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 9CDFFEE49A6 for ; Mon, 21 Aug 2023 20:21:26 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S230459AbjHUUV0 (ORCPT ); Mon, 21 Aug 2023 16:21:26 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:53414 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S230446AbjHUUVZ (ORCPT ); Mon, 21 Aug 2023 16:21:25 -0400 Received: from dfw.source.kernel.org (dfw.source.kernel.org [139.178.84.217]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 389B711C for ; Mon, 21 Aug 2023 13:21:22 -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 CAEAC63E9A for ; Mon, 21 Aug 2023 20:21:21 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id D9F61C433C7; Mon, 21 Aug 2023 20:21:20 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=linux-foundation.org; s=korg; t=1692649281; bh=UYHFeqSQzpPFRn6m2yxsPjlcReEMpIU+Exeq39DnB8U=; h=Date:From:To:Cc:Subject:In-Reply-To:References:From; b=sLmXwHgFuqqapxRe3+yeZKK7CDPOs5xCFuV15p5m/gNNZUxfaxQNNl1rElZVR4pCi Ppty/+tE0UhCDIXeAfmiFjsuaVq69GF8A6+zw1hbKjOqCBWxjQu9qN7p4SoNcfxHP9 6URjiAPZPAAlNrGRJwtt4UmKUbSGVe8q8G7B/Moc= Date: Mon, 21 Aug 2023 13:21:19 -0700 From: Andrew Morton To: Qi Zheng Cc: Will Deacon , Qi Zheng , 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: <20230821132119.110668fde87a29443f0bff28@linux-foundation.org> In-Reply-To: References: <20230810093241.1181142-1-qi.zheng@linux.dev> <20230811110311.GB6993@willie-the-truck> <20230811112107.GE6993@willie-the-truck> X-Mailer: Sylpheed 3.8.0beta1 (GTK+ 2.24.33; x86_64-pc-linux-gnu) Mime-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Fri, 11 Aug 2023 19:28:41 +0800 Qi Zheng wrote: > Will Deacon 于2023年8月11日 周五19:21写道： > > > 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. > > > Ah, this is init_mm, not user mm, page_table_check does not care about this > case. It's unclear where we stand with this patch. An ack or a nack, please?