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=-2.8 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,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 E29EDECDFB3 for ; Mon, 16 Jul 2018 07:41:17 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id A48A5206B7 for ; Mon, 16 Jul 2018 07:41:17 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org A48A5206B7 Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=linuxfoundation.org Authentication-Results: mail.kernel.org; spf=none smtp.mailfrom=linux-kernel-owner@vger.kernel.org Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S2388424AbeGPIHR (ORCPT ); Mon, 16 Jul 2018 04:07:17 -0400 Received: from mail.linuxfoundation.org ([140.211.169.12]:47510 "EHLO mail.linuxfoundation.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1728440AbeGPIHQ (ORCPT ); Mon, 16 Jul 2018 04:07:16 -0400 Received: from localhost (LFbn-1-12247-202.w90-92.abo.wanadoo.fr [90.92.61.202]) by mail.linuxfoundation.org (Postfix) with ESMTPSA id B02A9CA1; Mon, 16 Jul 2018 07:41:13 +0000 (UTC) From: Greg Kroah-Hartman To: linux-kernel@vger.kernel.org Cc: Greg Kroah-Hartman , stable@vger.kernel.org, Ard Biesheuvel , Dave Martin , Mark Rutland , Yandong Zhao , Will Deacon Subject: [PATCH 4.14 39/54] arm64: neon: Fix function may_use_simd() return error status Date: Mon, 16 Jul 2018 09:35:36 +0200 Message-Id: <20180716073457.992986671@linuxfoundation.org> X-Mailer: git-send-email 2.18.0 In-Reply-To: <20180716073450.534886211@linuxfoundation.org> References: <20180716073450.534886211@linuxfoundation.org> User-Agent: quilt/0.65 X-stable: review MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 4.14-stable review patch. If anyone has any objections, please let me know. ------------------ From: Yandong Zhao commit 2fd8eb4ad87104c54800ef3cea498c92eb15c78a upstream. It does not matter if the caller of may_use_simd() migrates to another cpu after the call, but it is still important that the kernel_neon_busy percpu instance that is read matches the cpu the task is running on at the time of the read. This means that raw_cpu_read() is not sufficient. kernel_neon_busy may appear true if the caller migrates during the execution of raw_cpu_read() and the next task to be scheduled in on the initial cpu calls kernel_neon_begin(). This patch replaces raw_cpu_read() with this_cpu_read() to protect against this race. Cc: Fixes: cb84d11e1625 ("arm64: neon: Remove support for nested or hardirq kernel-mode NEON") Acked-by: Ard Biesheuvel Reviewed-by: Dave Martin Reviewed-by: Mark Rutland Signed-off-by: Yandong Zhao Signed-off-by: Will Deacon Signed-off-by: Greg Kroah-Hartman --- arch/arm64/include/asm/simd.h | 19 +++++++------------ 1 file changed, 7 insertions(+), 12 deletions(-) --- a/arch/arm64/include/asm/simd.h +++ b/arch/arm64/include/asm/simd.h @@ -29,20 +29,15 @@ DECLARE_PER_CPU(bool, kernel_neon_busy); static __must_check inline bool may_use_simd(void) { /* - * The raw_cpu_read() is racy if called with preemption enabled. - * This is not a bug: kernel_neon_busy is only set when - * preemption is disabled, so we cannot migrate to another CPU - * while it is set, nor can we migrate to a CPU where it is set. - * So, if we find it clear on some CPU then we're guaranteed to - * find it clear on any CPU we could migrate to. - * - * If we are in between kernel_neon_begin()...kernel_neon_end(), - * the flag will be set, but preemption is also disabled, so we - * can't migrate to another CPU and spuriously see it become - * false. + * kernel_neon_busy is only set while preemption is disabled, + * and is clear whenever preemption is enabled. Since + * this_cpu_read() is atomic w.r.t. preemption, kernel_neon_busy + * cannot change under our feet -- if it's set we cannot be + * migrated, and if it's clear we cannot be migrated to a CPU + * where it is set. */ return !in_irq() && !irqs_disabled() && !in_nmi() && - !raw_cpu_read(kernel_neon_busy); + !this_cpu_read(kernel_neon_busy); } #else /* ! CONFIG_KERNEL_MODE_NEON */