/UefiCpuPkg/Library/MpInitLib/MpLib.c b/UefiCpuPkg/Library/MpInitLib/MpLib.c
index e5dc852ed95f..d73b95001263 100644
--- a/UefiCpuPkg/Library/MpInitLib/MpLib.c
+++ b/UefiCpuPkg/Library/MpInitLib/MpLib.c
@@ -526,7 +526,9 @@ CollectProcessorCount (
   //
   // 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.
+  //  2. The platform exposed the exact *boot* CPU count to us in advance, and
+  //     more than 255 logical processors are possible later, with hotplug; or
+  //  3. There are any logical processors reporting an Initial APIC ID of 255 or greater.
   //
   X2Apic = FALSE;
   if (CpuMpData->CpuCount > 255) {
@@ -534,6 +536,10 @@ CollectProcessorCount (
     // If there are more than 255 processor found, force to enable X2APIC
     //
     X2Apic = TRUE;
+  } else if ((PcdGet32 (PcdCpuBootLogicalProcessorNumber) > 0) &&
+             (PcdGet32 (PcdCpuMaxLogicalProcessorNumber) > 255))
+  {
+    X2Apic = TRUE;
   } else {
     CpuInfoInHob = (CPU_INFO_IN_HOB *)(UINTN)CpuMpData->CpuInfoInHob;
     for (Index = 0; Index < CpuMpData->CpuCount; Index++) {
-- 
2.39.2