From 2375a653fe3cd0ed5ce51672ff07a41ef4a4862d Mon Sep 17 00:00:00 2001
From: Aiken Harris <harraiken@noreply.codingworkshop.git>
Date: Mon, 11 Aug 2025 20:59:00 +0200
Subject: [PATCH] Resolve potential PDE conflict in non-PAE boot path

---
 xtldr/modules/xtos_o/i686/memory.c | 11 ++++++++++-
 1 file changed, 10 insertions(+), 1 deletion(-)

diff --git a/xtldr/modules/xtos_o/i686/memory.c b/xtldr/modules/xtos_o/i686/memory.c
index c001cfc..50f4194 100644
--- a/xtldr/modules/xtos_o/i686/memory.c
+++ b/xtldr/modules/xtos_o/i686/memory.c
@@ -88,8 +88,17 @@ XtpMapHardwareMemoryPool(IN PXTBL_PAGE_MAPPING PageMap)
     }
     else
     {
-        /* Make PDE valid (PAE disabled) */
+        /* Get PDE base address (PAE disabled) */
         LegacyPdeBase = (PHARDWARE_LEGACY_PTE)PageMap->PtePointer;
+
+        /* Check for a conflicting PDE */
+        if(LegacyPdeBase[MM_HARDWARE_VA_START >> MM_PDI_LEGACY_SHIFT].Valid)
+        {
+            /* PDE already exists and is valid, nothing to do */
+            return STATUS_EFI_SUCCESS;
+        }
+
+        /* Make PDE valid  */
         RtlZeroMemory(&LegacyPdeBase[MM_HARDWARE_VA_START >> MM_PDI_LEGACY_SHIFT], sizeof(HARDWARE_LEGACY_PTE));
         LegacyPdeBase[MM_HARDWARE_VA_START >> MM_PDI_LEGACY_SHIFT].Valid = 1;
         LegacyPdeBase[MM_HARDWARE_VA_START >> MM_PDI_LEGACY_SHIFT].PageFrameNumber = Address >> MM_PAGE_SHIFT;