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=-14.4 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_CR_TRAILER, INCLUDES_PATCH,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS 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 51F84C433ED for ; Wed, 12 May 2021 10:51:22 +0000 (UTC) Received: from desiato.infradead.org (desiato.infradead.org [90.155.92.199]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPS id 997BB61183 for ; Wed, 12 May 2021 10:51:21 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 997BB61183 Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=arm.com Authentication-Results: mail.kernel.org; spf=none smtp.mailfrom=linux-arm-kernel-bounces+linux-arm-kernel=archiver.kernel.org@lists.infradead.org DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=lists.infradead.org; s=desiato.20200630; h=Sender:Content-Transfer-Encoding :Content-Type:List-Subscribe:List-Help:List-Post:List-Archive: List-Unsubscribe:List-Id:In-Reply-To:MIME-Version:References:Message-ID: Subject:Cc:To:From:Date:Reply-To:Content-ID:Content-Description:Resent-Date: Resent-From:Resent-Sender:Resent-To:Resent-Cc:Resent-Message-ID:List-Owner; bh=wrVjJ9r4ZQQ+08oWLL8EzASBxR0LfCWihgWbIHAYijc=; b=QtJAGVobL9lU3VFwOzpXh2G32 uukh/8NkT5j7Fm0OFZ7szCBryqPolFv83UuuiLi63JySyrqEhwb6OmYrUiEFX4yK3AkjM9+ZMgUXG 8IrjcrO6oCXDmWjoz1Ga7/PTX3vKGxFbSVcbcPxcX5UmfvmyJ6j0DEfrrBMCbrsFAeGtJ5y/UHQff ZbKQF96i1x2X6LS15PJtJcp3n2xyvEdmrn9CbkJQfuMk7TEX73b4pAA6T7MzXwY5IrrqA8fbZPAkL PLPYERDw4OEBpFV1XBVHbf7iPJri0+EA9Jp48K9sgE1XeZCTa5rhgXFyP7dBGG2J0EQo1lelJI9Rx 76cp6FnLA==; Received: from localhost ([::1] helo=desiato.infradead.org) by desiato.infradead.org with esmtp (Exim 4.94 #2 (Red Hat Linux)) id 1lgmQ7-002YVK-61; Wed, 12 May 2021 10:48:51 +0000 Received: from bombadil.infradead.org ([2607:7c80:54:e::133]) by desiato.infradead.org with esmtps (Exim 4.94 #2 (Red Hat Linux)) id 1lgmQ4-002YUw-FU for linux-arm-kernel@desiato.infradead.org; Wed, 12 May 2021 10:48:48 +0000 DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=infradead.org; s=bombadil.20210309; h=In-Reply-To:Content-Type:MIME-Version :References:Message-ID:Subject:Cc:To:From:Date:Sender:Reply-To: Content-Transfer-Encoding:Content-ID:Content-Description; bh=8I0l2NP2rTy6TGayUtXtazCKKgKGSbjBSMQrk4/Es84=; b=Akqwnd1JWMKptj0ZfYhMD+xDwH sKRa02x4GnJnOI8oPhPBL3q2k1g7FTbW3wmE7BVSSJ7KTth2ED7JaWim3yPpztqDom9SoJcjDY6uX 6fWkAGpSTDIjSlqha5+oEW2FS4+XvgFU2ZHhhslVoFYmKacMkYN5aELGydsG79oug117EpxXmTwTE Lv58fdWWMzSbNgsp/t2kqHcnaX3Co9Lgixak7eIIwwe2MFsjJY3cLap4z99tyncKD6v4N+uLFIDjM ILhL5Ly+PeCdQn0XnFDcua8s1GyorEdrNcZij41arsNcFNtaJhTeOIGDGjKSnrhlun9JkQgdWtwzN ZeAWJuFQ==; Received: from foss.arm.com ([217.140.110.172]) by bombadil.infradead.org with esmtp (Exim 4.94 #2 (Red Hat Linux)) id 1lgmQ1-00AINe-BP for linux-arm-kernel@lists.infradead.org; Wed, 12 May 2021 10:48:47 +0000 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 CE0DC31B; Wed, 12 May 2021 03:48:37 -0700 (PDT) Received: from C02TD0UTHF1T.local (unknown [10.57.30.106]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id 413323F719; Wed, 12 May 2021 03:48:36 -0700 (PDT) Date: Wed, 12 May 2021 11:48:33 +0100 From: Mark Rutland To: Robin Murphy Cc: will@kernel.org, catalin.marinas@arm.com, linux-arm-kernel@lists.infradead.org, yangyingliang@huawei.com, shenkai8@huawei.com Subject: Re: [PATCH 8/8] arm64: Rewrite __arch_clear_user() Message-ID: <20210512104833.GD88854@C02TD0UTHF1T.local> References: <76a1700b0316b50fb5881da603f2daf3c81468f4.1620738177.git.robin.murphy@arm.com> MIME-Version: 1.0 Content-Disposition: inline In-Reply-To: <76a1700b0316b50fb5881da603f2daf3c81468f4.1620738177.git.robin.murphy@arm.com> X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20210512_034845_508206_3DACFF72 X-CRM114-Status: GOOD ( 22.43 ) X-BeenThere: linux-arm-kernel@lists.infradead.org X-Mailman-Version: 2.1.34 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+linux-arm-kernel=archiver.kernel.org@lists.infradead.org On Tue, May 11, 2021 at 05:12:38PM +0100, Robin Murphy wrote: > Now that we're always using STTR variants rather than abstracting two > different addressing modes, the user_ldst macro here is frankly more > obfuscating than helpful. FWIW, I completely agree; the user_ldst macros are a historical artifact and I'm happy to see them go! > Rewrite __arch_clear_user() with regular > USER() annotations so that it's clearer what's going on, and take the > opportunity to minimise the branchiness in the most common paths, which > also allows the exception fixup to return a more accurate result. IIUC this isn't always accurate for the {4,2,1}-byte cases; example below. I'm not sure whether that's intentional since the commit message says "more accurate" rather than "accurate". > > Signed-off-by: Robin Murphy > --- > arch/arm64/lib/clear_user.S | 42 +++++++++++++++++++------------------ > 1 file changed, 22 insertions(+), 20 deletions(-) > > diff --git a/arch/arm64/lib/clear_user.S b/arch/arm64/lib/clear_user.S > index af9afcbec92c..1005345b4066 100644 > --- a/arch/arm64/lib/clear_user.S > +++ b/arch/arm64/lib/clear_user.S > @@ -1,12 +1,9 @@ > /* SPDX-License-Identifier: GPL-2.0-only */ > /* > - * Based on arch/arm/lib/clear_user.S > - * > - * Copyright (C) 2012 ARM Ltd. > + * Copyright (C) 2021 Arm Ltd. > */ > -#include > > -#include > +#include > #include > > .text > @@ -19,25 +16,30 @@ > * > * Alignment fixed up by hardware. > */ > + .p2align 4 > SYM_FUNC_START(__arch_clear_user) Say we're called with size in x1 == 0x7 > - mov x2, x1 // save the size for fixup return > + add x2, x0, x1 > subs x1, x1, #8 > b.mi 2f ... here we'll skip to the 4-byte case at 2f ... > 1: > -user_ldst 9f, sttr, xzr, x0, 8 > +USER(9f, sttr xzr, [x0]) > + add x0, x0, #8 > subs x1, x1, #8 > - b.pl 1b > -2: adds x1, x1, #4 > - b.mi 3f > -user_ldst 9f, sttr, wzr, x0, 4 > - sub x1, x1, #4 > -3: adds x1, x1, #2 > - b.mi 4f > -user_ldst 9f, sttrh, wzr, x0, 2 > - sub x1, x1, #2 > -4: adds x1, x1, #1 > - b.mi 5f > -user_ldst 9f, sttrb, wzr, x0, 0 > + b.hi 1b > +USER(9f, sttr xzr, [x2, #-8]) > + mov x0, #0 > + ret > + > +2: tbz x1, #2, 3f ... bit 2 is non-zero, so we continue ... > +USER(9f, sttr wzr, [x0]) ... and if this faults, the fixup will report the correct address ... > +USER(9f, sttr wzr, [x2, #-4]) ... but if this faults, teh fixup handler will report that we didn't copy all 7 bytes, rather than just the last 3, since we didn't update x0 after the first 4-byte STTR. We could update x0 inline, or add separate fixup handlers to account for that out-of-line. If we think that under-estimating is fine, I reckon it'd be worth a comment to make that clear. Thanks, Mark. > + mov x0, #0 > + ret > + > +3: tbz x1, #1, 4f > +USER(9f, sttrh wzr, [x0]) > +4: tbz x1, #0, 5f > +USER(9f, sttrb wzr, [x2, #-1]) > 5: mov x0, #0 > ret > SYM_FUNC_END(__arch_clear_user) > @@ -45,6 +47,6 @@ EXPORT_SYMBOL(__arch_clear_user) > > .section .fixup,"ax" > .align 2 > -9: mov x0, x2 // return the original size > +9: sub x0, x2, x0 > ret > .previous > -- > 2.21.0.dirty > > > _______________________________________________ > linux-arm-kernel mailing list > linux-arm-kernel@lists.infradead.org > http://lists.infradead.org/mailman/listinfo/linux-arm-kernel _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel