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=-10.1 required=3.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY, SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED,USER_AGENT_GIT 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 EE2ADC433E3 for ; Mon, 29 Jun 2020 20:07:42 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id CFCDA207D0 for ; Mon, 29 Jun 2020 20:07:42 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1593461262; bh=cN7Ws5kFubXu9Ze739Ig/VKXejpZSMxSGXVMrzTa6eU=; h=From:To:Cc:Subject:Date:In-Reply-To:References:List-ID:From; b=jUVVQn0X15pgCgBiegQKdD4Fr7ITC8akFzFe/ocUVTHUmzCjSL6WpvDYiQ5yZIWXP JYeHuSwqV0Y+tN01OeWKsJ+Pavad+z7A3Yy/jhvocRSYqS6uFiIsrlF1tUgh9GUolv U3it8lvRoCJ3k/njF7J5nMtWgIjOC09wv5AN7h24= Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1732955AbgF2TaY (ORCPT ); Mon, 29 Jun 2020 15:30:24 -0400 Received: from mail.kernel.org ([198.145.29.99]:40594 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1732882AbgF2TaV (ORCPT ); Mon, 29 Jun 2020 15:30:21 -0400 Received: from sasha-vm.mshome.net (c-73-47-72-35.hsd1.nh.comcast.net [73.47.72.35]) (using TLSv1.2 with cipher ECDHE-RSA-AES128-GCM-SHA256 (128/128 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPSA id D1BE925285; Mon, 29 Jun 2020 15:36:34 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1593444995; bh=cN7Ws5kFubXu9Ze739Ig/VKXejpZSMxSGXVMrzTa6eU=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=0pgpET9zrMoInm+oUnSKxk1nLF9tKeAKNDdY/Ae5TUQH0PMEWQMoTMQHDEST18ilp l6ija1OTbFTfBd6nqBpT9yK2lmIipepRyM3cnOSuQrzaNt2hanq8lzcSoLe2bgwVCS +irXn5o05bjVtMIyk7VnOKvHWw7oO+tlEXgt0Exc= From: Sasha Levin To: linux-kernel@vger.kernel.org, stable@vger.kernel.org Cc: Dave Martin , Will Deacon , Sasha Levin Subject: [PATCH 4.19 095/131] arm64/sve: Eliminate data races on sve_default_vl Date: Mon, 29 Jun 2020 11:34:26 -0400 Message-Id: <20200629153502.2494656-96-sashal@kernel.org> X-Mailer: git-send-email 2.25.1 In-Reply-To: <20200629153502.2494656-1-sashal@kernel.org> References: <20200629153502.2494656-1-sashal@kernel.org> MIME-Version: 1.0 X-KernelTest-Patch: http://kernel.org/pub/linux/kernel/v4.x/stable-review/patch-4.19.131-rc1.gz X-KernelTest-Tree: git://git.kernel.org/pub/scm/linux/kernel/git/stable/linux-stable-rc.git X-KernelTest-Branch: linux-4.19.y X-KernelTest-Patches: git://git.kernel.org/pub/scm/linux/kernel/git/stable/stable-queue.git X-KernelTest-Version: 4.19.131-rc1 X-KernelTest-Deadline: 2020-07-01T15:34+00:00 X-stable: review X-Patchwork-Hint: Ignore Content-Transfer-Encoding: 8bit Sender: stable-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: stable@vger.kernel.org From: Dave Martin [ Upstream commit 1e570f512cbdc5e9e401ba640d9827985c1bea1e ] sve_default_vl can be modified via the /proc/sys/abi/sve_default_vl sysctl concurrently with use, and modified concurrently by multiple threads. Adding a lock for this seems overkill, and I don't want to think any more than necessary, so just define wrappers using READ_ONCE()/ WRITE_ONCE(). This will avoid the possibility of torn accesses and repeated loads and stores. There's no evidence yet that this is going wrong in practice: this is just hygiene. For generic sysctl users, it would be better to build this kind of thing into the sysctl common code somehow. Reported-by: Will Deacon Signed-off-by: Dave Martin Link: https://lore.kernel.org/r/1591808590-20210-3-git-send-email-Dave.Martin@arm.com [will: move set_sve_default_vl() inside #ifdef to squash allnoconfig warning] Signed-off-by: Will Deacon Signed-off-by: Sasha Levin --- arch/arm64/kernel/fpsimd.c | 25 ++++++++++++++++++------- 1 file changed, 18 insertions(+), 7 deletions(-) diff --git a/arch/arm64/kernel/fpsimd.c b/arch/arm64/kernel/fpsimd.c index 14fdbaa6ee3ab..af59b42973141 100644 --- a/arch/arm64/kernel/fpsimd.c +++ b/arch/arm64/kernel/fpsimd.c @@ -22,6 +22,7 @@ #include #include #include +#include #include #include #include @@ -124,10 +125,20 @@ struct fpsimd_last_state_struct { static DEFINE_PER_CPU(struct fpsimd_last_state_struct, fpsimd_last_state); /* Default VL for tasks that don't set it explicitly: */ -static int sve_default_vl = -1; +static int __sve_default_vl = -1; + +static int get_sve_default_vl(void) +{ + return READ_ONCE(__sve_default_vl); +} #ifdef CONFIG_ARM64_SVE +static void set_sve_default_vl(int val) +{ + WRITE_ONCE(__sve_default_vl, val); +} + /* Maximum supported vector length across all CPUs (initially poisoned) */ int __ro_after_init sve_max_vl = SVE_VL_MIN; /* Set of available vector lengths, as vq_to_bit(vq): */ @@ -311,7 +322,7 @@ static int sve_proc_do_default_vl(struct ctl_table *table, int write, loff_t *ppos) { int ret; - int vl = sve_default_vl; + int vl = get_sve_default_vl(); struct ctl_table tmp_table = { .data = &vl, .maxlen = sizeof(vl), @@ -328,7 +339,7 @@ static int sve_proc_do_default_vl(struct ctl_table *table, int write, if (!sve_vl_valid(vl)) return -EINVAL; - sve_default_vl = find_supported_vector_length(vl); + set_sve_default_vl(find_supported_vector_length(vl)); return 0; } @@ -772,12 +783,12 @@ void __init sve_setup(void) * For the default VL, pick the maximum supported value <= 64. * VL == 64 is guaranteed not to grow the signal frame. */ - sve_default_vl = find_supported_vector_length(64); + set_sve_default_vl(find_supported_vector_length(64)); pr_info("SVE: maximum available vector length %u bytes per vector\n", sve_max_vl); pr_info("SVE: default vector length %u bytes per vector\n", - sve_default_vl); + get_sve_default_vl()); sve_efi_setup(); } @@ -914,13 +925,13 @@ void fpsimd_flush_thread(void) * vector length configured: no kernel task can become a user * task without an exec and hence a call to this function. * By the time the first call to this function is made, all - * early hardware probing is complete, so sve_default_vl + * early hardware probing is complete, so __sve_default_vl * should be valid. * If a bug causes this to go wrong, we make some noise and * try to fudge thread.sve_vl to a safe value here. */ vl = current->thread.sve_vl_onexec ? - current->thread.sve_vl_onexec : sve_default_vl; + current->thread.sve_vl_onexec : get_sve_default_vl(); if (WARN_ON(!sve_vl_valid(vl))) vl = SVE_VL_MIN; -- 2.25.1