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From:   "Wang, Wei W" <wei.w.wang@intel.com>
To:     "Gonglei (Arei)" <arei.gonglei@huawei.com>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
        "kvm@vger.kernel.org" <kvm@vger.kernel.org>,
        "pbonzini@redhat.com" <pbonzini@redhat.com>,
        "ak@linux.intel.com" <ak@linux.intel.com>
CC:     "Liang, Kan" <kan.liang@intel.com>,
        "peterz@infradead.org" <peterz@infradead.org>,
        "mingo@redhat.com" <mingo@redhat.com>,
        "rkrcmar@redhat.com" <rkrcmar@redhat.com>,
        "Xu, Like" <like.xu@intel.com>,
        "jannh@google.com" <jannh@google.com>
Subject: RE: [PATCH v3 5/5] KVM/x86/lbr: lazy save the guest lbr stack
Thread-Topic: [PATCH v3 5/5] KVM/x86/lbr: lazy save the guest lbr stack
Thread-Index: AQHUUM3r0paOOfw3cUyiMvfFvyNRYKT4jVyAgAuiBxA=
Date:   Thu, 27 Sep 2018 14:11:08 +0000
Message-ID: <286AC319A985734F985F78AFA26841F7397FD491@shsmsx102.ccr.corp.intel.com>
References: <1537437959-8751-1-git-send-email-wei.w.wang@intel.com>
 <1537437959-8751-6-git-send-email-wei.w.wang@intel.com>
 <33183CC9F5247A488A2544077AF19020DB0F7483@dggeml511-mbx.china.huawei.com>
In-Reply-To: <33183CC9F5247A488A2544077AF19020DB0F7483@dggeml511-mbx.china.huawei.com>
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On Thursday, September 20, 2018 8:08 PM, Gonglei (Arei) wrote:
> > +static bool guest_access_lbr_msr(struct kvm_vcpu *vcpu,
> > +				 struct msr_data *msr_info,
> > +				 bool set)
> > +{
> > +	bool ret = false;
> > +
> > +	if (!vcpu->kvm->arch.guest_lbr_enabled)
> > +		return false;
> > +
> > +	if (set)
> > +		ret = guest_set_lbr_msr(vcpu, msr_info);
> > +	else
> > +		ret = guest_get_lbr_msr(vcpu, msr_info);
> > +
> > +	if (ret) {
> > +		vcpu->arch.lbr_used = true;
> > +		vmx_set_intercept_for_lbr_msrs(vcpu, false);
> 
> You can use if (!vcpu->arch.lbr_used) as the condition of assign values.
> They are need only once.

Thanks, I think it would be better to use

If (ret && !vcpu->arch.lbr_used)
(we need to make sure that the guest is accessing one of the LBR related MSRs via ret=true)

Best,
Wei