Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752243AbdLND1e (ORCPT ); Wed, 13 Dec 2017 22:27:34 -0500 Received: from mail-oi0-f65.google.com ([209.85.218.65]:38295 "EHLO mail-oi0-f65.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751092AbdLND1d (ORCPT ); Wed, 13 Dec 2017 22:27:33 -0500 X-Google-Smtp-Source: ACJfBov52jT35up7ZeRIQuDQ/qnuxIxT4n9WSNCOJEzuw3A3NRWZkqYfIHcvEOBw+WKZQw0hNd2k7g== Subject: Re: [PATCH] KVM: x86: avoid unnecessary XSETBV on guest entry To: Paolo Bonzini , linux-kernel@vger.kernel.org, kvm@vger.kernel.org Cc: wanpeng.li@hotmail.com References: <1513169512-28139-1-git-send-email-pbonzini@redhat.com> From: Quan Xu Message-ID: Date: Thu, 14 Dec 2017 11:27:27 +0800 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:52.0) Gecko/20100101 Thunderbird/52.5.0 MIME-Version: 1.0 In-Reply-To: <1513169512-28139-1-git-send-email-pbonzini@redhat.com> Content-Type: text/plain; charset=utf-8; format=flowed Content-Transfer-Encoding: 7bit Content-Language: en-US Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 881 Lines: 27 On 2017/12/13 20:51, 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; > } > } Reviewed-by: Quan Xu