From c28306c3d6e0c7721abc937d8f47c3f1ccecf323 Mon Sep 17 00:00:00 2001
From: "Ma, Maurice" <maurice.ma@intel.com>
Date: Tue, 17 May 2016 05:26:06 +0800
Subject: MdeModulePkg: Skip invalid bus number scanning in PciBusDxe driver

When PcdPciDisableBusEnumeration is enabled, the PciBus driver
might get into a dead loop if the secondary bus register on PCI
bridge is not programmed or programmed improperly. Adding this
check to avoid any potential dead loop caused by this.

Cc: Feng Tian <feng.tian@intel.com>
Cc: Star Zeng <star.zeng@intel.com>
Contributed-under: TianoCore Contribution Agreement 1.0
Signed-off-by: Maurice Ma <maurice.ma@intel.com>
Reviewed-by: Ruiyu Ni <ruiyu.ni@intel.com>
Reviewed-by: Lee Leahy <Leroy.p.leahy@intel.com>
---
 MdeModulePkg/Bus/Pci/PciBusDxe/PciEnumeratorSupport.c | 8 ++++++++
 1 file changed, 8 insertions(+)

diff --git a/MdeModulePkg/Bus/Pci/PciBusDxe/PciEnumeratorSupport.c b/MdeModulePkg/Bus/Pci/PciBusDxe/PciEnumeratorSupport.c
index a6ade26e3a..086c481130 100644
--- a/MdeModulePkg/Bus/Pci/PciBusDxe/PciEnumeratorSupport.c
+++ b/MdeModulePkg/Bus/Pci/PciBusDxe/PciEnumeratorSupport.c
@@ -164,6 +164,14 @@ PciPciDeviceInfoCollector (
             return Status;
           }
 
+          //
+          // Ensure secondary bus number is greater than the primary bus number to avoid
+          // any potential dead loop when PcdPciDisableBusEnumeration is set to TRUE
+          //
+          if (SecBus <= StartBusNumber) {
+            break;
+          }
+
           //
           // Get resource padding for PPB
           //
-- 
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