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=-7.3 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, HK_RANDOM_FROM,INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_HELO_NONE, SPF_PASS,USER_AGENT_SANE_1 autolearn=unavailable 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 2DDF5C433DF for ; Thu, 21 May 2020 08:03:16 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 0C09E206B6 for ; Thu, 21 May 2020 08:03:16 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728521AbgEUIDM (ORCPT ); Thu, 21 May 2020 04:03:12 -0400 Received: from mga12.intel.com ([192.55.52.136]:28815 "EHLO mga12.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726208AbgEUIDL (ORCPT ); Thu, 21 May 2020 04:03:11 -0400 IronPort-SDR: xQeBQhK3A+gGS6Pc8JQnynuhDZqd9dkP982zUL3PgrEL36LCdzuwJzRZwJMiifMgdQw5Ic/Ptu C2wC17KSescg== X-Amp-Result: SKIPPED(no attachment in message) X-Amp-File-Uploaded: False Received: from orsmga005.jf.intel.com ([10.7.209.41]) by fmsmga106.fm.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 21 May 2020 01:03:11 -0700 IronPort-SDR: mdzcInu+nHsVQ4gPEiQktmNc+k7tQTG45ABEezbov/pH+l/dqt+52wfsKxEk+ChpVmvmCzvpUu E2rh4t+IddYA== X-IronPort-AV: E=Sophos;i="5.73,417,1583222400"; d="scan'208";a="440355710" Received: from unknown (HELO [10.239.13.122]) ([10.239.13.122]) by orsmga005-auth.jf.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 21 May 2020 01:03:09 -0700 Subject: Re: [PATCH 2/2] kvm/x86: don't expose MSR_IA32_UMWAIT_CONTROL unconditionally To: Maxim Levitsky , Vitaly Kuznetsov , kvm@vger.kernel.org Cc: linux-kernel@vger.kernel.org References: <20200520160740.6144-1-mlevitsk@redhat.com> <20200520160740.6144-3-mlevitsk@redhat.com> <874ksatvkr.fsf@vitty.brq.redhat.com> <0c1a0c81bbdcfaf4ae9af545f4a38439b1a56d11.camel@redhat.com> From: Xiaoyao Li Message-ID: Date: Thu, 21 May 2020 16:03:07 +0800 User-Agent: Mozilla/5.0 (Windows NT 10.0; WOW64; rv:68.0) Gecko/20100101 Thunderbird/68.8.0 MIME-Version: 1.0 In-Reply-To: <0c1a0c81bbdcfaf4ae9af545f4a38439b1a56d11.camel@redhat.com> Content-Type: text/plain; charset=utf-8; format=flowed Content-Language: en-US Content-Transfer-Encoding: 7bit Sender: kvm-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: kvm@vger.kernel.org On 5/21/2020 12:56 AM, Maxim Levitsky wrote: > On Wed, 2020-05-20 at 18:33 +0200, Vitaly Kuznetsov wrote: >> Maxim Levitsky writes: >> >>> This msr is only available when the host supports WAITPKG feature. >>> >>> This breaks a nested guest, if the L1 hypervisor is set to ignore >>> unknown msrs, because the only other safety check that the >>> kernel does is that it attempts to read the msr and >>> rejects it if it gets an exception. >>> >>> Fixes: 6e3ba4abce KVM: vmx: Emulate MSR IA32_UMWAIT_CONTROL >>> >>> Signed-off-by: Maxim Levitsky >>> --- >>> arch/x86/kvm/x86.c | 4 ++++ >>> 1 file changed, 4 insertions(+) >>> >>> diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c >>> index fe3a24fd6b263..9c507b32b1b77 100644 >>> --- a/arch/x86/kvm/x86.c >>> +++ b/arch/x86/kvm/x86.c >>> @@ -5314,6 +5314,10 @@ static void kvm_init_msr_list(void) >>> if (msrs_to_save_all[i] - MSR_ARCH_PERFMON_EVENTSEL0 >= >>> min(INTEL_PMC_MAX_GENERIC, x86_pmu.num_counters_gp)) >>> continue; >>> + break; >>> + case MSR_IA32_UMWAIT_CONTROL: >>> + if (!kvm_cpu_cap_has(X86_FEATURE_WAITPKG)) >>> + continue; >> >> I'm probably missing something but (if I understand correctly) the only >> effect of dropping MSR_IA32_UMWAIT_CONTROL from msrs_to_save would be >> that KVM userspace won't see it in e.g. KVM_GET_MSR_INDEX_LIST. But why >> is this causing an issue? I see both vmx_get_msr()/vmx_set_msr() have >> 'host_initiated' check: >> >> case MSR_IA32_UMWAIT_CONTROL: >> if (!msr_info->host_initiated && !vmx_has_waitpkg(vmx)) >> return 1; > > Here it fails like that: > > 1. KVM_GET_MSR_INDEX_LIST returns this msrs, and qemu notes that > it is supported in 'has_msr_umwait' global var In general, KVM_GET_MSR_INDEX_LIST won't return MSR_IA32_UMWAIT_CONTROL if KVM cannot read this MSR, see kvm_init_msr_list(). You hit issue because you used "ignore_msrs".