Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1030512AbcDMJru (ORCPT ); Wed, 13 Apr 2016 05:47:50 -0400 Received: from mail-pa0-f66.google.com ([209.85.220.66]:33115 "EHLO mail-pa0-f66.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S965968AbcDMJrq (ORCPT ); Wed, 13 Apr 2016 05:47:46 -0400 Subject: Re: [PATCH 1/2] KVM: x86: disable MPX if host did not enable MPX XSAVE features To: Paolo Bonzini References: <1457437481-65784-1-git-send-email-pbonzini@redhat.com> <1457437481-65784-2-git-send-email-pbonzini@redhat.com> <56E2B58B.8020605@redhat.com> <56F3E653.6040901@gmail.com> <56F3E6AB.5070902@redhat.com> Cc: linux-kernel@vger.kernel.org, kvm@vger.kernel.org, Xiao Guangrong From: Yang Zhang Message-ID: <570E15B9.5070205@gmail.com> Date: Wed, 13 Apr 2016 17:47:37 +0800 User-Agent: Mozilla/5.0 (Windows NT 6.1; WOW64; rv:38.0) Gecko/20100101 Thunderbird/38.7.2 MIME-Version: 1.0 In-Reply-To: <56F3E6AB.5070902@redhat.com> Content-Type: text/plain; charset=utf-8; format=flowed Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1636 Lines: 56 On 2016/3/24 21:07, Paolo Bonzini wrote: > > > On 24/03/2016 14:06, Yang Zhang wrote: >> >> I mean why not keep the old way that only activate the eager_fpu while >> guest sees the MPX bit in CPUID, like: >> >> vcpu->arch.eager_fpu = use_eager_fpu() && guest_cpuid_has_mpx(vcpu); > > If the host uses eager FPU you can assume that it's faster than lazy FPU. > > Paolo > >> Besides, vmx_fpu_activate is called when do vcpu_reset. So it seems no >> need to call fpu_activate() here again. Hi Paolo The check in kvm_update_cpuid of fpu is strange since nothing relies on cpuid now. How about the following change? diff --git a/arch/x86/kvm/cpuid.c b/arch/x86/kvm/cpuid.c index bbbaa80..da4e6ad 100644 --- a/arch/x86/kvm/cpuid.c +++ b/arch/x86/kvm/cpuid.c @@ -114,9 +114,6 @@ int kvm_update_cpuid(struct kvm_vcpu *vcpu) if (best && (best->eax & (F(XSAVES) | F(XSAVEC)))) best->ebx = xstate_required_size(vcpu->arch.xcr0, true); - if (use_eager_fpu()) - kvm_x86_ops->fpu_activate(vcpu); - /* * The existing code assumes virtual address is 48-bit in the canonical * address checks; exit if it is ever changed. diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c index 9b7798c..8f57335 100644 --- a/arch/x86/kvm/x86.c +++ b/arch/x86/kvm/x86.c @@ -7453,6 +7453,9 @@ void kvm_vcpu_reset(struct kvm_vcpu *vcpu, bool init_event) vcpu->arch.regs_avail = ~0; vcpu->arch.regs_dirty = ~0; + if (use_eager_fpu()) + kvm_x86_ops->fpu_activate(vcpu); + kvm_x86_ops->vcpu_reset(vcpu, init_event); } -- best regards yang