From mboxrd@z Thu Jan 1 00:00:00 1970 From: Paolo Bonzini Subject: Re: [PATCH] KVM: x86: no need to check CPL for XSETBV on VMX Date: Fri, 15 Apr 2016 12:11:21 +0200 Message-ID: <5710BE49.4000702@redhat.com> References: <57104A23.4070405@gmail.com> Mime-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: 7bit To: Yang Zhang , "kvm@vger.kernel.org" , "rkrcmar@redhat.com" Return-path: Received: from mx1.redhat.com ([209.132.183.28]:33496 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751260AbcDOKLa (ORCPT ); Fri, 15 Apr 2016 06:11:30 -0400 In-Reply-To: <57104A23.4070405@gmail.com> Sender: kvm-owner@vger.kernel.org List-ID: On 15/04/2016 03:55, Yang Zhang wrote: > The CPL check for XSETBV instruction is done by hardware on VMX. > It only needs by SVM. I don't think this is performance-sensitive, hence it's simpler to keep the code as simple as possible. For example, if one added XSETBV support to the emulator, your patch would introduce a bug. Paolo > Signed-off-by: Yang Zhang > --- > arch/x86/kvm/svm.c | 4 +++- > arch/x86/kvm/x86.c | 3 +-- > 2 files changed, 4 insertions(+), 3 deletions(-) > > diff --git a/arch/x86/kvm/svm.c b/arch/x86/kvm/svm.c > index 31346a3..14680f5 100644 > --- a/arch/x86/kvm/svm.c > +++ b/arch/x86/kvm/svm.c > @@ -2715,7 +2715,9 @@ static int xsetbv_interception(struct vcpu_svm *svm) > u64 new_bv = kvm_read_edx_eax(&svm->vcpu); > u32 index = kvm_register_read(&svm->vcpu, VCPU_REGS_RCX); > > - if (kvm_set_xcr(&svm->vcpu, index, new_bv) == 0) { > + if (svm_get_cpl(&svm->vcpu) != 0) > + kvm_inject_gp(&svm->vcpu, 0); > + else if (kvm_set_xcr(&svm->vcpu, index, new_bv) == 0) { > svm->next_rip = kvm_rip_read(&svm->vcpu) + 3; > skip_emulated_instruction(&svm->vcpu); > } > diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c > index 8f57335..3cfc59f 100644 > --- a/arch/x86/kvm/x86.c > +++ b/arch/x86/kvm/x86.c > @@ -709,8 +709,7 @@ static int __kvm_set_xcr(struct kvm_vcpu *vcpu, u32 > index, u64 xcr) > > int kvm_set_xcr(struct kvm_vcpu *vcpu, u32 index, u64 xcr) > { > - if (kvm_x86_ops->get_cpl(vcpu) != 0 || > - __kvm_set_xcr(vcpu, index, xcr)) { > + if (__kvm_set_xcr(vcpu, index, xcr)) { > kvm_inject_gp(vcpu, 0); > return 1; > }