[PATCH 2/2] OvmfPkg: Fix PciHostBridgeLibScan

["Sean Rhodes" <sean@starlabs.systems>]

From: Patrick Rudolph <patrick.rudolph@9elements.com>

Don't assume a 64bit register always holds an address greater than 4GB.
Check the value in the register and decide which Aperature it should be
assigned to.

The same code caused an issue on real hardware. It's unclear if this is an
issue here as well, as it's intended to run on emulated hardware only.

Cc: Ard Biesheuvel <ardb+tianocore@kernel.org>
Cc: Jiewen Yao <jiewen.yao@intel.com>
Cc: Jordan Justen <jordan.l.justen@intel.com>
Cc: Gerd Hoffmann <kraxel@redhat.com>
Signed-off-by: Patrick Rudolph <patrick.rudolph@9elements.com>
---
 .../PciHostBridgeLibScan/ScanForRootBridges.c        | 12 ++++++++----
 1 file changed, 8 insertions(+), 4 deletions(-)

diff --git a/OvmfPkg/Library/PciHostBridgeLibScan/ScanForRootBridges.c b/OvmfPkg/Library/PciHostBridgeLibScan/ScanForRootBridges.c
index 5fb02a89b9..1ff96be57f 100644
--- a/OvmfPkg/Library/PciHostBridgeLibScan/ScanForRootBridges.c
+++ b/OvmfPkg/Library/PciHostBridgeLibScan/ScanForRootBridges.c
@@ -331,14 +331,18 @@ ScanForRootBridges (
           Base  = ((UINT32)Pci.Bridge.PrefetchableMemoryBase & 0xfff0) << 16;
           Limit = (((UINT32)Pci.Bridge.PrefetchableMemoryLimit & 0xfff0)
                    << 16) | 0xfffff;
-          MemAperture = &Mem;
           if (Value == BIT0) {
-            Base       |= LShiftU64 (Pci.Bridge.PrefetchableBaseUpper32, 32);
-            Limit      |= LShiftU64 (Pci.Bridge.PrefetchableLimitUpper32, 32);
-            MemAperture = &MemAbove4G;
+            Base  |= LShiftU64 (Pci.Bridge.PrefetchableBaseUpper32, 32);
+            Limit |= LShiftU64 (Pci.Bridge.PrefetchableLimitUpper32, 32);
           }
 
           if (Base < Limit) {
+            if (Base < BASE_4GB) {
+              MemAperture = &Mem;
+            } else {
+              MemAperture = &MemAbove4G;
+            }
+
             if (MemAperture->Base > Base) {
               MemAperture->Base = Base;
             }
-- 
2.32.0