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 4C1D1C77B7A for ; Fri, 19 May 2023 09:03:00 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S230333AbjESJC6 (ORCPT ); Fri, 19 May 2023 05:02:58 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:48684 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229912AbjESJCy (ORCPT ); Fri, 19 May 2023 05:02:54 -0400 Received: from foss.arm.com (foss.arm.com [217.140.110.172]) by lindbergh.monkeyblade.net (Postfix) with ESMTP id 48EFEFB for ; Fri, 19 May 2023 02:02:52 -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 552991FB; Fri, 19 May 2023 02:03:36 -0700 (PDT) Received: from [10.57.73.191] (unknown [10.57.73.191]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id D578A3F73F; Fri, 19 May 2023 02:02:49 -0700 (PDT) Message-ID: <88c125fd-2294-4650-65b1-6be56589120e@arm.com> Date: Fri, 19 May 2023 10:02:48 +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: Yu Zhao Cc: Andrew Morton , SeongJae Park , 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: <20230518110727.2106156-1-ryan.roberts@arm.com> <20230518110727.2106156-3-ryan.roberts@arm.com> From: Ryan Roberts In-Reply-To: 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 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? Thanks, Ryan