From mboxrd@z Thu Jan 1 00:00:00 1970 From: Sean Christopherson Subject: Re: [PATCH v2 1/7] KVM:VMX: Define CET VMCS fields and bits Date: Mon, 4 Mar 2019 10:56:21 -0800 Message-ID: <20190304185621.GG17120@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> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii 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 To: Paolo Bonzini Return-path: Content-Disposition: inline In-Reply-To: <4d9a5393-163b-f32a-4657-cec54093ee88@redhat.com> Sender: linux-kernel-owner@vger.kernel.org List-Id: kvm.vger.kernel.org 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?