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=-14.1 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 4D313C47082 for ; Wed, 26 May 2021 13:35:18 +0000 (UTC) Received: from bombadil.infradead.org (bombadil.infradead.org [198.137.202.133]) (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 10C35613C3 for ; Wed, 26 May 2021 13:35:18 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 10C35613C3 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=bombadil.20210309; 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=daQCMtRPqHdzqnnZR/pJUi3LbwDj16iGLPNPk2vS/Us=; b=swwZo5wTGmYpc5 oZPgY04sdvSFnjLHdW5nf2SiGl9Hh+JwufoNOLcUFDES7VzJQQY3TiY7C95QrKVX3VKkIpqxxD7Up GL2q6bzWh6wN2U/xFgTVwLezHV9a6G2svWXj6th7x7RRF/gyiI5YO7QUcXl/HfDXgKi111sy+FnYp C7KyKKpDvUybAAGQ/Zhf77IzouPE4ZuHuEDs/05DbFn5cQFYOhznXZDKac4SmqPadLCtrk9SJKf6Q hz4jds0QiELpeYZr6cBNiAyax4GnSMoT88OGHUSLAvQDthC/3lzlslO6JfCcb6DAuqh4+dN6NX5e6 DDhLPuKXZVWXKCCr9rFA==; Received: from localhost ([::1] helo=bombadil.infradead.org) by bombadil.infradead.org with esmtp (Exim 4.94.2 #2 (Red Hat Linux)) id 1lltf4-00ET71-Ow; Wed, 26 May 2021 13:33:27 +0000 Received: from foss.arm.com ([217.140.110.172]) by bombadil.infradead.org with esmtp (Exim 4.94.2 #2 (Red Hat Linux)) id 1llrW8-00DTRO-8t for linux-arm-kernel@lists.infradead.org; Wed, 26 May 2021 11:16:06 +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 4A4111516; Wed, 26 May 2021 04:15:59 -0700 (PDT) Received: from C02TD0UTHF1T.local (unknown [10.57.40.5]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id 293053F73B; Wed, 26 May 2021 04:15:57 -0700 (PDT) Date: Wed, 26 May 2021 12:15:55 +0100 From: Mark Rutland To: Robin Murphy Cc: will@kernel.org, catalin.marinas@arm.com, linux-arm-kernel@lists.infradead.org Subject: Re: [PATCH v2] arm64: Rewrite __arch_clear_user() Message-ID: <20210526111555.GB3806@C02TD0UTHF1T.local> References: <76a1700b0316b50fb5881da603f2daf3c81468f4.1620738177.git.robin.murphy@arm.com> MIME-Version: 1.0 Content-Disposition: inline In-Reply-To: X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20210526_041604_404429_F7D8F1CE X-CRM114-Status: GOOD ( 20.51 ) 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 Fri, May 14, 2021 at 12:57:07PM +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. 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, while > also allowing the exception fixup to return an accurate result. > > Signed-off-by: Robin Murphy > --- > > v2: Tweak exception fixup to be exact > > arch/arm64/lib/clear_user.S | 44 ++++++++++++++++++++----------------- > 1 file changed, 24 insertions(+), 20 deletions(-) > > diff --git a/arch/arm64/lib/clear_user.S b/arch/arm64/lib/clear_user.S > index af9afcbec92c..d30c03f6caed 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 Could we note the reason for the alignment in the commit message? IIUC that's for consistency with the other routines. Regardless, this looks good to me. I hand-executed this for `sz` in the range 0 to 7 to make sure the logic and fixups were correct, and that all looks good to me. FWIW: Reviewed-by: Mark Rutland Mark. > SYM_FUNC_START(__arch_clear_user) > - mov x2, x1 // save the size for fixup return > + add x2, x0, x1 > subs x1, x1, #8 > b.mi 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 > +USER(9f, sttr wzr, [x0]) > +USER(8f, sttr wzr, [x2, #-4]) > + mov x0, #0 > + ret > + > +3: tbz x1, #1, 4f > +USER(9f, sttrh wzr, [x0]) > +4: tbz x1, #0, 5f > +USER(7f, sttrb wzr, [x2, #-1]) > 5: mov x0, #0 > ret > SYM_FUNC_END(__arch_clear_user) > @@ -45,6 +47,8 @@ EXPORT_SYMBOL(__arch_clear_user) > > .section .fixup,"ax" > .align 2 > -9: mov x0, x2 // return the original size > +7: sub x0, x2, #5 // Adjust for faulting on the final byte... > +8: add x0, x0, #4 // ...or the second word of the 4-7 byte case > +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