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[172.10.233.147]) by smtp.gmail.com with ESMTPSA id g21sm18668943qts.18.2020.08.02.12.12.54 (version=TLS1 cipher=ECDHE-ECDSA-AES128-SHA bits=128/128); Sun, 02 Aug 2020 12:12:55 -0700 (PDT) Date: Sun, 2 Aug 2020 12:12:42 -0700 (PDT) From: Hugh Dickins X-X-Sender: hugh@eggly.anvils To: Andrew Morton cc: "Kirill A. Shutemov" , Andrea Arcangeli , Song Liu , linux-kernel@vger.kernel.org, linux-mm@kvack.org Subject: [PATCH] khugepaged: collapse_pte_mapped_thp() flush the right range Message-ID: User-Agent: Alpine 2.11 (LSU 23 2013-08-11) MIME-Version: 1.0 Content-Type: TEXT/PLAIN; charset=US-ASCII Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 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 Cc: stable@vger.kernel.org # v5.4+ --- mm/khugepaged.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) --- 5.8-rc7/mm/khugepaged.c 2020-07-26 16:58:02.189038680 -0700 +++ linux/mm/khugepaged.c 2020-08-02 10:48:59.890925896 -0700 @@ -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));