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=-16.8 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_CR_TRAILER,INCLUDES_PATCH, MAILING_LIST_MULTI,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 61FB9C63799 for ; Thu, 22 Jul 2021 17:53:16 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 4834B6140C for ; Thu, 22 Jul 2021 17:53:16 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S230208AbhGVRMk (ORCPT ); Thu, 22 Jul 2021 13:12:40 -0400 Received: from foss.arm.com ([217.140.110.172]:58010 "EHLO foss.arm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S230075AbhGVRMe (ORCPT ); Thu, 22 Jul 2021 13:12:34 -0400 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 5706D11FB; Thu, 22 Jul 2021 10:53:09 -0700 (PDT) Received: from e113632-lin.cambridge.arm.com (e113632-lin.cambridge.arm.com [10.1.194.46]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPA id 4030B3F73D; Thu, 22 Jul 2021 10:53:07 -0700 (PDT) From: Valentin Schneider To: linux-kernel@vger.kernel.org, linux-arm-kernel@lists.infradead.org, linux-rt-users@vger.kernel.org, x86@kernel.org Cc: Catalin Marinas , Will Deacon , Thomas Gleixner , Steven Rostedt , Daniel Bristot de Oliveira , "Peter Zijlstra (Intel)" , Ingo Molnar , Borislav Petkov , "H. Peter Anvin" , Mark Brown , Dave Martin , Ard Biesheuvel Subject: [PATCH 3/3] arm64/fpsimd: Fix FPSIMD context handling vs PREEMPT_RT Date: Thu, 22 Jul 2021 18:51:57 +0100 Message-Id: <20210722175157.1367122-4-valentin.schneider@arm.com> X-Mailer: git-send-email 2.25.1 In-Reply-To: <20210722175157.1367122-1-valentin.schneider@arm.com> References: <20210722175157.1367122-1-valentin.schneider@arm.com> MIME-Version: 1.0 Content-Transfer-Encoding: 8bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Running v5.13-rt1 on my arm64 Juno board triggers: [ 11.337654] WARNING: CPU: 4 PID: 1 at arch/arm64/kernel/fpsimd.c:296 task_fpsimd_load (arch/arm64/kernel/fpsimd.c:296 (discriminator 1)) [ 11.337692] Modules linked in: [ 11.337705] CPU: 4 PID: 1 Comm: init Not tainted 5.13.0-rt1 #52 [ 11.337719] Hardware name: ARM Juno development board (r0) (DT) [ 11.337727] pstate: 40000005 (nZcv daif -PAN -UAO -TCO BTYPE=--) [ 11.337740] pc : task_fpsimd_load (arch/arm64/kernel/fpsimd.c:296 (discriminator 1)) [ 11.337755] lr : task_fpsimd_load (arch/arm64/kernel/fpsimd.c:296 (discriminator 3)) [ 11.337769] sp : ffff800012f4bdd0 [ 11.337775] x29: ffff800012f4bdd0 x28: ffff000800160000 x27: 0000000000000000 [ 11.337797] x26: 0000000000000000 x25: 0000000000000000 x24: ffff0008001606f0 [ 11.337816] x23: ffff000800160000 x22: ffff000800160700 x21: ffff000800160000 [ 11.337837] x20: ffff800012f4beb0 x19: 0000000000000008 x18: 000000000000c9a0 [ 11.337857] x17: 00000000ae3495d5 x16: 000000000000c9a0 x15: ffff80001240e128 [ 11.337878] x14: ffff8000124b0128 x13: 000000000000000a x12: ffff80001205e5f0 [ 11.337898] x11: 0000000000000000 x10: ffff800011a37d28 x9 : 0000000000000050 [ 11.337917] x8 : ffff000800160000 x7 : 0000000000000002 x6 : 0000000000000000 [ 11.337937] x5 : 0000000000000000 x4 : 0000000000000000 x3 : 0000000000000000 [ 11.337956] x2 : 0000000000000008 x1 : 0000000000000000 x0 : 0000000000000000 [ 11.337975] Call trace: [ 11.337980] task_fpsimd_load (arch/arm64/kernel/fpsimd.c:296 (discriminator 1)) [ 11.337996] fpsimd_restore_current_state (arch/arm64/kernel/fpsimd.c:1186) [ 11.338012] do_notify_resume (./arch/arm64/include/asm/daifflags.h:28 arch/arm64/kernel/signal.c:947) [ 11.338032] work_pending (arch/arm64/kernel/entry.S:839) [ 11.338045] irq event stamp: 1228377 [ 11.338051] hardirqs last enabled at (1228375): _raw_spin_unlock_irqrestore (./include/linux/spinlock_api_smp.h:160 kernel/locking/spinlock.c:194) [ 11.338076] hardirqs last disabled at (1228377): el1_dbg (arch/arm64/kernel/entry-common.c:144 arch/arm64/kernel/entry-common.c:234) [ 11.338098] softirqs last enabled at (1227024): __local_bh_enable_ip (./arch/arm64/include/asm/irqflags.h:85 kernel/softirq.c:262) [ 11.338121] softirqs last disabled at (1228376): fpsimd_restore_current_state (./include/linux/bottom_half.h:19 arch/arm64/kernel/fpsimd.c:183 arch/arm64/kernel/fpsimd.c:1182) This is caused by local_bh_disable() not disabling preemption under CONFIG_PREEMPT_RT, which fails have_cpu_fpsimd_context(). The per-CPU access safety proved by the CONFIG_PREEMPT_RT version of local_bh_disable() is not sufficient here, as we end up with both preemption and IRQs enabled when running do_notify_resume(). This means we can hit: el0_sync `\ do_notify_resume() `\ fpsimd_restore_current_state() ~~> el1_irq `\ preempt_schedule_irq() `\ fpsimd_thread_switch() IOW we *really* need to disable preemption here, even on CONFIG_PREEMPT_RT. The preempt_{enable, disable}_bh() helpers exist to handle this exact case, so use them here. This is spiritually close to: cba08c5dc6dc ("x86/fpu: Make kernel FPU protection RT friendly") Signed-off-by: Valentin Schneider --- arch/arm64/kernel/fpsimd.c | 6 ++++-- 1 file changed, 4 insertions(+), 2 deletions(-) diff --git a/arch/arm64/kernel/fpsimd.c b/arch/arm64/kernel/fpsimd.c index 9bf86cd7b605..0c66ea0dd97e 100644 --- a/arch/arm64/kernel/fpsimd.c +++ b/arch/arm64/kernel/fpsimd.c @@ -177,10 +177,12 @@ static void __get_cpu_fpsimd_context(void) * * The double-underscore version must only be called if you know the task * can't be preempted. + * + * Disabling preemption prevents nesting via fpsimd_thread_switch(). */ static void get_cpu_fpsimd_context(void) { - local_bh_disable(); + preempt_disable_bh(); __get_cpu_fpsimd_context(); } @@ -201,7 +203,7 @@ static void __put_cpu_fpsimd_context(void) static void put_cpu_fpsimd_context(void) { __put_cpu_fpsimd_context(); - local_bh_enable(); + preempt_enable_bh(); } static bool have_cpu_fpsimd_context(void) -- 2.25.1