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 161D9C433C1 for ; Mon, 29 Mar 2021 22:03:26 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id D386E61969 for ; Mon, 29 Mar 2021 22:03:25 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S230520AbhC2WCx (ORCPT ); Mon, 29 Mar 2021 18:02:53 -0400 Received: from mga09.intel.com ([134.134.136.24]:5623 "EHLO mga09.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S230143AbhC2WCT (ORCPT ); Mon, 29 Mar 2021 18:02:19 -0400 IronPort-SDR: 2jnA7upKnQGw93cxm+TjsNtlLlPlsvJFlw01dz+HPZNN4a9s8TGVpz3YuvjpTf6dkXX1uQWBTI qrpsVPmcZvWw== X-IronPort-AV: E=McAfee;i="6000,8403,9938"; a="191732194" X-IronPort-AV: E=Sophos;i="5.81,289,1610438400"; d="scan'208";a="191732194" Received: from fmsmga008.fm.intel.com ([10.253.24.58]) by orsmga102.jf.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 29 Mar 2021 15:02:16 -0700 IronPort-SDR: DWa6HJpI4lAblDWxe9lvVPFuI4lvE9fzszO51yVQvttuU0WQ75PXwXgYQ5iwjzbKUNeaeDSnan V6RxM2Bfz/HQ== X-IronPort-AV: E=Sophos;i="5.81,289,1610438400"; d="scan'208";a="411293782" Received: from jmwolcot-mobl.amr.corp.intel.com (HELO [10.209.158.84]) ([10.209.158.84]) by fmsmga008-auth.fm.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 29 Mar 2021 15:02:15 -0700 Subject: Re: [PATCH v2 1/1] x86/tdx: Handle MWAIT, MONITOR and WBINVD To: "Kuppuswamy, Sathyanarayanan" , Peter Zijlstra , Andy Lutomirski Cc: Andi Kleen , Kirill Shutemov , Kuppuswamy Sathyanarayanan , Dan Williams , Raj Ashok , Sean Christopherson , linux-kernel@vger.kernel.org References: <91C0F6F1-B8C3-4130-B903-C63CD4B87F3F@amacapital.net> <498f078c-5196-a608-7f1a-8425ff056135@intel.com> <8e02ce39-f672-e652-b314-418b7ec5f52a@linux.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: <8e02ce39-f672-e652-b314-418b7ec5f52a@linux.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 3/29/21 2:55 PM, Kuppuswamy, Sathyanarayanan wrote: >> >> MONITOR is a privileged instruction, right?  So we can only end up in >> here if the kernel screws up and isn't reading CPUID correctly, right? >> >> That dosen't seem to me like something we want to suppress.  This needs >> a warning, at least.  I assume that having a MONITOR instruction >> immediately return doesn't do any harm. > Agree. Since we are not supposed to come here, I will use BUG. "This is unexpected" is a WARN()able offense. "This is unexpected and might be corrupting data" is where we want to use BUG(). Does broken MONITOR risk data corruption? >>> +    case EXIT_REASON_MWAIT_INSTRUCTION: >>> +        /* MWAIT is supressed, not supposed to reach here. */ >>> +        WARN(1, "MWAIT unexpected #VE Exception\n"); >>> +        return -EFAULT; >> >> How is MWAIT "supppressed"? > I am clearing the MWAIT feature flag in early init code. We should also > disable this feature in firmware. setup_clear_cpu_cap(X86_FEATURE_MWAIT); I'd be more explicit about that. Maybe even reference the code that clears the X86_FEATURE.