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 95CCFC001DB for ; Fri, 11 Aug 2023 11:22:06 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S236384AbjHKLWF (ORCPT ); Fri, 11 Aug 2023 07:22:05 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:57316 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S236434AbjHKLVr (ORCPT ); Fri, 11 Aug 2023 07:21:47 -0400 Received: from dfw.source.kernel.org (dfw.source.kernel.org [IPv6:2604:1380:4641:c500::1]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 198811FE1 for ; Fri, 11 Aug 2023 04:21:14 -0700 (PDT) Received: from smtp.kernel.org (relay.kernel.org [52.25.139.140]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature RSA-PSS (2048 bits)) (No client certificate requested) by dfw.source.kernel.org (Postfix) with ESMTPS id 9A5B663184 for ; Fri, 11 Aug 2023 11:21:13 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id 5EFFDC433C9; Fri, 11 Aug 2023 11:21:11 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1691752873; bh=8iO5ssaC++/QeuKpj5WA1omKjZ55tlXWJLExPQldY/c=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=H+Lejx63MILxcvLOE+PXzKkhIa1ZB2LbJtvCU2LJSQxUOQIvJ1PkLnvFir5Q3kR3y zMqqHR4wCe1A+1iaaW9NvFlo3CU5u0mZSWEmSzfs9ZEzSwhBOKuOXxEMGnBefOcz5U PgbubM91fJzFi4neJvIP1SWRWzSsSRTM3kTbkDviHX+Qf69u4i4xB9JsXdO2OTa612 lTpqxLBrL15OYXUdgoPofsSzzMqhsSkmClvj0rHhfr4XS5yBxEioLjgXZvUGFRqxlu StZKrKC01KQu8aqmfYrS0IEckC/87gxNiWEA68AgJVEX3sZOWcdIP+5WjT2tcG+fSR GLWuwntI4YmNA== Date: Fri, 11 Aug 2023 12:21:07 +0100 From: Will Deacon To: Qi Zheng Cc: Qi Zheng , akpm@linux-foundation.org, catalin.marinas@arm.com, linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org, muchun.song@linux.dev, pasha.tatashin@soleen.com, wangkefeng.wang@huawei.co Subject: Re: [PATCH] arm64: mm: use ptep_clear() instead of pte_clear() in clear_flush() Message-ID: <20230811112107.GE6993@willie-the-truck> References: <20230810093241.1181142-1-qi.zheng@linux.dev> <20230811110311.GB6993@willie-the-truck> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: User-Agent: Mutt/1.10.1 (2018-07-13) Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Fri, Aug 11, 2023 at 07:16:20PM +0800, Qi Zheng wrote: > Will Deacon <[1]will@kernel.org>于2023年8月11日 周五19:03写道： > > On Thu, Aug 10, 2023 at 09:32:41AM +0000, Qi Zheng wrote: > > From: Qi Zheng <[2]zhengqi.arch@bytedance.com> > > > > In clear_flush(), the original pte may be a present entry, so we > should > > use ptep_clear() to let page_table_check track the pte clearing > operation, > > otherwise it may cause false positive in subsequent set_pte_at(). > > Isn't this true for most users of pte_clear()? There are some in the > core > code, so could they trigger the false positive as well? > > No, the PTE entry in other places where pte_clear() is used is non-present > PTE.  > The page_table_check does not does track the pte operation in this case, > so it will not cause false positives. Are you sure? For example, the call from flush_all_zero_pkmaps() in highmem.c really looks like it's clearing a valid entry. Not that arm64 cares about highmem, but still. Will