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 F2A84C433E0 for ; Tue, 23 Jun 2020 17:40:28 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id C8F9A206B7 for ; Tue, 23 Jun 2020 17:40:28 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1592934028; bh=dsXPPeg6cIv+Pkd9+QstYAyB8a1dU40W6wd0csB7Qx4=; h=From:To:Cc:Subject:Date:In-Reply-To:References:List-ID:From; b=eshJDGJlRd4km/9+n5sPMY/L+MAdXOdtRfiC1h/SjTcbIBnYez2xaJ5Sfy90Edov5 GbIsdHehwX4WC/gjEfobHGTWNAmaMfObC4WsX3dVvY7cE9iYn590R+CU/hW2VliW9z RT/rhOsmou3/iYZydF1f08GLw728vTUYAConqAyk= Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S2387513AbgFWRgN (ORCPT ); Tue, 23 Jun 2020 13:36:13 -0400 Received: from mail.kernel.org ([198.145.29.99]:32994 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S2387475AbgFWRgI (ORCPT ); Tue, 23 Jun 2020 13:36:08 -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 9077A207F9; Tue, 23 Jun 2020 17:36:06 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1592933767; bh=dsXPPeg6cIv+Pkd9+QstYAyB8a1dU40W6wd0csB7Qx4=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=ObhNY9VVv3F68h1LcST8Xl0tSaKg9LHx3+MyEX8dgDCXyahTmW/2ACpDJAgzW9pmW uvpXkaz8XMWwdpbkm/clPidXLrTaV7c2DK1EcB3ZTcqD8bmubSc0C4eAcPMdIFsnw3 muCDGEbSzk74CacxipR1v5trYbugxjueSoUYlIlE= From: Sasha Levin To: linux-kernel@vger.kernel.org, stable@vger.kernel.org Cc: Dave Martin , Will Deacon , Sasha Levin , linux-arm-kernel@lists.infradead.org Subject: [PATCH AUTOSEL 5.4 06/24] arm64/sve: Eliminate data races on sve_default_vl Date: Tue, 23 Jun 2020 13:35:41 -0400 Message-Id: <20200623173559.1355728-6-sashal@kernel.org> X-Mailer: git-send-email 2.25.1 In-Reply-To: <20200623173559.1355728-1-sashal@kernel.org> References: <20200623173559.1355728-1-sashal@kernel.org> MIME-Version: 1.0 X-stable: review X-Patchwork-Hint: Ignore Content-Transfer-Encoding: 8bit Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@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 1765e5284994f..d8895251a2aac 100644 --- a/arch/arm64/kernel/fpsimd.c +++ b/arch/arm64/kernel/fpsimd.c @@ -12,6 +12,7 @@ #include #include #include +#include #include #include #include @@ -119,10 +120,20 @@ 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; int __ro_after_init sve_max_virtualisable_vl = SVE_VL_MIN; @@ -345,7 +356,7 @@ 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), @@ -362,7 +373,7 @@ 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; } @@ -869,7 +880,7 @@ 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)); bitmap_andnot(tmp_map, sve_vq_partial_map, sve_vq_map, SVE_VQ_MAX); @@ -890,7 +901,7 @@ void __init sve_setup(void) 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()); /* KVM decides whether to support mismatched systems. Just warn here: */ if (sve_max_virtualisable_vl < sve_max_vl) @@ -1030,13 +1041,13 @@ 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