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 B7E82C00140 for ; Thu, 18 Aug 2022 05:45:42 +0000 (UTC) Received: by kanga.kvack.org (Postfix) id 10C438D0002; Thu, 18 Aug 2022 01:45:42 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id 0E00B6B0074; Thu, 18 Aug 2022 01:45:42 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id E9E858D0002; Thu, 18 Aug 2022 01:45:41 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from relay.hostedemail.com (smtprelay0017.hostedemail.com [216.40.44.17]) by kanga.kvack.org (Postfix) with ESMTP id D87016B0073 for ; Thu, 18 Aug 2022 01:45:41 -0400 (EDT) Received: from smtpin11.hostedemail.com (a10.router.float.18 [10.200.18.1]) by unirelay08.hostedemail.com (Postfix) with ESMTP id B0A2C141537 for ; Thu, 18 Aug 2022 05:45:41 +0000 (UTC) X-FDA: 79811626482.11.997BA42 Received: from out30-57.freemail.mail.aliyun.com (out30-57.freemail.mail.aliyun.com [115.124.30.57]) by imf23.hostedemail.com (Postfix) with ESMTP id 7F68A14007A for ; Thu, 18 Aug 2022 05:45:39 +0000 (UTC) X-Alimail-AntiSpam:AC=PASS;BC=-1|-1;BR=01201311R821e4;CH=green;DM=||false|;DS=||;FP=0|-1|-1|-1|0|-1|-1|-1;HT=ay29a033018045168;MF=baolin.wang@linux.alibaba.com;NM=1;PH=DS;RN=7;SR=0;TI=SMTPD_---0VMZQY1e_1660801534; Received: from 30.97.48.48(mailfrom:baolin.wang@linux.alibaba.com fp:SMTPD_---0VMZQY1e_1660801534) by smtp.aliyun-inc.com; Thu, 18 Aug 2022 13:45:35 +0800 Message-ID: <098c1480-416d-bca9-cedb-ca495df69b64@linux.alibaba.com> Date: Thu, 18 Aug 2022 13:45:46 +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> <8C1A5089-2830-407D-8FF3-2F0F92984645@linux.dev> From: Baolin Wang In-Reply-To: <8C1A5089-2830-407D-8FF3-2F0F92984645@linux.dev> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit ARC-Authentication-Results: i=1; imf23.hostedemail.com; dkim=none; spf=pass (imf23.hostedemail.com: domain of baolin.wang@linux.alibaba.com designates 115.124.30.57 as permitted sender) smtp.mailfrom=baolin.wang@linux.alibaba.com; dmarc=pass (policy=none) header.from=alibaba.com ARC-Seal: i=1; s=arc-20220608; d=hostedemail.com; t=1660801541; a=rsa-sha256; cv=none; b=TE2J7FSNB+P7mXvWOotKdA7u8xrZn1yt+frgMqUTIcW8vjBD52q5WH1ViMxoqpqP7/o3WY +53OsWH51+gP9VGEacVlmGp+Et1mztl4Q1yunmgNjHv/NEf9KiFUYYa2BiH1Ag4hKlSI80 pIRl+vCxVcU2uhu+7X20dEYoMvwIrlo= ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=hostedemail.com; s=arc-20220608; t=1660801541; 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=nZQB263Y1VsqXzQAMe7IMhpDehXTALE9P8T1FHjUJgo=; b=1Y9yWpDUkFJ6ezvuT9L5CRdMbDqyNUQhTZ9twIciXkQ57MaVzZeZ4iz7ZklHy6Vonu9rgu Yp+7Ja1TPQHTiKUAsjvZGTiMMpR6U2icA4znUL6fCyQ8MV0lOheZGvsMmPuALwy5HJsk/x ByxMv1JmUhUzZcNzObKyr4yEpQn6ugU= X-Rspamd-Queue-Id: 7F68A14007A Authentication-Results: imf23.hostedemail.com; dkim=none; spf=pass (imf23.hostedemail.com: domain of baolin.wang@linux.alibaba.com designates 115.124.30.57 as permitted sender) smtp.mailfrom=baolin.wang@linux.alibaba.com; dmarc=pass (policy=none) header.from=alibaba.com X-Rspam-User: X-Rspamd-Server: rspam09 X-Stat-Signature: hwixit8ze73ci6hh7hnm8qtbh4hgdzpx X-HE-Tag: 1660801539-458976 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 1:12 PM, Muchun Song wrote: > > >> On Aug 18, 2022, at 13:07, Baolin Wang wrote: >> >> >> >> 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. > > I am not suggesting you change it to pmd_trans_huge() in this patch, I am just expressing > my curious. At least, it is a little confusing to me. OK. >> >> 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. > > Yep, make sense to me. OK. I can add a cleanup patch in next version. Thanks for your input.