From patchwork Thu May 27 15:34:48 2021 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Robin Murphy X-Patchwork-Id: 12284911 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=-17.1 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,URIBL_BLOCKED, USER_AGENT_GIT 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 756C6C47089 for ; Thu, 27 May 2021 16:57:48 +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 30CE2611F0 for ; Thu, 27 May 2021 16:57:48 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 30CE2611F0 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:MIME-Version:References:In-Reply-To: Message-Id:Date:Subject:Cc:To:From:Reply-To:Content-ID:Content-Description: Resent-Date:Resent-From:Resent-Sender:Resent-To:Resent-Cc:Resent-Message-ID: List-Owner; bh=O6lTPtxFE2kHkFoYkdqqWnH6wGI53hVZqxMu7mZmoYE=; b=hXL8b0WG5OwDCW 7TlBfLjsAwQE8SNoqVsU7M2juUTYgBQPvd1Q9DVRe3gSOT+oK7bvl9RbOY0o9ptogA0UQ7a+WD00r oIUW34sRn50uXWfa9cFgb2gY7Cev9iFJs9CZZOOmF0XwqTbWddo7DIe4B/+faka5s5MU9B8GpMha8 xhTLj4c4CW0g7/0iqnOY5gJNL9hZcgDqb32ZN/5hseyvdG7jGavcdLr02Q2tgkK6vMl9dQfG6Aznn UD+i9ScPmctWBfjbVLeXssxfCXQfhCivp5ZuR9wsgK/lsXWZnk4VgX570FQwwfilnByAbgtrJdrXl iErqpQisqIjKYSseQsMg==; Received: from localhost ([::1] helo=bombadil.infradead.org) by bombadil.infradead.org with esmtp (Exim 4.94.2 #2 (Red Hat Linux)) id 1lmJIZ-007psG-BM; Thu, 27 May 2021 16:55:56 +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 1lmI2N-007GMB-23 for linux-arm-kernel@lists.infradead.org; Thu, 27 May 2021 15:35:08 +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 1525F16F8; Thu, 27 May 2021 08:35:04 -0700 (PDT) Received: from e110467-lin.cambridge.arm.com (e110467-lin.cambridge.arm.com [10.1.196.41]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPA id 643123F73B; Thu, 27 May 2021 08:35:03 -0700 (PDT) From: Robin Murphy To: will@kernel.org, catalin.marinas@arm.com Cc: linux-arm-kernel@lists.infradead.org, mark.rutland@arm.com Subject: [PATCH v2 8/8] arm64: Rewrite __arch_clear_user() Date: Thu, 27 May 2021 16:34:48 +0100 Message-Id: <1cbd78b12c076a8ad4656a345811cfb9425df0b3.1622128527.git.robin.murphy@arm.com> X-Mailer: git-send-email 2.21.0.dirty In-Reply-To: References: MIME-Version: 1.0 X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20210527_083507_193359_64DB1A2D X-CRM114-Status: GOOD ( 11.74 ) 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: , Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+linux-arm-kernel=archiver.kernel.org@lists.infradead.org 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. Apparently some folks examine large reads from /dev/zero closely enough to notice the loop being hot, so align it per the other critical loops (presumably around a typical instruction fetch granularity). Reviewed-by: Mark Rutland Signed-off-by: Robin Murphy --- arch/arm64/lib/clear_user.S | 47 +++++++++++++++++++++---------------- 1 file changed, 27 insertions(+), 20 deletions(-) diff --git a/arch/arm64/lib/clear_user.S b/arch/arm64/lib/clear_user.S index af9afcbec92c..a7efb2ad2a1c 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 +16,33 @@ * * Alignment fixed up by hardware. */ + + .p2align 4 + // Alignment is for the loop, but since the prologue (including BTI) + // is also 16 bytes we can keep any padding outside the function 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 +50,8 @@ 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