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 727CAC38A2D for ; Wed, 26 Oct 2022 08:36:04 +0000 (UTC) Received: by kanga.kvack.org (Postfix) id E264D8E0002; Wed, 26 Oct 2022 04:36:03 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id DD6438E0001; Wed, 26 Oct 2022 04:36:03 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id C9DBD8E0002; Wed, 26 Oct 2022 04:36:03 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from relay.hostedemail.com (smtprelay0010.hostedemail.com [216.40.44.10]) by kanga.kvack.org (Postfix) with ESMTP id B64E38E0001 for ; Wed, 26 Oct 2022 04:36:03 -0400 (EDT) Received: from smtpin10.hostedemail.com (a10.router.float.18 [10.200.18.1]) by unirelay10.hostedemail.com (Postfix) with ESMTP id 85C58C0C17 for ; Wed, 26 Oct 2022 08:36:03 +0000 (UTC) X-FDA: 80062443006.10.68A93D7 Received: from foss.arm.com (foss.arm.com [217.140.110.172]) by imf10.hostedemail.com (Postfix) with ESMTP id 000B5C0038 for ; Wed, 26 Oct 2022 08:36:02 +0000 (UTC) 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 3A25A23A; Wed, 26 Oct 2022 01:36:08 -0700 (PDT) Received: from [10.163.37.85] (unknown [10.163.37.85]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id A5B563F792; Wed, 26 Oct 2022 01:35:58 -0700 (PDT) Message-ID: <3c545133-71aa-9a8d-8a13-09186c4fa767@arm.com> Date: Wed, 26 Oct 2022 14:06:00 +0530 MIME-Version: 1.0 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:102.0) Gecko/20100101 Thunderbird/102.2.2 Subject: Re: [PATCH -next 1/1] mm: hugetlb_vmemmap: Fix WARN_ON in vmemmap_remap_pte Content-Language: en-US To: Muchun Song Cc: Wupeng Ma , Andrew Morton , Mike Kravetz , Muchun Song , Michal Hocko , Oscar Salvador , catalin.marinas@arm.com, Linux Memory Management List , linux-kernel@vger.kernel.org References: <20221025014215.3466904-1-mawupeng1@huawei.com> <614E3E83-1EAB-4C39-AF9C-83C0CCF26218@linux.dev> <35dd51eb-c266-f221-298a-21309c17971a@arm.com> <3D6FDA43-A812-4907-B9C8-C2B25567DBBC@linux.dev> From: Anshuman Khandual In-Reply-To: <3D6FDA43-A812-4907-B9C8-C2B25567DBBC@linux.dev> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=hostedemail.com; s=arc-20220608; t=1666773363; 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=iHufS2whdreYtdhYPJfeojBWCOrpClK1O+A7MBPwaN4=; b=nCVODc606dJ9Y9018bvbZwLODxHiugiyYNzAiZSUZQeqsyIefBf3XGznjtxLjbc+DtaAoQ j5UfzEPGOa94BJFkkegq+Gdipyi3ZFGdC2NXSvv0V4U6XSUph/C3J7wbSdiRBCtFikuTpR pzIPbSq6YFkzAnZytx2tdwrteQ2VAiI= ARC-Authentication-Results: i=1; imf10.hostedemail.com; dkim=none; dmarc=pass (policy=none) header.from=arm.com; spf=pass (imf10.hostedemail.com: domain of anshuman.khandual@arm.com designates 217.140.110.172 as permitted sender) smtp.mailfrom=anshuman.khandual@arm.com ARC-Seal: i=1; s=arc-20220608; d=hostedemail.com; t=1666773363; a=rsa-sha256; cv=none; b=za0kSlZ62NfcX5vum2ym4n9u8++GqtbbTNSulkDFJ5UzK6XNDbkU5BYPCRNM5kFNyCCOAN 5uHFxPY4j7opRuGKvS+BrjG6QZpZ3tNInL4UsjyAAlZkSL4GUw3cjtQWK8+tyIBqHAiAyL 9tIzb/rbsbS5/LD+cAX1wymIbnUQAQo= X-Rspamd-Server: rspam06 X-Rspamd-Queue-Id: 000B5C0038 X-Rspam-User: Authentication-Results: imf10.hostedemail.com; dkim=none; dmarc=pass (policy=none) header.from=arm.com; spf=pass (imf10.hostedemail.com: domain of anshuman.khandual@arm.com designates 217.140.110.172 as permitted sender) smtp.mailfrom=anshuman.khandual@arm.com X-Stat-Signature: 4wrdcd55h8j7qd73pimrsyu6p3grw54s X-HE-Tag: 1666773362-66175 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 10/26/22 12:31, Muchun Song wrote: > > >> On Oct 26, 2022, at 13:06, Anshuman Khandual wrote: >> >> >> >> On 10/25/22 12:06, Muchun Song wrote: >>> >>> >>>> On Oct 25, 2022, at 09:42, Wupeng Ma wrote: >>>> >>>> From: Ma Wupeng >>>> >>>> Commit f41f2ed43ca5 ("mm: hugetlb: free the vmemmap pages associated with >>>> each HugeTLB page") add vmemmap_remap_pte to remap the tail pages as >>>> read-only to catch illegal write operation to the tail page. >>>> >>>> However this will lead to WARN_ON in arm64 in __check_racy_pte_update() >>> >>> Thanks for your finding this issue. >>> >>>> since this may lead to dirty state cleaned. This check is introduced by >>>> commit 2f4b829c625e ("arm64: Add support for hardware updates of the >>>> access and dirty pte bits") and the initial check is as follow: >>>> >>>> BUG_ON(pte_write(*ptep) && !pte_dirty(pte)); >>>> >>>> Since we do need to mark this pte as read-only to catch illegal write >>>> operation to the tail pages, use set_pte to replace set_pte_at to bypass >>>> this check. >>> >>> In theory, the waring does not affect anything since the tail vmemmap >>> pages are supposed to be read-only. So, skipping this check for vmemmap >> >> Tails vmemmap pages are supposed to be read-only, in practice but their >> backing pages do have pte_write() enabled. Otherwise the VM_WARN_ONCE() >> warning would not have triggered. > > Right. > >> >> VM_WARN_ONCE(pte_write(old_pte) && !pte_dirty(pte), >> "%s: racy dirty state clearing: 0x%016llx -> 0x%016llx", >> __func__, pte_val(old_pte), pte_val(pte)); >> >> Also, is not it true that the pte being remapped into a different page >> as read only, than what it had originally (which will be freed up) i.e >> the PFN in 'old_pte' and 'pte' will be different. Hence is there still > > Right. > >> a possibility for a race condition even when the PFN changes ? > > Sorry, I didn't get this question. Did you mean the PTE is changed from > new (pte) to the old one (old_pte) by the hardware because of the update > of dirty bit when a concurrent write operation to the tail vmemmap page? No, but is not vmemmap_remap_pte() reuses walk->reuse_page for all remaining tails pages ? Is not there a PFN change, along with access permission change involved in this remapping process ?