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=-2.5 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_PASS,URIBL_BLOCKED,USER_AGENT_MUTT autolearn=ham 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 084B5C43381 for ; Fri, 8 Mar 2019 15:50:53 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id C507D2087C for ; Fri, 8 Mar 2019 15:50:52 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726425AbfCHPuv (ORCPT ); Fri, 8 Mar 2019 10:50:51 -0500 Received: from mga04.intel.com ([192.55.52.120]:17094 "EHLO mga04.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726171AbfCHPuu (ORCPT ); Fri, 8 Mar 2019 10:50:50 -0500 X-Amp-Result: UNKNOWN X-Amp-Original-Verdict: FILE UNKNOWN X-Amp-File-Uploaded: False Received: from fmsmga004.fm.intel.com ([10.253.24.48]) by fmsmga104.fm.intel.com with ESMTP/TLS/DHE-RSA-AES256-GCM-SHA384; 08 Mar 2019 07:50:47 -0800 X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="5.58,456,1544515200"; d="scan'208";a="150528249" Received: from sjchrist-coffee.jf.intel.com (HELO linux.intel.com) ([10.54.74.181]) by fmsmga004.fm.intel.com with ESMTP; 08 Mar 2019 07:50:46 -0800 Date: Fri, 8 Mar 2019 07:50:46 -0800 From: Sean Christopherson To: Paolo Bonzini Cc: Yang Weijiang , rkrcmar@redhat.com, jmattson@google.com, linux-kernel@vger.kernel.org, kvm@vger.kernel.org, mst@redhat.com, yu-cheng.yu@intel.com, yi.z.zhang@intel.com, hjl.tools@gmail.com, Zhang Yi Z Subject: Re: [PATCH v2 1/7] KVM:VMX: Define CET VMCS fields and bits Message-ID: <20190308155046.GA2528@linux.intel.com> References: <20190122205909.24165-1-weijiang.yang@intel.com> <20190122205909.24165-2-weijiang.yang@intel.com> <5a31eef0-2b6c-bdc2-c54b-5dc4cecf084d@redhat.com> <20190128103345.GA29895@local-michael-cet-test.sh.intel.com> <4d9a5393-163b-f32a-4657-cec54093ee88@redhat.com> <20190304185621.GG17120@linux.intel.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.5.24 (2015-08-30) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Fri, Mar 08, 2019 at 10:15:15AM +0100, Paolo Bonzini wrote: > On 04/03/19 19:56, Sean Christopherson wrote: > > On Tue, Jan 29, 2019 at 04:19:34PM +0100, Paolo Bonzini wrote: > >> On 28/01/19 11:33, Yang Weijiang wrote: > >>>> There is no code in this series to pass these fields to and from > >>>> userspace, and also to save/restore U_CET, INT_SSP_TAB, PL0_SSP and > >>>> PL3_SSP across context switches. > >>>> > >>> The kernel consumes these MSRs, please see kernel CET patch: > >>> https://lkml.org/lkml/fancy/2018/11/20/225 > >> > >> Still, even if the kernel saves these fields across context switch in > >> XSAVE areas, KVM must support accesses to the MSRs from userspace, for > >> example in order to perform live migration. > >> > >> For example, when reading/writing these in kvm_set_msr or > >> kvm_get_msr_common, you would have to do a read/write from the host > >> MSRs. You also have to put kvm_load_guest_fpu/kvm_put_guest_fpu calls > >> in __msr_io. > > > > Paolo, can you elaborate on why KVM would read the host MSRs? Wouldn't > > kvm_{get,set}_msr() pull the values from the VMCS when necessary? > > Not all MSRs are in the VMCS; IA32_U_CET and IA32_PL*_SSP are not. Ah, "host MSRs" confused me. I though you meant the host's version of the MSRs, but you're saying do an XRSTORS to load the guest's FPU state and then {RD,WR}MSR to pull the guest's value from hardware.