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=-14.8 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH,MAILING_LIST_MULTI,NICE_REPLY_A, SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED,USER_AGENT_SANE_1 autolearn=unavailable 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 BC33AC43461 for ; Thu, 10 Sep 2020 10:23:51 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 806262078E for ; Thu, 10 Sep 2020 10:23:51 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1725971AbgIJKXv (ORCPT ); Thu, 10 Sep 2020 06:23:51 -0400 Received: from foss.arm.com ([217.140.110.172]:60372 "EHLO foss.arm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1725913AbgIJKXp (ORCPT ); Thu, 10 Sep 2020 06:23:45 -0400 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 B4B941063; Thu, 10 Sep 2020 03:23:44 -0700 (PDT) Received: from [192.168.1.179] (unknown [172.31.20.19]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id 2D4693F68F; Thu, 10 Sep 2020 03:23:43 -0700 (PDT) Subject: Re: [PATCH v9 09/29] arm64: mte: Clear the tags when a page is mapped in user-space with PROT_MTE To: Catalin Marinas , linux-arm-kernel@lists.infradead.org Cc: linux-mm@kvack.org, linux-arch@vger.kernel.org, Will Deacon , Dave P Martin , Vincenzo Frascino , Szabolcs Nagy , Kevin Brodsky , Andrey Konovalov , Peter Collingbourne , Andrew Morton References: <20200904103029.32083-1-catalin.marinas@arm.com> <20200904103029.32083-10-catalin.marinas@arm.com> From: Steven Price Message-ID: <5c2ebe16-2ac9-6cff-3456-6d8ac96b5fb7@arm.com> Date: Thu, 10 Sep 2020 11:23:33 +0100 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: <20200904103029.32083-10-catalin.marinas@arm.com> Content-Type: text/plain; charset=utf-8; format=flowed Content-Language: en-GB Content-Transfer-Encoding: 7bit Sender: linux-arch-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-arch@vger.kernel.org On 04/09/2020 11:30, Catalin Marinas wrote: > Pages allocated by the kernel are not guaranteed to have the tags > zeroed, especially as the kernel does not (yet) use MTE itself. To > ensure the user can still access such pages when mapped into its address > space, clear the tags via set_pte_at(). A new page flag - PG_mte_tagged > (PG_arch_2) - is used to track pages with valid allocation tags. > > Since the zero page is mapped as pte_special(), it won't be covered by > the above set_pte_at() mechanism. Clear its tags during early MTE > initialisation. > > Co-developed-by: Steven Price > Signed-off-by: Steven Price > Signed-off-by: Catalin Marinas > Cc: Will Deacon [...] > diff --git a/arch/arm64/lib/mte.S b/arch/arm64/lib/mte.S > new file mode 100644 > index 000000000000..a36705640086 > --- /dev/null > +++ b/arch/arm64/lib/mte.S > @@ -0,0 +1,34 @@ > +/* SPDX-License-Identifier: GPL-2.0-only */ > +/* > + * Copyright (C) 2020 ARM Ltd. > + */ > +#include > + > +#include > +#include > + > + .arch armv8.5-a+memtag > + > +/* > + * multitag_transfer_size - set \reg to the block size that is accessed by the > + * LDGM/STGM instructions. > + */ > + .macro multitag_transfer_size, reg, tmp > + mrs_s \reg, SYS_GMID_EL1 > + ubfx \reg, \reg, #SYS_GMID_EL1_BS_SHIFT, #SYS_GMID_EL1_BS_SIZE > + mov \tmp, #4 > + lsl \reg, \tmp, \reg > + .endm > + > +/* > + * Clear the tags in a page > + * x0 - address of the page to be cleared > + */ > +SYM_FUNC_START(mte_clear_page_tags) > + multitag_transfer_size x1, x2 > +1: stgm xzr, [x0] > + add x0, x0, x1 > + tst x0, #(PAGE_SIZE - 1) > + b.ne 1b > + ret > +SYM_FUNC_END(mte_clear_page_tags) > Could the value of SYS_GMID_EL1 vary between CPUs and do we therefore need a preempt_disable() around mte_clear_page_tags() (and other functions in later patches)? Steve