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 X-Spam-Level: X-Spam-Status: No, score=-8.3 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH,MAILING_LIST_MULTI,NICE_REPLY_A, SPF_HELO_NONE,SPF_PASS,USER_AGENT_SANE_1 autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id D1FB4C2D0A3 for ; Fri, 6 Nov 2020 11:43:20 +0000 (UTC) Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by mail.kernel.org (Postfix) with ESMTP id 263A2206DB for ; Fri, 6 Nov 2020 11:43:19 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 263A2206DB Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=arm.com Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=owner-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix) id 277D66B005C; Fri, 6 Nov 2020 06:43:19 -0500 (EST) Received: by kanga.kvack.org (Postfix, from userid 40) id 1FF806B005D; Fri, 6 Nov 2020 06:43:19 -0500 (EST) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 0C75B6B0068; Fri, 6 Nov 2020 06:43:19 -0500 (EST) X-Delivered-To: linux-mm@kvack.org Received: from forelay.hostedemail.com (smtprelay0177.hostedemail.com [216.40.44.177]) by kanga.kvack.org (Postfix) with ESMTP id D09DC6B005C for ; Fri, 6 Nov 2020 06:43:18 -0500 (EST) Received: from smtpin28.hostedemail.com (10.5.19.251.rfc1918.com [10.5.19.251]) by forelay03.hostedemail.com (Postfix) with ESMTP id 57C228249980 for ; Fri, 6 Nov 2020 11:43:18 +0000 (UTC) X-FDA: 77453807676.28.brass26_4f080f1272d2 Received: from filter.hostedemail.com (10.5.16.251.rfc1918.com [10.5.16.251]) by smtpin28.hostedemail.com (Postfix) with ESMTP id 372806C16 for ; Fri, 6 Nov 2020 11:43:18 +0000 (UTC) X-HE-Tag: brass26_4f080f1272d2 X-Filterd-Recvd-Size: 4340 Received: from foss.arm.com (foss.arm.com [217.140.110.172]) by imf42.hostedemail.com (Postfix) with ESMTP for ; Fri, 6 Nov 2020 11:43:17 +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 B9E07147A; Fri, 6 Nov 2020 03:43:16 -0800 (PST) Received: from [10.37.12.46] (unknown [10.37.12.46]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id 565C13F719; Fri, 6 Nov 2020 03:43:14 -0800 (PST) Subject: Re: [PATCH v8 28/43] arm64: mte: Reset the page tag in page->flags To: Catalin Marinas , Andrey Konovalov Cc: Will Deacon , Dmitry Vyukov , Andrey Ryabinin , Alexander Potapenko , Marco Elver , Evgenii Stepanov , Branislav Rankov , Kevin Brodsky , Andrew Morton , kasan-dev@googlegroups.com, linux-arm-kernel@lists.infradead.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org References: <20201105155859.GA30030@gaia> From: Vincenzo Frascino Message-ID: <01a55e00-0d82-7e62-cc40-c282149dbb08@arm.com> Date: Fri, 6 Nov 2020 11:46:15 +0000 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.10.0 MIME-Version: 1.0 In-Reply-To: <20201105155859.GA30030@gaia> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 7bit 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: Hi Catalin, On 11/5/20 3:59 PM, Catalin Marinas wrote: > On Thu, Nov 05, 2020 at 12:18:43AM +0100, Andrey Konovalov wrote: >> diff --git a/arch/arm64/kernel/mte.c b/arch/arm64/kernel/mte.c >> index 8f99c65837fd..06ba6c923ab7 100644 >> --- a/arch/arm64/kernel/mte.c >> +++ b/arch/arm64/kernel/mte.c >> @@ -34,6 +34,7 @@ static void mte_sync_page_tags(struct page *page, pte_t *ptep, bool check_swap) >> return; >> } >> >> + page_kasan_tag_reset(page); >> mte_clear_page_tags(page_address(page)); > > I think we need an smp_wmb() between setting the flags and clearing the > actual tags. If another threads reads page->flags and builds a tagged > address out of it (see page_to_virt) there's an address dependency to > the actual memory access. However, on the current thread, we don't > guarantee that the new page->flags are visible before the tags were > updated. > Indeed, and I will add a comment as well to explain why. >> } >> >> diff --git a/arch/arm64/mm/copypage.c b/arch/arm64/mm/copypage.c >> index 70a71f38b6a9..348f4627da08 100644 >> --- a/arch/arm64/mm/copypage.c >> +++ b/arch/arm64/mm/copypage.c >> @@ -22,6 +22,7 @@ void copy_highpage(struct page *to, struct page *from) >> copy_page(kto, kfrom); >> >> if (system_supports_mte() && test_bit(PG_mte_tagged, &from->flags)) { >> + page_kasan_tag_reset(to); >> set_bit(PG_mte_tagged, &to->flags); >> mte_copy_page_tags(kto, kfrom); > > Nitpick: move page_kasan_tag_reset() just above mte_copy_page_tags() for > consistency with the other places where PG_mte_tagged is set before or > after the actual tag setting. > Fine, I will add it to the next iteration. >> } >> diff --git a/arch/arm64/mm/mteswap.c b/arch/arm64/mm/mteswap.c >> index c52c1847079c..0e7eccbe598a 100644 >> --- a/arch/arm64/mm/mteswap.c >> +++ b/arch/arm64/mm/mteswap.c >> @@ -53,6 +53,7 @@ bool mte_restore_tags(swp_entry_t entry, struct page *page) >> if (!tags) >> return false; >> >> + page_kasan_tag_reset(page); >> mte_restore_page_tags(page_address(page), tags); I just realized based on your comment above that we need smp_wmb() here as well. I will add it with a comment as well. > > There is another mte_restore_page_tags() caller in hibernate.c. That one > doesn't need page_kasan_tag_reset() since the page->flags would have > been already restored but please add a comment in that file why its not > needed. > Yes I will do, I agree on the reasoning, I will report it in the comments. -- Regards, Vincenzo