Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753829AbdLMTDg (ORCPT ); Wed, 13 Dec 2017 14:03:36 -0500 Received: from mail-it0-f68.google.com ([209.85.214.68]:45691 "EHLO mail-it0-f68.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753106AbdLMTDe (ORCPT ); Wed, 13 Dec 2017 14:03:34 -0500 X-Google-Smtp-Source: ACJfBovQFJ7rwKg/lFUH2wxQoyMSewNLNfGFCN5MZyoNydyG0P3IPiQyNP5r5m3HnRCBVana0aLodDvPjiFLwJBEBgk= MIME-Version: 1.0 In-Reply-To: <1513169512-28139-1-git-send-email-pbonzini@redhat.com> References: <1513169512-28139-1-git-send-email-pbonzini@redhat.com> From: Jim Mattson Date: Wed, 13 Dec 2017 11:03:31 -0800 Message-ID: Subject: Re: [PATCH] KVM: x86: avoid unnecessary XSETBV on guest entry To: Paolo Bonzini Cc: LKML , kvm list , Wanpeng Li Content-Type: text/plain; charset="UTF-8" Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1031 Lines: 28 Reviewed-by: Jim Mattson On Wed, Dec 13, 2017 at 4:51 AM, Paolo Bonzini wrote: > xsetbv can be expensive when running on nested virtualization, try to > avoid it. > > Signed-off-by: Paolo Bonzini > --- > arch/x86/kvm/x86.c | 3 ++- > 1 file changed, 2 insertions(+), 1 deletion(-) > > diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c > index 0f82e2cbf64c..daa1918031df 100644 > --- a/arch/x86/kvm/x86.c > +++ b/arch/x86/kvm/x86.c > @@ -702,7 +702,8 @@ static void kvm_load_guest_xcr0(struct kvm_vcpu *vcpu) > if (kvm_read_cr4_bits(vcpu, X86_CR4_OSXSAVE) && > !vcpu->guest_xcr0_loaded) { > /* kvm_set_xcr() also depends on this */ > - xsetbv(XCR_XFEATURE_ENABLED_MASK, vcpu->arch.xcr0); > + if (vcpu->arch.xcr0 != host_xcr0) > + xsetbv(XCR_XFEATURE_ENABLED_MASK, vcpu->arch.xcr0); > vcpu->guest_xcr0_loaded = 1; > } > } > -- > 1.8.3.1 >