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 kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by smtp.lore.kernel.org (Postfix) with ESMTP id D9A23C00140 for ; Thu, 18 Aug 2022 05:07:10 +0000 (UTC) Received: by kanga.kvack.org (Postfix) id 394D18D0001; Thu, 18 Aug 2022 01:07:10 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id 31D396B0074; Thu, 18 Aug 2022 01:07:10 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 1BDA48D0001; Thu, 18 Aug 2022 01:07:10 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from relay.hostedemail.com (smtprelay0015.hostedemail.com [216.40.44.15]) by kanga.kvack.org (Postfix) with ESMTP id 07EEE6B0073 for ; Thu, 18 Aug 2022 01:07:10 -0400 (EDT) Received: from smtpin28.hostedemail.com (a10.router.float.18 [10.200.18.1]) by unirelay10.hostedemail.com (Postfix) with ESMTP id CB330C09E7 for ; Thu, 18 Aug 2022 05:07:09 +0000 (UTC) X-FDA: 79811529378.28.B8806F3 Received: from out30-133.freemail.mail.aliyun.com (out30-133.freemail.mail.aliyun.com [115.124.30.133]) by imf11.hostedemail.com (Postfix) with ESMTP id A755E4009B for ; Thu, 18 Aug 2022 05:07:07 +0000 (UTC) X-Alimail-AntiSpam:AC=PASS;BC=-1|-1;BR=01201311R171e4;CH=green;DM=||false|;DS=||;FP=0|-1|-1|-1|0|-1|-1|-1;HT=ay29a033018045192;MF=baolin.wang@linux.alibaba.com;NM=1;PH=DS;RN=7;SR=0;TI=SMTPD_---0VMZPdun_1660799221; Received: from 30.97.48.48(mailfrom:baolin.wang@linux.alibaba.com fp:SMTPD_---0VMZPdun_1660799221) by smtp.aliyun-inc.com; Thu, 18 Aug 2022 13:07:02 +0800 Message-ID: Date: Thu, 18 Aug 2022 13:07:13 +0800 MIME-Version: 1.0 User-Agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:91.0) Gecko/20100101 Thunderbird/91.12.0 Subject: Re: [PATCH] mm/damon: Validate if the pmd entry is present before accessing To: Muchun Song Cc: sj@kernel.org, Andrew Morton , damon@lists.linux.dev, Linux MM , linux-kernel@vger.kernel.org, Mike Kravetz References: <2838b6737bc259cf575ff11fd1c4b7fdb340fa73.1660717122.git.baolin.wang@linux.alibaba.com> <5173E308-2403-4667-9162-865CF7F11838@linux.dev> <6F99AE03-3C74-4E5B-87E1-6F3232BEEBB5@linux.dev> From: Baolin Wang In-Reply-To: <6F99AE03-3C74-4E5B-87E1-6F3232BEEBB5@linux.dev> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=hostedemail.com; s=arc-20220608; t=1660799228; h=from:from:sender:reply-to:subject:subject:date:date: message-id:message-id:to:to:cc:cc:mime-version:mime-version: content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=cFr6K8Wt2QaN4iXnd6+b87leN+2hSHvftAGsonVRisw=; b=q3dwQwMBVdxkR68JkoT13uK1OLlrHmTL8I1owcKHfyfIrGugU6QD2yrs9qvKFBLfQEP5Lh NqDcGsvUzQYBhIYwXvSHKTZcCvXw6VVnmCLannUCdcFYTPoTJSwZ9oQmGIyelOoPjSWd6b EUNx2HoQ28OqDWWXKNZrUXcsfPiMHYk= ARC-Authentication-Results: i=1; imf11.hostedemail.com; dkim=none; dmarc=pass (policy=none) header.from=alibaba.com; spf=pass (imf11.hostedemail.com: domain of baolin.wang@linux.alibaba.com designates 115.124.30.133 as permitted sender) smtp.mailfrom=baolin.wang@linux.alibaba.com ARC-Seal: i=1; s=arc-20220608; d=hostedemail.com; t=1660799228; a=rsa-sha256; cv=none; b=Hoa9W85Gl9HEx1OseqV/qGLBC6R+FqnrRTqm+saHgsWdLOkGEZyf46TE2XvEcSRmUJ71FR U/sD2cM7HGgp1b1E0/r+s8kt7o6IuzLcT+iQiN2EEU63qMnpqtZd3oDxzrpzsJKwdqnxtz UDhGNaHdlWViQLnm3bzkteAfSJ7BCxQ= Authentication-Results: imf11.hostedemail.com; dkim=none; dmarc=pass (policy=none) header.from=alibaba.com; spf=pass (imf11.hostedemail.com: domain of baolin.wang@linux.alibaba.com designates 115.124.30.133 as permitted sender) smtp.mailfrom=baolin.wang@linux.alibaba.com X-Stat-Signature: pr66xzxa4e3s1y7k6mpsp4fsf9o7mnzf X-Rspamd-Queue-Id: A755E4009B X-Rspam-User: X-Rspamd-Server: rspam01 X-HE-Tag: 1660799227-814232 X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: On 8/18/2022 11:39 AM, Muchun Song wrote: > > >> On Aug 18, 2022, at 10:57, Baolin Wang wrote: >> >> >> >> 在 8/18/2022 10:41 AM, Muchun Song 写道: >>>> On Aug 17, 2022, at 14:21, Baolin Wang wrote: >>>> >>>> The pmd_huge() is used to validate if the pmd entry is mapped by a huge >>>> page, also including the case of non-present (migration or hwpoisoned) >>>> pmd entry on arm64 or x86 architectures. Thus we should validate if it >>>> is present before making the pmd entry old or getting young state, >>>> otherwise we can not get the correct corresponding page. >>>> >>>> Signed-off-by: Baolin Wang >>>> --- >>>> mm/damon/vaddr.c | 10 ++++++++++ >>>> 1 file changed, 10 insertions(+) >>>> >>>> diff --git a/mm/damon/vaddr.c b/mm/damon/vaddr.c >>>> index 3c7b9d6..1d16c6c 100644 >>>> --- a/mm/damon/vaddr.c >>>> +++ b/mm/damon/vaddr.c >>>> @@ -304,6 +304,11 @@ static int damon_mkold_pmd_entry(pmd_t *pmd, unsigned long addr, >>>> >>>> if (pmd_huge(*pmd)) { >>>> ptl = pmd_lock(walk->mm, pmd); >>>> + if (!pmd_present(*pmd)) { >>> Unluckily, we should use pte_present here. See commit c9d398fa23788. We can use >>> huge_ptep_get() to get a hugetlb pte, so it’s better to put the check after >>> pmd_huge. >> >> IMO this is not the case for hugetlb, and the hugetlb case will be handled by damon_mkold_hugetlb_entry(), which already used pte_present() for hugetlb case. > > Well, I thought it is hugetlb related since I saw the usage of pmd_huge. If it is THP case, why > not use pmd_trans_huge? IIUC, it can not guarantee the pmd is present if pmd_trans_huge() returns true on all architectures, at least on X86, we still need pmd_present() validation. So changing to pmd_trans_huge() does not make code simpler from my side, and I prefer to keep this patch. Maybe we can send another cleanup patch to replace pmd_huge() with pmd_trans_huge() for THP case to make code more readable? How do you think? Thanks. >> >>> Cc Mike to make sure I am not missing something. >>> Muchun, >>> Thanks. >>>> + spin_unlock(ptl); >>>> + return 0; >>>> + } >>>> + >>>> if (pmd_huge(*pmd)) { >>>> damon_pmdp_mkold(pmd, walk->mm, addr); >>>> spin_unlock(ptl); >>>> @@ -431,6 +436,11 @@ static int damon_young_pmd_entry(pmd_t *pmd, unsigned long addr, >>>> #ifdef CONFIG_TRANSPARENT_HUGEPAGE >>>> if (pmd_huge(*pmd)) { >>>> ptl = pmd_lock(walk->mm, pmd); >>>> + if (!pmd_present(*pmd)) { >>>> + spin_unlock(ptl); >>>> + return 0; >>>> + } >>>> + >>>> if (!pmd_huge(*pmd)) { >>>> spin_unlock(ptl); >>>> goto regular_page; >>>> -- >>>> 1.8.3.1