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 8BE11C433E0 for ; Thu, 21 May 2020 04:33:36 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 6F29F2078B for ; Thu, 21 May 2020 04:33:36 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727881AbgEUEdd (ORCPT ); Thu, 21 May 2020 00:33:33 -0400 Received: from mga17.intel.com ([192.55.52.151]:50461 "EHLO mga17.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726887AbgEUEdd (ORCPT ); Thu, 21 May 2020 00:33:33 -0400 IronPort-SDR: fA+nWxifwI6RKjL7alkgoIhH/qX/51BsSmbK8r9NEQwVQZKx2PYOS7y0+Gn/uP3xKldsws8MnS eq+2ryjpd1oA== X-Amp-Result: SKIPPED(no attachment in message) X-Amp-File-Uploaded: False Received: from orsmga005.jf.intel.com ([10.7.209.41]) by fmsmga107.fm.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 20 May 2020 21:33:32 -0700 IronPort-SDR: CT43a8HatG1xkf9qNaC/adIJD2PMhXHnATR8T0/7G9SttpLbTkKgBVtgNqgQ76EDaFCGpUwbrv 0vSwoiNt6+Eg== X-IronPort-AV: E=Sophos;i="5.73,416,1583222400"; d="scan'208";a="440300490" 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; 20 May 2020 21:33:31 -0700 Subject: Re: [PATCH 2/2] kvm/x86: don't expose MSR_IA32_UMWAIT_CONTROL unconditionally To: Paolo Bonzini , Maxim Levitsky , kvm@vger.kernel.org, Tao Xu Cc: linux-kernel@vger.kernel.org References: <20200520160740.6144-1-mlevitsk@redhat.com> <20200520160740.6144-3-mlevitsk@redhat.com> From: Xiaoyao Li Message-ID: <81228a0e-7797-4f34-3d6d-5b0550c10a8f@intel.com> Date: Thu, 21 May 2020 12:33:29 +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: 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 5:05 AM, Paolo Bonzini wrote: > On 20/05/20 18:07, Maxim Levitsky wrote: >> 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; >> default: >> break; >> } > > The patch is correct, and matches what is done for the other entries of > msrs_to_save_all. However, while looking at it I noticed that > X86_FEATURE_WAITPKG is actually never added, and that is because it was > also not added to the supported CPUID in commit e69e72faa3a0 ("KVM: x86: > Add support for user wait instructions", 2019-09-24), which was before > the kvm_cpu_cap mechanism was added. > > So while at it you should also fix that. The right way to do that is to > add a > > if (vmx_waitpkg_supported()) > kvm_cpu_cap_check_and_set(X86_FEATURE_WAITPKG); + Tao I remember there is certainly some reason why we don't expose WAITPKG to guest by default. Tao, please help clarify it. Thanks, -Xiaoyao > > in vmx_set_cpu_caps. > > Thanks, > > Paolo >