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 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 578F4C433F5 for ; Tue, 5 Oct 2021 14:20:17 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 371B960F4B for ; Tue, 5 Oct 2021 14:20:17 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S236028AbhJEOWG (ORCPT ); Tue, 5 Oct 2021 10:22:06 -0400 Received: from mga09.intel.com ([134.134.136.24]:64219 "EHLO mga09.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S235524AbhJEOWC (ORCPT ); Tue, 5 Oct 2021 10:22:02 -0400 X-IronPort-AV: E=McAfee;i="6200,9189,10128"; a="225650874" X-IronPort-AV: E=Sophos;i="5.85,349,1624345200"; d="scan'208";a="225650874" Received: from fmsmga008.fm.intel.com ([10.253.24.58]) by orsmga102.jf.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 05 Oct 2021 07:10:03 -0700 X-IronPort-AV: E=Sophos;i="5.85,349,1624345200"; d="scan'208";a="523785654" Received: from ftbalow-mobl.amr.corp.intel.com (HELO [10.212.210.174]) ([10.212.210.174]) by fmsmga008-auth.fm.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 05 Oct 2021 07:10:02 -0700 Subject: Re: [PATCH v8 02/11] x86/tdx: Introduce INTEL_TDX_GUEST config option To: Sathyanarayanan Kuppuswamy Natarajan , Randy Dunlap Cc: Kuppuswamy Sathyanarayanan , Thomas Gleixner , Ingo Molnar , Borislav Petkov , x86@kernel.org, Paolo Bonzini , David Hildenbrand , Andrea Arcangeli , Josh Poimboeuf , Juergen Gross , Deep Shah , VMware Inc , Vitaly Kuznetsov , Wanpeng Li , Jim Mattson , Joerg Roedel , Peter H Anvin , Tony Luck , Dan Williams , Andi Kleen , Kirill Shutemov , Sean Christopherson , Linux Kernel Mailing List References: <20211005025205.1784480-1-sathyanarayanan.kuppuswamy@linux.intel.com> <20211005025205.1784480-3-sathyanarayanan.kuppuswamy@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: 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 10/5/21 6:29 AM, Sathyanarayanan Kuppuswamy Natarajan wrote: > On Mon, Oct 4, 2021 at 9:53 PM Randy Dunlap wrote: >> On 10/4/21 7:51 PM, Kuppuswamy Sathyanarayanan wrote: >>> diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig >>> index 2b2a9639d8ae..c42dd8a2d1f4 100644 >>> --- a/arch/x86/Kconfig >>> +++ b/arch/x86/Kconfig >>> @@ -865,6 +865,20 @@ config ACRN_GUEST >>> IOT with small footprint and real-time features. More details can be >>> found inhttps://projectacrn.org/. >>> >>> +config INTEL_TDX_GUEST >>> + bool "Intel Trusted Domain eXtensions Guest Support" >>> + depends on X86_64 && CPU_SUP_INTEL && PARAVIRT >>> + depends on SECURITY >>> + select X86_X2APIC >> Apparently some Intel CPUs don't have the x2apic feature, since the >> Kconfig help text for X86_X2APIC says: >> >> This enables x2apic support on CPUs that have this feature. >> >> so how is it safe to set/enable/select that kconfig symbol? >> >> Will the x2apic code just safely not work if the h/w feature is >> missing? > For the TDX guest, x2apic will be emulated. So it will exist in our > case. Even if x2apic or TDX guest is not supported by CPU, it will > boot just fine. This doesn't really explain the "select X86_X2APIC", though. You just said that TDX doesn't *require* X2APIC. So, why is it being selected? What is the specific connection between TDX and X2APIC?