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=-5.3 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,NICE_REPLY_A,SPF_HELO_NONE, SPF_PASS,USER_AGENT_SANE_1 autolearn=no 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 AA705C432BE for ; Tue, 3 Aug 2021 21:38:33 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 922F4604AC for ; Tue, 3 Aug 2021 21:38:33 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S232311AbhHCVin (ORCPT ); Tue, 3 Aug 2021 17:38:43 -0400 Received: from mga01.intel.com ([192.55.52.88]:54314 "EHLO mga01.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S232073AbhHCVim (ORCPT ); Tue, 3 Aug 2021 17:38:42 -0400 X-IronPort-AV: E=McAfee;i="6200,9189,10065"; a="235737342" X-IronPort-AV: E=Sophos;i="5.84,292,1620716400"; d="scan'208";a="235737342" Received: from fmsmga008.fm.intel.com ([10.253.24.58]) by fmsmga101.fm.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 03 Aug 2021 14:38:29 -0700 X-IronPort-AV: E=Sophos;i="5.84,292,1620716400"; d="scan'208";a="479838238" Received: from fratthe-mobl.amr.corp.intel.com (HELO [10.209.8.96]) ([10.209.8.96]) by fmsmga008-auth.fm.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 03 Aug 2021 14:38:28 -0700 Subject: Re: [PATCH v9 25/26] intel_idle/amx: Add SPR support with XTILEDATA capability To: "Bae, Chang Seok" Cc: Borislav Petkov , "Lutomirski, Andy" , Thomas Gleixner , Ingo Molnar , the arch/x86 maintainers , "Brown, Len" , "Macieira, Thiago" , "Liu, Jing2" , "Shankar, Ravi V" , Linux Kernel Mailing List , "linux-pm@vger.kernel.org" References: <20210730145957.7927-1-chang.seok.bae@intel.com> <20210730145957.7927-26-chang.seok.bae@intel.com> <9660CC2A-F09F-49BF-B5CF-7288B726C88E@intel.com> From: Dave Hansen Autocrypt: addr=dave.hansen@intel.com; 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Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.10.0 MIME-Version: 1.0 In-Reply-To: <9660CC2A-F09F-49BF-B5CF-7288B726C88E@intel.com> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 8bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 8/3/21 2:32 PM, Bae, Chang Seok wrote: >>> +static inline void idle_tile(void) >>> +{ >>> + if (boot_cpu_has(X86_FEATURE_XGETBV1) && (xgetbv(1) & XFEATURE_MASK_XTILE)) { >>> + tile_release(); >>> + fpregs_deactivate(¤t->thread.fpu); >>> + } >>> +} >> This isn't obviously safe code. There's a window in there when we have >> bogus, destroyed FPU register state but where we might be rescheduled. >> >> I would assume that preempt is off *somewhere* in this, but it would be >> nice to make sure of that, or at least mention the requirement for it to >> be off before this code is safe. > I can see preempt_disable() in this path: > > $kernel/sched/idle.c::play_idle_precise() > --> preempt_disable() > ... > --> do_idle() > --> cpuidle_idle_call() > --> call_cpuidle() > --> $drivers/cpuidle/cpuidle.c::cpuidle_enter() > --> cpuidle_enter_state() > --> target_state->enter() > --> $drivers/idle/intel_idle.c::intel_idle_tile() > --> idle_tile() > ... > --> preempt_enable() OK, that's good. Can we comment about the preempt requirement somewhere? Or, maybe add a !in_atomic() warning? Also, should this have something like a fpregs_state_valid() check? If the registers are invalid, should this be calling tile_release()?