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=-5.4 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 33267C43214 for ; Wed, 4 Aug 2021 21:03:22 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 186EA6104F for ; Wed, 4 Aug 2021 21:03:22 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S239981AbhHDVDd (ORCPT ); Wed, 4 Aug 2021 17:03:33 -0400 Received: from mga01.intel.com ([192.55.52.88]:50993 "EHLO mga01.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S231771AbhHDVDT (ORCPT ); Wed, 4 Aug 2021 17:03:19 -0400 X-IronPort-AV: E=McAfee;i="6200,9189,10066"; a="235972196" X-IronPort-AV: E=Sophos;i="5.84,295,1620716400"; d="scan'208";a="235972196" Received: from fmsmga003.fm.intel.com ([10.253.24.29]) by fmsmga101.fm.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 04 Aug 2021 14:03:05 -0700 X-IronPort-AV: E=Sophos;i="5.84,295,1620716400"; d="scan'208";a="512230737" Received: from bguvendi-mobl.amr.corp.intel.com (HELO skuppusw-mobl5.amr.corp.intel.com) ([10.212.99.93]) by fmsmga003-auth.fm.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 04 Aug 2021 14:03:05 -0700 Subject: Re: [PATCH v5 11/12] x86/tdx: Don't write CSTAR MSR on Intel To: Sean Christopherson Cc: Thomas Gleixner , Ingo Molnar , Borislav Petkov , Peter Zijlstra , Andy Lutomirski , Peter H Anvin , Dave Hansen , Tony Luck , Dan Williams , Andi Kleen , Kirill Shutemov , Kuppuswamy Sathyanarayanan , x86@kernel.org, linux-kernel@vger.kernel.org References: <20210804181329.2899708-1-sathyanarayanan.kuppuswamy@linux.intel.com> <20210804181329.2899708-12-sathyanarayanan.kuppuswamy@linux.intel.com> From: "Kuppuswamy, Sathyanarayanan" Message-ID: <4c1ee7b9-9941-fdc4-73f5-3d2ef0530556@linux.intel.com> Date: Wed, 4 Aug 2021 14:03:03 -0700 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:78.0) Gecko/20100101 Firefox/78.0 Thunderbird/78.11.0 MIME-Version: 1.0 In-Reply-To: Content-Type: text/plain; charset=utf-8; format=flowed Content-Language: en-US Content-Transfer-Encoding: 7bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 8/4/21 11:31 AM, Sean Christopherson wrote: >> On Intel CPUs writing the CSTAR MSR is not really needed. Syscalls >> from 32bit work using SYSENTER and 32bit SYSCALL is an illegal opcode. >> But the kernel did write it anyways even though it was ignored by >> the CPU. Inside a TDX guest this actually leads to a #GP. While the #GP >> is caught and recovered from, it prints an ugly message at boot. >> Do not write the CSTAR MSR on Intel CPUs. > Not that it really matters, but... > > Is #GP the actual TDX-Module behavior? If so, isn't that a contradiction with No, #GP is triggered by guest. > respect to the TDX-Module architecture? It says: > > guest TD access violations to MSRs can cause a #GP(0) in most cases where the > MSR is enumerated as inaccessible by the Intel TDX module via CPUID > virtualization. In other cases, guest TD access violations to MSRs can cause > a #VE. > > Given that there is no dedicated CPUID flag for CSTAR and CSTAR obviously exists > on Intel CPUs, I don't see how the TDX-Module can possible enumerate CSTAR as > being inaccessible. > > Regardless of #GP versus #VE, "Table 16.2 MSR Virtualization" needs to state the > actual behavior. Even in this case, it will trigger #VE. But since CSTAR MSR is not supported, write to it will fail and leads to #VE fault. File: arch/x86/kernel/traps.c 1183 DEFINE_IDTENTRY(exc_virtualization_exception) 1201 if (!ret) 1202 ret = tdg_handle_virtualization_exception(regs, &ve); 1203 /* 1204 * If tdg_handle_virtualization_exception() could not process 1205 * it successfully, treat it as #GP(0) and handle it. 1206 */ 1207 if (ret) 1208 ve_raise_fault(regs, 0); -- Sathyanarayanan Kuppuswamy Linux Kernel Developer