From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-7.0 required=3.0 tests=DKIM_SIGNED,DKIM_VALID, DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH,MAILING_LIST_MULTI, SIGNED_OFF_BY,SPF_PASS,URIBL_BLOCKED autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id E7C65C07E85 for ; Tue, 11 Dec 2018 08:21:55 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id A039F2082F for ; Tue, 11 Dec 2018 08:21:53 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (1024-bit key) header.d=yandex-team.ru header.i=@yandex-team.ru header.b="nWr83pET"; dkim=pass (1024-bit key) header.d=yandex-team.ru header.i=@yandex-team.ru header.b="GEUl5J07" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org A039F2082F Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=yandex-team.ru Authentication-Results: mail.kernel.org; spf=none smtp.mailfrom=linux-kernel-owner@vger.kernel.org Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726179AbeLKIVw (ORCPT ); Tue, 11 Dec 2018 03:21:52 -0500 Received: from forwardcorp1j.cmail.yandex.net ([5.255.227.105]:59861 "EHLO forwardcorp1j.cmail.yandex.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726085AbeLKIVw (ORCPT ); Tue, 11 Dec 2018 03:21:52 -0500 Received: from mxbackcorp2j.mail.yandex.net (mxbackcorp2j.mail.yandex.net [IPv6:2a02:6b8:0:1619::119]) by forwardcorp1j.cmail.yandex.net (Yandex) with ESMTP id 0FD24206B4; Tue, 11 Dec 2018 11:21:47 +0300 (MSK) Received: from smtpcorp1o.mail.yandex.net (smtpcorp1o.mail.yandex.net [2a02:6b8:0:1a2d::30]) by mxbackcorp2j.mail.yandex.net (nwsmtp/Yandex) with ESMTP id BWCnWWxZ58-LkUGgOoP; Tue, 11 Dec 2018 11:21:47 +0300 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=yandex-team.ru; s=default; t=1544516507; bh=DdBL61cK/P+YLJ2wkFY4SMpy1Nlgfc3ORSx3E0oTjjE=; h=Subject:To:Cc:References:From:Message-ID:Date:In-Reply-To; b=nWr83pETY52H6OcT3yCGF+TdGLPbkdzPCZMzBKetvRXYp8tO9/2Lhz+wHmKYA/KLU YsFRsO9SG9Wl2iIDVM4LBzacBYM4FlxkSnGfav0MVfN+6yPgytlK3SGJEuB9CCEoZE 1ojXbdpPb1uK+EbQMe/20pZI7dAAgODpjsmrZywg= Received: from dynamic-iva.dhcp.yndx.net (dynamic-iva.dhcp.yndx.net [2a02:6b8:0:827::1:67]) by smtpcorp1o.mail.yandex.net (nwsmtp/Yandex) with ESMTPSA id n4TZlARbny-LkBGki4b; Tue, 11 Dec 2018 11:21:46 +0300 (using TLSv1.2 with cipher ECDHE-RSA-AES128-GCM-SHA256 (128/128 bits)) (Client certificate not present) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=yandex-team.ru; s=default; t=1544516506; bh=DdBL61cK/P+YLJ2wkFY4SMpy1Nlgfc3ORSx3E0oTjjE=; h=Subject:To:Cc:References:From:Message-ID:Date:In-Reply-To; b=GEUl5J07/Ukd3XFQOuDT57oFZIurf+P8zx+e1FmHVXzBe5FNdSwZD+l/UVtPM83UB spV1rQ3tCtHNSgQQJBC12Gq33kJ7QL/VC9XNs3t/3SDeIvsNqVbndJCuaKtSGNlbm1 US7Zd+LqnF7pF+T09XhWWV8GPsBM4iLStEXDotSY= Authentication-Results: smtpcorp1o.mail.yandex.net; dkim=pass header.i=@yandex-team.ru Subject: Re: [PATCH v2] mm: thp: fix flags for pmd migration when split To: Peter Xu , linux-kernel@vger.kernel.org Cc: Andrea Arcangeli , Andrew Morton , "Kirill A. Shutemov" , Matthew Wilcox , Michal Hocko , Dave Jiang , "Aneesh Kumar K.V" , Souptick Joarder , linux-mm@kvack.org References: <20181211051254.16633-1-peterx@redhat.com> From: Konstantin Khlebnikov Message-ID: <1fc103f7-3164-007d-bcfd-7ad7c60bb6ec@yandex-team.ru> Date: Tue, 11 Dec 2018 11:21:44 +0300 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:60.0) Gecko/20100101 Thunderbird/60.2.1 MIME-Version: 1.0 In-Reply-To: <20181211051254.16633-1-peterx@redhat.com> Content-Type: text/plain; charset=utf-8; format=flowed Content-Language: en-CA Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 11.12.2018 8:12, Peter Xu wrote: > When splitting a huge migrating PMD, we'll transfer all the existing > PMD bits and apply them again onto the small PTEs. However we are > fetching the bits unconditionally via pmd_soft_dirty(), pmd_write() > or pmd_yound() while actually they don't make sense at all when it's > a migration entry. Fix them up by make it conditional. > > Note that if my understanding is correct about the problem then if > without the patch there is chance to lose some of the dirty bits in > the migrating pmd pages (on x86_64 we're fetching bit 11 which is part > of swap offset instead of bit 2) and it could potentially corrupt the > memory of an userspace program which depends on the dirty bit. > > CC: Andrea Arcangeli > CC: Andrew Morton > CC: "Kirill A. Shutemov" > CC: Matthew Wilcox > CC: Michal Hocko > CC: Dave Jiang > CC: "Aneesh Kumar K.V" > CC: Souptick Joarder > CC: Konstantin Khlebnikov > CC: linux-mm@kvack.org > CC: linux-kernel@vger.kernel.org > Signed-off-by: Peter Xu > --- > v2: > - fix it up for young/write/dirty bits too [Konstantin] > --- > mm/huge_memory.c | 15 ++++++++++----- > 1 file changed, 10 insertions(+), 5 deletions(-) > > diff --git a/mm/huge_memory.c b/mm/huge_memory.c > index f2d19e4fe854..b00941b3d342 100644 > --- a/mm/huge_memory.c > +++ b/mm/huge_memory.c > @@ -2157,11 +2157,16 @@ static void __split_huge_pmd_locked(struct vm_area_struct *vma, pmd_t *pmd, > page = pmd_page(old_pmd); > VM_BUG_ON_PAGE(!page_count(page), page); > page_ref_add(page, HPAGE_PMD_NR - 1); > - if (pmd_dirty(old_pmd)) > - SetPageDirty(page); > - write = pmd_write(old_pmd); > - young = pmd_young(old_pmd); > - soft_dirty = pmd_soft_dirty(old_pmd); > + if (unlikely(pmd_migration)) { > + soft_dirty = pmd_swp_soft_dirty(old_pmd); > + young = write = false; > + } else { > + if (pmd_dirty(old_pmd)) > + SetPageDirty(page); > + write = pmd_write(old_pmd); > + young = pmd_young(old_pmd); > + soft_dirty = pmd_soft_dirty(old_pmd); > + } Write/read-only is encoded into migration entry. I suppose there should be something like this: --- a/mm/huge_memory.c +++ b/mm/huge_memory.c @@ -2151,16 +2151,21 @@ static void __split_huge_pmd_locked(struct vm_area_struct *vma, pmd_t *pmd, entry = pmd_to_swp_entry(old_pmd); page = pfn_to_page(swp_offset(entry)); + write = is_write_migration_entry(entry); + young = false; + soft_dirty = pmd_swp_soft_dirty(old_pmd); } else #endif + { page = pmd_page(old_pmd); + if (pmd_dirty(old_pmd)) + SetPageDirty(page); + write = pmd_write(old_pmd); + young = pmd_young(old_pmd); + soft_dirty = pmd_soft_dirty(old_pmd); + } VM_BUG_ON_PAGE(!page_count(page), page); page_ref_add(page, HPAGE_PMD_NR - 1); - if (pmd_dirty(old_pmd)) - SetPageDirty(page); - write = pmd_write(old_pmd); - young = pmd_young(old_pmd); - soft_dirty = pmd_soft_dirty(old_pmd); /* * Withdraw the table only after we mark the pmd entry invalid. > > /* > * Withdraw the table only after we mark the pmd entry invalid. >