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=-19.2 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,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 E1A15C4743D for ; Tue, 8 Jun 2021 18:04:47 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id CA1AD613AD for ; Tue, 8 Jun 2021 18:04:47 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S234165AbhFHSGj (ORCPT ); Tue, 8 Jun 2021 14:06:39 -0400 Received: from mail.kernel.org ([198.145.29.99]:46232 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S233702AbhFHSGZ (ORCPT ); Tue, 8 Jun 2021 14:06:25 -0400 Received: by mail.kernel.org (Postfix) with ESMTPSA id DAF6E61377; Tue, 8 Jun 2021 18:04:28 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1623175472; bh=DOju4Qkdazocj9FpNAdyJz+fzAXLHJIskweDvyX2/bU=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=OfjBOue9fuzmxPOj/KqDgcNGa3da8OVKKo7EO0duS+WlkqRCrDKbdCxVqPahZvvTb M+JMkvAxtYMsqFvMBljOy5Y9xumEguWoqKouE8auloXnklab3qZ6jqRmZPDsaBxihp IFzw4Dl9QmPzsoM4hz1yODCeXAEWzyXu8mYmMljzl+KH+rk8pN3t7xMZc1UXxdOAm1 ERjxp0gq4jmc6HCW3eSVAPYQRJcJFqmyf3I9FVdTVzmRUk2p9wiWbb736+haSzjhot Lfo24qGPoj+k9iXVdUzo5b2XRSFeGe1itBj+2JWHI9jaYWF6TdjG18GzkR1y80Nih+ dWtl0GHyM6nxw== From: Will Deacon To: linux-arm-kernel@lists.infradead.org Cc: linux-arch@vger.kernel.org, linux-kernel@vger.kernel.org, Will Deacon , Catalin Marinas , Marc Zyngier , Greg Kroah-Hartman , Peter Zijlstra , Morten Rasmussen , Qais Yousef , Suren Baghdasaryan , Quentin Perret , Tejun Heo , Johannes Weiner , Ingo Molnar , Juri Lelli , Vincent Guittot , "Rafael J. Wysocki" , Dietmar Eggemann , Daniel Bristot de Oliveira , Valentin Schneider , Mark Rutland , kernel-team@android.com Subject: [PATCH v9 16/20] arm64: Prevent offlining first CPU with 32-bit EL0 on mismatched system Date: Tue, 8 Jun 2021 19:03:09 +0100 Message-Id: <20210608180313.11502-17-will@kernel.org> X-Mailer: git-send-email 2.20.1 In-Reply-To: <20210608180313.11502-1-will@kernel.org> References: <20210608180313.11502-1-will@kernel.org> MIME-Version: 1.0 Content-Transfer-Encoding: 8bit Precedence: bulk List-ID: X-Mailing-List: linux-arch@vger.kernel.org If we want to support 32-bit applications, then when we identify a CPU with mismatched 32-bit EL0 support we must ensure that we will always have an active 32-bit CPU available to us from then on. This is important for the scheduler, because is_cpu_allowed() will be constrained to 32-bit CPUs for compat tasks and forced migration due to a hotplug event will hang if no 32-bit CPUs are available. On detecting a mismatch, prevent offlining of either the mismatching CPU if it is 32-bit capable, or find the first active 32-bit capable CPU otherwise. Reviewed-by: Catalin Marinas Signed-off-by: Will Deacon --- arch/arm64/kernel/cpufeature.c | 25 ++++++++++++++++++++++++- 1 file changed, 24 insertions(+), 1 deletion(-) diff --git a/arch/arm64/kernel/cpufeature.c b/arch/arm64/kernel/cpufeature.c index d735dd13167b..55a58933e3b2 100644 --- a/arch/arm64/kernel/cpufeature.c +++ b/arch/arm64/kernel/cpufeature.c @@ -2877,15 +2877,38 @@ void __init setup_cpu_features(void) static int enable_mismatched_32bit_el0(unsigned int cpu) { + /* + * The first 32-bit-capable CPU we detected and so can no longer + * be offlined by userspace. -1 indicates we haven't yet onlined + * a 32-bit-capable CPU. + */ + static int lucky_winner = -1; + struct cpuinfo_arm64 *info = &per_cpu(cpu_data, cpu); bool cpu_32bit = id_aa64pfr0_32bit_el0(info->reg_id_aa64pfr0); if (cpu_32bit) { cpumask_set_cpu(cpu, cpu_32bit_el0_mask); static_branch_enable_cpuslocked(&arm64_mismatched_32bit_el0); - setup_elf_hwcaps(compat_elf_hwcaps); } + if (cpumask_test_cpu(0, cpu_32bit_el0_mask) == cpu_32bit) + return 0; + + if (lucky_winner >= 0) + return 0; + + /* + * We've detected a mismatch. We need to keep one of our CPUs with + * 32-bit EL0 online so that is_cpu_allowed() doesn't end up rejecting + * every CPU in the system for a 32-bit task. + */ + lucky_winner = cpu_32bit ? cpu : cpumask_any_and(cpu_32bit_el0_mask, + cpu_active_mask); + get_cpu_device(lucky_winner)->offline_disabled = true; + setup_elf_hwcaps(compat_elf_hwcaps); + pr_info("Asymmetric 32-bit EL0 support detected on CPU %u; CPU hot-unplug disabled on CPU %u\n", + cpu, lucky_winner); return 0; } -- 2.32.0.rc1.229.g3e70b5a671-goog