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=-15.6 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,NICE_REPLY_A,SPF_HELO_NONE,SPF_PASS, URIBL_BLOCKED,USER_AGENT_SANE_1 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 A088BC4707F for ; Thu, 27 May 2021 13:36:09 +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 65ABC61059 for ; Thu, 27 May 2021 13:36:09 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 65ABC61059 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-Type: Content-Transfer-Encoding:List-Subscribe:List-Help:List-Post:List-Archive: List-Unsubscribe:List-Id:In-Reply-To:MIME-Version:Date:Message-ID:From: References:Cc:To:Subject:Reply-To:Content-ID:Content-Description:Resent-Date: Resent-From:Resent-Sender:Resent-To:Resent-Cc:Resent-Message-ID:List-Owner; bh=F6zAHdJ9dbI/mzFe5evmc9ftGDlwCHjp9xZmDS3G28M=; b=RMZY/OLZZR3cqllJ3UfZGwvxSB MYO9vTjg9Aix2Gs9OnTeCFHN5z3IE+3DEkMgqXYxWACvd6NwdT5ITBpuuXMub0McvBHIT/faZxzOh 8Aac8o3J4TZwEdu5XR5YOs3FszCWa40tKBtmNs7t14Q/pPCC27EzRK8C0eWZJKbpABgQv6EuqxPx8 gElhZ9taDnf/7zh2+pqZgUfuWvcY0UFK3sH+Xq7LqOT9wKA4RqNHrCp1oI4tgGpeMlE40VZ+3o8Si AAmKE0U6JWoxte3jdPMlf0DDBUodtSfuTfo45Wqk3MvCW5ZMTa61FJs17fIUKppK6UAe8vw2SAaIa 2p6eQKEA==; Received: from localhost ([::1] helo=bombadil.infradead.org) by bombadil.infradead.org with esmtp (Exim 4.94.2 #2 (Red Hat Linux)) id 1lmG91-006JEH-70; Thu, 27 May 2021 13:33:52 +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 1lmFzw-006EXE-P3 for linux-arm-kernel@lists.infradead.org; Thu, 27 May 2021 13:24:30 +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 9A4BE14FF; Thu, 27 May 2021 06:24:23 -0700 (PDT) Received: from [10.57.73.64] (unknown [10.57.73.64]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id E12483F73D; Thu, 27 May 2021 06:24:22 -0700 (PDT) Subject: Re: [PATCH v2] arm64: Rewrite __arch_clear_user() To: Mark Rutland Cc: will@kernel.org, catalin.marinas@arm.com, linux-arm-kernel@lists.infradead.org References: <76a1700b0316b50fb5881da603f2daf3c81468f4.1620738177.git.robin.murphy@arm.com> <20210526111555.GB3806@C02TD0UTHF1T.local> From: Robin Murphy Message-ID: Date: Thu, 27 May 2021 14:24:17 +0100 User-Agent: Mozilla/5.0 (Windows NT 10.0; rv:78.0) Gecko/20100101 Thunderbird/78.10.1 MIME-Version: 1.0 In-Reply-To: <20210526111555.GB3806@C02TD0UTHF1T.local> Content-Language: en-GB X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20210527_062428_963663_A71DE09C X-CRM114-Status: GOOD ( 22.99 ) 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-Transfer-Encoding: 7bit Content-Type: text/plain; charset="us-ascii"; Format="flowed" Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+linux-arm-kernel=archiver.kernel.org@lists.infradead.org On 2021-05-26 12:15, Mark Rutland wrote: > 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. Yes, it's alignment for the loop as per the other routines - since the prologue (including BTI landing pad) is the same length as we're aligning to, then we may as well let any padding fall outside the function. I'll comment that in the code, since it might be a bit subtle. > 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 Thanks! I'll clarify the relevant commit messages about the relicensing as well and repost the series shortly, unless there are any further comments. Cheers, Robin. > > 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