[reactos] 89/100: [NTOS:MM] Keep a ref on the segment when mapping a page & keep trace of what is the highest offset mapped.

[Jérôme Gardou]

https://git.reactos.org/?p=reactos.git;a=commitdiff;h=c1c51e31e439240fec454…

commit c1c51e31e439240fec4542b002dae925ccfb9e3b
Author:     Jérôme Gardou <jerome.gardou(a)reactos.org>
AuthorDate: Wed Jan 27 16:59:37 2021 +0100
Commit:     Jérôme Gardou <jerome.gardou(a)reactos.org>
CommitDate: Wed Feb 3 09:41:23 2021 +0100

    [NTOS:MM] Keep a ref on the segment when mapping a page & keep trace of what is
the highest offset mapped.
---
 ntoskrnl/cache/section/sptab.c | 23 ++++++++++++++++++++++-
 ntoskrnl/mm/section.c          |  3 ---
 2 files changed, 22 insertions(+), 4 deletions(-)

diff --git a/ntoskrnl/cache/section/sptab.c b/ntoskrnl/cache/section/sptab.c
index f0cb3d36c2a..7d960a1ff08 100644
--- a/ntoskrnl/cache/section/sptab.c
+++ b/ntoskrnl/cache/section/sptab.c
@@ -218,14 +218,35 @@ _MmSetPageEntrySectionSegment(PMM_SECTION_SEGMENT Segment,
         }
         else
         {
-            /* We're switching to a valid entry from an invalid one. Add the Rmap */
+            /*
+             * We're switching to a valid entry from an invalid one.
+             * Add the Rmap and take a ref on the segment.
+             */
             MmSetSectionAssociation(PFN_FROM_SSE(Entry), Segment, Offset);
+            InterlockedIncrement64(Segment->ReferenceCount);
+
+            if ((Offset->QuadPart > (Segment->LastPage << PAGE_SHIFT)) ||
!Segment->LastPage)
+                Segment->LastPage = (Offset->QuadPart >> PAGE_SHIFT) + 1;
         }
     }
     else if (OldEntry && !IS_SWAP_FROM_SSE(OldEntry))
     {
         /* We're switching to an invalid entry from a valid one */
         MmDeleteSectionAssociation(PFN_FROM_SSE(OldEntry));
+        MmDereferenceSegment(Segment);
+
+        if (Offset->QuadPart == ((Segment->LastPage - 1ULL) << PAGE_SHIFT))
+        {
+            /* We are unsetting the last page */
+            while (--Segment->LastPage)
+            {
+                LARGE_INTEGER CheckOffset;
+                CheckOffset.QuadPart = (Segment->LastPage - 1) << PAGE_SHIFT;
+                ULONG_PTR Entry = MmGetPageEntrySectionSegment(Segment,
&CheckOffset);
+                if ((Entry != 0) && !IS_SWAP_FROM_SSE(Entry))
+                    break;
+            }
+        }
     }
 
     PageTable->PageEntries[PageIndex] = Entry;
diff --git a/ntoskrnl/mm/section.c b/ntoskrnl/mm/section.c
index 16767458bce..8515820e116 100644
--- a/ntoskrnl/mm/section.c
+++ b/ntoskrnl/mm/section.c
@@ -4113,9 +4113,6 @@ MmCanFileBeTruncated (IN PSECTION_OBJECT_POINTERS
SectionObjectPointer,
     return Ret;
 }
 
-
-
-
 /*
  * @implemented
  */