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 7A982EE4996 for ; Tue, 22 Aug 2023 09:58:56 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S234537AbjHVJ64 (ORCPT ); Tue, 22 Aug 2023 05:58:56 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:39768 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S231879AbjHVJ6z (ORCPT ); Tue, 22 Aug 2023 05:58:55 -0400 Received: from dfw.source.kernel.org (dfw.source.kernel.org [139.178.84.217]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 02D721A1 for ; Tue, 22 Aug 2023 02:58:54 -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 8D1CB635ED for ; Tue, 22 Aug 2023 09:58:53 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id 1659EC433C8; Tue, 22 Aug 2023 09:58:50 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1692698332; bh=sVhI0MwQkWiaY9ZR0rZ894LsScW3MR+I1sFldvIieKA=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=Gb6SCw3ct7+U5PyNUDKDZtox3L7LrfOJa1QWQ3ZpygAuiBicNU2/d0m8v24Z6Jvbq 9IFtI5hEOvJUS5dL0nxlcGMF5cTmSf0H/km9MtFvhOVXh4ucX4bmcmlJZ+d9GF4bhe 6itsB4aIKQIQlPmWLZhCJ6kxdNsnwrM3NEsimqsweAW2fJ+9C9Owyocd7fJJPpNSaN UNTMnfrKZW5/9wvHbqgflwKPoIq508SUYHL3psSxMFKnmwOFPWEx5Y7TUgRTWrPfpy xRx4zY+IrOEFkTCftINpvLLEYe6m78IeZduMtnx/7kk3ruy7OznYnuMOunCxjaWfSY mf5214Q5Exa2w== Date: Tue, 22 Aug 2023 10:58:47 +0100 From: Will Deacon To: Andrew Morton Cc: Qi Zheng , 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: <20230822095847.GA20667@willie-the-truck> References: <20230810093241.1181142-1-qi.zheng@linux.dev> <20230811110311.GB6993@willie-the-truck> <20230811112107.GE6993@willie-the-truck> <20230821132119.110668fde87a29443f0bff28@linux-foundation.org> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <20230821132119.110668fde87a29443f0bff28@linux-foundation.org> User-Agent: Mutt/1.10.1 (2018-07-13) Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Mon, Aug 21, 2023 at 01:21:19PM -0700, Andrew Morton wrote: > 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? Sorry Andrew, I saw you'd queued it so I marked it as "done" on my list. I think it's fine: Acked-by: Will Deacon Will