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 6EAACC433F5 for ; Sat, 9 Oct 2021 05:38:31 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 53C4360FC1 for ; Sat, 9 Oct 2021 05:38:31 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S244593AbhJIFkZ (ORCPT ); Sat, 9 Oct 2021 01:40:25 -0400 Received: from mga04.intel.com ([192.55.52.120]:29189 "EHLO mga04.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S244395AbhJIFkB (ORCPT ); Sat, 9 Oct 2021 01:40:01 -0400 X-IronPort-AV: E=McAfee;i="6200,9189,10131"; a="225410075" X-IronPort-AV: E=Sophos;i="5.85,360,1624345200"; d="scan'208";a="225410075" Received: from fmsmga002.fm.intel.com ([10.253.24.26]) by fmsmga104.fm.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 08 Oct 2021 22:38:05 -0700 X-IronPort-AV: E=Sophos;i="5.85,360,1624345200"; d="scan'208";a="569280264" Received: from dmsojoza-mobl3.amr.corp.intel.com (HELO skuppusw-desk1.amr.corp.intel.com) ([10.251.135.62]) by fmsmga002-auth.fm.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 08 Oct 2021 22:38:04 -0700 From: Kuppuswamy Sathyanarayanan To: 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 Cc: Peter H Anvin , Dave Hansen , Tony Luck , Dan Williams , Andi Kleen , Kirill Shutemov , Sean Christopherson , Kuppuswamy Sathyanarayanan , linux-kernel@vger.kernel.org Subject: [PATCH v10 10/11] x86/tdx: Don't write CSTAR MSR on Intel Date: Fri, 8 Oct 2021 22:37:46 -0700 Message-Id: <20211009053747.1694419-11-sathyanarayanan.kuppuswamy@linux.intel.com> X-Mailer: git-send-email 2.25.1 In-Reply-To: <20211009053747.1694419-1-sathyanarayanan.kuppuswamy@linux.intel.com> References: <20211009053747.1694419-1-sathyanarayanan.kuppuswamy@linux.intel.com> MIME-Version: 1.0 Content-Transfer-Encoding: 8bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org From: Andi Kleen 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 #VE which in turn will trigger ve_raise_fault() due to failed MSR write. Inside ve_raise_fault() before it recovers from this error, it prints an ugly message at boot. Since such warning message is pointless for CSTAR MSR write failure, add exception to skip CSTAR msr write on Intel CPUs. Signed-off-by: Andi Kleen --- Changes since v9: * None Changes since v8: * None Changes since v7: * None. Changes since v6: * None. Changes since v5: * Fixed commit log as per review comments. arch/x86/kernel/cpu/common.c | 11 +++++++++-- 1 file changed, 9 insertions(+), 2 deletions(-) diff --git a/arch/x86/kernel/cpu/common.c b/arch/x86/kernel/cpu/common.c index 0f8885949e8c..fd10f1044157 100644 --- a/arch/x86/kernel/cpu/common.c +++ b/arch/x86/kernel/cpu/common.c @@ -1758,7 +1758,13 @@ void syscall_init(void) wrmsrl(MSR_LSTAR, (unsigned long)entry_SYSCALL_64); #ifdef CONFIG_IA32_EMULATION - wrmsrl(MSR_CSTAR, (unsigned long)entry_SYSCALL_compat); + /* + * CSTAR is not needed on Intel because it doesn't support + * 32bit SYSCALL, but only SYSENTER. On a TDX guest + * it leads to a #GP. + */ + if (boot_cpu_data.x86_vendor != X86_VENDOR_INTEL) + wrmsrl(MSR_CSTAR, (unsigned long)entry_SYSCALL_compat); /* * This only works on Intel CPUs. * On AMD CPUs these MSRs are 32-bit, CPU truncates MSR_IA32_SYSENTER_EIP. @@ -1770,7 +1776,8 @@ void syscall_init(void) (unsigned long)(cpu_entry_stack(smp_processor_id()) + 1)); wrmsrl_safe(MSR_IA32_SYSENTER_EIP, (u64)entry_SYSENTER_compat); #else - wrmsrl(MSR_CSTAR, (unsigned long)ignore_sysret); + if (boot_cpu_data.x86_vendor != X86_VENDOR_INTEL) + wrmsrl(MSR_CSTAR, (unsigned long)ignore_sysret); wrmsrl_safe(MSR_IA32_SYSENTER_CS, (u64)GDT_ENTRY_INVALID_SEG); wrmsrl_safe(MSR_IA32_SYSENTER_ESP, 0ULL); wrmsrl_safe(MSR_IA32_SYSENTER_EIP, 0ULL); -- 2.25.1