From 80dd9f5a90487188213da24ff1e46335461e2281 Mon Sep 17 00:00:00 2001
From: Timo Kreuzer <timo.kreuzer@reactos.org>
Date: Mon, 10 Apr 2023 22:14:23 +0300
Subject: [PATCH] [NTOS:Mm] Add PFN ShareCount handling to old Mm

---
 ntoskrnl/mm/i386/page.c | 22 ++++++++++++++++++++--
 1 file changed, 20 insertions(+), 2 deletions(-)

diff --git a/ntoskrnl/mm/i386/page.c b/ntoskrnl/mm/i386/page.c
index 4c64dd2a941..38cd5066256 100644
--- a/ntoskrnl/mm/i386/page.c
+++ b/ntoskrnl/mm/i386/page.c
@@ -325,7 +325,18 @@ MmDeleteVirtualMappingEx(
 
         if (!IsPhysical && OldPte.u.Hard.Valid)
         {
-            // TODO: Handle PFN ShareCount
+            PMMPFN Pfn1;
+            KIRQL OldIrql;
+
+            OldIrql = MiAcquirePfnLock();
+            Pfn1 = &MmPfnDatabase[OldPte.u.Hard.PageFrameNumber];
+            ASSERT(Pfn1->u3.e1.PageLocation == ActiveAndValid);
+            ASSERT(Pfn1->u2.ShareCount > 0);
+            if (--Pfn1->u2.ShareCount == 0)
+            {
+                Pfn1->u3.e1.PageLocation = TransitionPage;
+            }
+            MiReleasePfnLock(OldIrql);
         }
 
         MiUnlockProcessWorkingSetUnsafe(Process, PsGetCurrentThread());
@@ -685,7 +696,14 @@ MmCreateVirtualMappingUnsafeEx(
 
     if (!IsPhysical)
     {
-        // TODO: Handle PFN ShareCount
+        PMMPFN Pfn1;
+        KIRQL OldIrql;
+
+        OldIrql = MiAcquirePfnLock();
+        Pfn1 = &MmPfnDatabase[TempPte.u.Hard.PageFrameNumber];
+        Pfn1->u2.ShareCount++;
+        Pfn1->u3.e1.PageLocation = ActiveAndValid;
+        MiReleasePfnLock(OldIrql);
     }
 
     /* We don't need to flush the TLB here because it only caches valid translations