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From:   Greg Kroah-Hartman <gregkh@linuxfoundation.org>
To:     linux-kernel@vger.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        stable@vger.kernel.org, Hugh Dickins <hughd@google.com>,
        Andrew Morton <akpm@linux-foundation.org>,
        "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>,
        Andrea Arcangeli <aarcange@redhat.com>,
        Mike Kravetz <mike.kravetz@oracle.com>,
        Song Liu <songliubraving@fb.com>,
        Linus Torvalds <torvalds@linux-foundation.org>
Subject: [PATCH 5.8 077/232] khugepaged: collapse_pte_mapped_thp() flush the right range
Date:   Thu, 20 Aug 2020 11:18:48 +0200
Message-Id: <20200820091616.540850550@linuxfoundation.org>
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From: Hugh Dickins <hughd@google.com>

commit 723a80dafed5c95889d48baab9aa433a6ffa0b4e upstream.

pmdp_collapse_flush() should be given the start address at which the huge
page is mapped, haddr: it was given addr, which at that point has been
used as a local variable, incremented to the end address of the extent.

Found by source inspection while chasing a hugepage locking bug, which I
then could not explain by this.  At first I thought this was very bad;
then saw that all of the page translations that were not flushed would
actually still point to the right pages afterwards, so harmless; then
realized that I know nothing of how different architectures and models
cache intermediate paging structures, so maybe it matters after all -
particularly since the page table concerned is immediately freed.

Much easier to fix than to think about.

Fixes: 27e1f8273113 ("khugepaged: enable collapse pmd for pte-mapped THP")
Signed-off-by: Hugh Dickins <hughd@google.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Acked-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: Mike Kravetz <mike.kravetz@oracle.com>
Cc: Song Liu <songliubraving@fb.com>
Cc: <stable@vger.kernel.org>	[5.4+]
Link: http://lkml.kernel.org/r/alpine.LSU.2.11.2008021204390.27773@eggly.anvils
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

---
 mm/khugepaged.c |    2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

--- a/mm/khugepaged.c
+++ b/mm/khugepaged.c
@@ -1502,7 +1502,7 @@ void collapse_pte_mapped_thp(struct mm_s
 
 	/* step 4: collapse pmd */
 	ptl = pmd_lock(vma->vm_mm, pmd);
-	_pmd = pmdp_collapse_flush(vma, addr, pmd);
+	_pmd = pmdp_collapse_flush(vma, haddr, pmd);
 	spin_unlock(ptl);
 	mm_dec_nr_ptes(mm);
 	pte_free(mm, pmd_pgtable(_pmd));