From 0395049986556503da00c20dbfe69dc531984956 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?J=C3=A9r=C3=B4me=20Gardou?= <jerome.gardou@reactos.org>
Date: Fri, 21 May 2021 10:49:53 +0200
Subject: [PATCH] [NTOS:KE] Do not call MmSetPageProtect for the Pentium Lock
 Errata

CORE-17589
---
 ntoskrnl/ke/i386/cpu.c | 6 +++++-
 1 file changed, 5 insertions(+), 1 deletion(-)

diff --git a/ntoskrnl/ke/i386/cpu.c b/ntoskrnl/ke/i386/cpu.c
index 3b07453af53..bdc92f908fd 100644
--- a/ntoskrnl/ke/i386/cpu.c
+++ b/ntoskrnl/ke/i386/cpu.c
@@ -1089,6 +1089,7 @@ KiI386PentiumLockErrataFixup(VOID)
 {
     KDESCRIPTOR IdtDescriptor = {0, 0, 0};
     PKIDTENTRY NewIdt, NewIdt2;
+    PMMPTE PointerPte;
 
     /* Allocate memory for a new IDT */
     NewIdt = ExAllocatePool(NonPagedPool, 2 * PAGE_SIZE);
@@ -1114,7 +1115,10 @@ KiI386PentiumLockErrataFixup(VOID)
     _enable();
 
     /* Set the first 7 entries as read-only to produce a fault */
-    MmSetPageProtect(NULL, NewIdt, PAGE_READONLY);
+    PointerPte = MiAddressToPte(NewIdt);
+    ASSERT(PointerPte->u.Hard.Write == 1);
+    PointerPte->u.Hard.Write = 0;
+    KeInvalidateTlbEntry(NewIdt);
 }
 
 BOOLEAN