From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752191AbdLDQok (ORCPT ); Mon, 4 Dec 2017 11:44:40 -0500 Received: from mail.linuxfoundation.org ([140.211.169.12]:60420 "EHLO mail.linuxfoundation.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752258AbdLDP7l (ORCPT ); Mon, 4 Dec 2017 10:59:41 -0500 From: Greg Kroah-Hartman To: linux-kernel@vger.kernel.org Cc: Greg Kroah-Hartman , stable@vger.kernel.org, "Kirill A. Shutemov" , Michal Hocko , Hugh Dickins , Linus Torvalds , Ben Hutchings Subject: [PATCH 3.18 03/12] mm, thp: Do not make page table dirty unconditionally in touch_p[mu]d() Date: Mon, 4 Dec 2017 16:59:17 +0100 Message-Id: <20171204155916.616760251@linuxfoundation.org> X-Mailer: git-send-email 2.15.1 In-Reply-To: <20171204155916.489136969@linuxfoundation.org> References: <20171204155916.489136969@linuxfoundation.org> User-Agent: quilt/0.65 MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 3.18-stable review patch. If anyone has any objections, please let me know. ------------------ From: Kirill A. Shutemov commit a8f97366452ed491d13cf1e44241bc0b5740b1f0 upstream. Currently, we unconditionally make page table dirty in touch_pmd(). It may result in false-positive can_follow_write_pmd(). We may avoid the situation, if we would only make the page table entry dirty if caller asks for write access -- FOLL_WRITE. The patch also changes touch_pud() in the same way. Signed-off-by: Kirill A. Shutemov Cc: Michal Hocko Cc: Hugh Dickins Signed-off-by: Linus Torvalds [Salvatore Bonaccorso: backport for 3.16: - Adjust context - Drop specific part for PUD-sized transparent hugepages. Support for PUD-sized transparent hugepages was added in v4.11-rc1 ] Signed-off-by: Ben Hutchings Signed-off-by: Greg Kroah-Hartman --- mm/huge_memory.c | 14 ++++---------- 1 file changed, 4 insertions(+), 10 deletions(-) --- a/mm/huge_memory.c +++ b/mm/huge_memory.c @@ -1240,17 +1240,11 @@ struct page *follow_trans_huge_pmd(struc VM_BUG_ON_PAGE(!PageHead(page), page); if (flags & FOLL_TOUCH) { pmd_t _pmd; - /* - * We should set the dirty bit only for FOLL_WRITE but - * for now the dirty bit in the pmd is meaningless. - * And if the dirty bit will become meaningful and - * we'll only set it with FOLL_WRITE, an atomic - * set_bit will be required on the pmd to set the - * young bit, instead of the current set_pmd_at. - */ - _pmd = pmd_mkyoung(pmd_mkdirty(*pmd)); + _pmd = pmd_mkyoung(*pmd); + if (flags & FOLL_WRITE) + _pmd = pmd_mkdirty(_pmd); if (pmdp_set_access_flags(vma, addr & HPAGE_PMD_MASK, - pmd, _pmd, 1)) + pmd, _pmd, flags & FOLL_WRITE)) update_mmu_cache_pmd(vma, addr, pmd); } if ((flags & FOLL_MLOCK) && (vma->vm_flags & VM_LOCKED)) {