From c32f4994552ea5835cf00ce06f2f7d88c71249e5 Mon Sep 17 00:00:00 2001
From: Gerd Hoffmann <kraxel@redhat.com>
Date: Tue, 28 Feb 2023 15:47:00 +0100
Subject: [PATCH] UefiCpuPkg/MpInitLib: fix apic mode for cpu hotplug

RH-Author: Miroslav Rezanina <mrezanin@redhat.com>
RH-MergeRequest: 29: UefiCpuPkg/MpInitLib: fix apic mode for cpu hotplug
RH-Bugzilla: 2150267
RH-Acked-by: Oliver Steffen <osteffen@redhat.com>
RH-Acked-by: Jon Maloy <jmaloy@redhat.com>
RH-Commit: [1/1] e7e332ac0e6edf207b1b9692f2e1aed4a1fe7c0c

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 b9a06747ed..177d15ab5b 100644
--- a/UefiCpuPkg/Library/MpInitLib/MpLib.c
+++ b/UefiCpuPkg/Library/MpInitLib/MpLib.c
@@ -495,7 +495,9 @@ 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) {
@@ -503,6 +505,10 @@ 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++) {
-- 
2.37.3