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 Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id CFD98C77B73 for ; Mon, 22 May 2023 08:54:30 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S232482AbjEVIy3 (ORCPT ); Mon, 22 May 2023 04:54:29 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:40412 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S232621AbjEVIyG (ORCPT ); Mon, 22 May 2023 04:54:06 -0400 Received: from foss.arm.com (foss.arm.com [217.140.110.172]) by lindbergh.monkeyblade.net (Postfix) with ESMTP id CCAE2138 for ; Mon, 22 May 2023 01:54:00 -0700 (PDT) Received: from usa-sjc-imap-foss1.foss.arm.com (unknown [10.121.207.14]) by usa-sjc-mx-foss1.foss.arm.com (Postfix) with ESMTP id 6FDDC11FB; Mon, 22 May 2023 01:54:45 -0700 (PDT) Received: from [10.57.73.5] (unknown [10.57.73.5]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id 62E3C3F6C4; Mon, 22 May 2023 01:53:58 -0700 (PDT) Message-ID: <1a6468c3-0395-173d-7a0a-96dcd4f7616c@arm.com> Date: Mon, 22 May 2023 09:53:56 +0100 MIME-Version: 1.0 User-Agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10.15; rv:102.0) Gecko/20100101 Thunderbird/102.11.0 Subject: Re: [PATCH v2 2/5] mm: damon must atomically clear young on ptes and pmds To: SeongJae Park Cc: Yu Zhao , Andrew Morton , Christoph Hellwig , "Matthew Wilcox (Oracle)" , "Kirill A. Shutemov" , Lorenzo Stoakes , Uladzislau Rezki , Zi Yan , linux-kernel@vger.kernel.org, linux-mm@kvack.org, damon@lists.linux.dev References: <20230519195435.90394-1-sj@kernel.org> From: Ryan Roberts In-Reply-To: <20230519195435.90394-1-sj@kernel.org> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 19/05/2023 20:54, SeongJae Park wrote: > On Fri, 19 May 2023 10:02:48 +0100 Ryan Roberts wrote: > >> On 19/05/2023 00:19, Yu Zhao wrote: >>> On Thu, May 18, 2023 at 5:07 AM Ryan Roberts wrote: >>>> >>>> It is racy to non-atomically read a pte, then clear the young bit, then >>>> write it back as this could discard dirty information. Further, it is >>>> bad practice to directly set a pte entry within a table. Instead >>>> clearing young must go through the arch-provided helper, >>>> ptep_test_and_clear_young() to ensure it is modified atomically and to >>>> give the arch code visibility and allow it to check (and potentially >>>> modify) the operation. >>>> >>>> Fixes: 46c3a0accdc4 ("mm/damon/vaddr: separate commonly usable functions") >>> >>> This should be a separate patch, since it's independent from what the >>> series tries to do. >>> >>> And that patch should cc stable, since it fixes user data corruption. >> >> Fair point. The first 3 patches are fixes for issues I found during the >> conversion. So if you're ok with it, I'll split into 2 series; the first 3 >> patches in the first, and the conversion to ptep_deref() (or ptep_get(), as per >> your comments in the other thread) in the second. I guess the whole first series >> should go to stable. >> >> Let me know if you disagree. >> >>> >>>> Signed-off-by: Ryan Roberts >>>> Reviewed-by: Zi Yan >>>> --- >>>> mm/damon/ops-common.c | 16 ++++++---------- >>>> mm/damon/ops-common.h | 4 ++-- >>>> mm/damon/paddr.c | 4 ++-- >>>> mm/damon/vaddr.c | 4 ++-- >>>> 4 files changed, 12 insertions(+), 16 deletions(-) >>>> >>>> diff --git a/mm/damon/ops-common.c b/mm/damon/ops-common.c >>>> index cc63cf953636..acc264b97903 100644 >>>> --- a/mm/damon/ops-common.c >>>> +++ b/mm/damon/ops-common.c >>>> @@ -37,7 +37,7 @@ struct folio *damon_get_folio(unsigned long pfn) >>>> return folio; >>>> } >>>> >>>> -void damon_ptep_mkold(pte_t *pte, struct mm_struct *mm, unsigned long addr) >>>> +void damon_ptep_mkold(pte_t *pte, struct vm_area_struct *vma, unsigned long addr) >>>> { >>>> bool referenced = false; >>>> struct folio *folio = damon_get_folio(pte_pfn(*pte)); >>>> @@ -45,13 +45,11 @@ void damon_ptep_mkold(pte_t *pte, struct mm_struct *mm, unsigned long addr) >>>> if (!folio) >>>> return; >>>> >>>> - if (pte_young(*pte)) { >>>> + if (ptep_test_and_clear_young(vma, addr, pte)) >>>> referenced = true; >>>> - *pte = pte_mkold(*pte); >>>> - } >>>> >>>> #ifdef CONFIG_MMU_NOTIFIER >>>> - if (mmu_notifier_clear_young(mm, addr, addr + PAGE_SIZE)) >>>> + if (mmu_notifier_clear_young(vma->vm_mm, addr, addr + PAGE_SIZE)) >>>> referenced = true; >>>> #endif /* CONFIG_MMU_NOTIFIER */ >>> >>> Use ptep_clear_young_notify(). Similar below. >> >> This looks sensible but I'd like clarification from SeongJae: Are you happy for >> me to do this refactoring as part of the patch? > > Yes, I would be happy for that :) Nevertheless, because that's a refactoring > rather than a fix, I'd be happier if you could do that with a separate patch. Great - I'll do it like this for v3. > > > Thanks, > SJ > >> >> Thanks, >> Ryan >>