linux-kernel - RE: [PATCH v3 5/5] KVM/x86/lbr: lazy save the guest lbr stack

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Date:   Thu, 27 Sep 2018 14:11:08 +0000
From:   "Wang, Wei W" <wei.w.wang@...el.com>
To:     "Gonglei (Arei)" <arei.gonglei@...wei.com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "kvm@...r.kernel.org" <kvm@...r.kernel.org>,
        "pbonzini@...hat.com" <pbonzini@...hat.com>,
        "ak@...ux.intel.com" <ak@...ux.intel.com>
CC:     "Liang, Kan" <kan.liang@...el.com>,
        "peterz@...radead.org" <peterz@...radead.org>,
        "mingo@...hat.com" <mingo@...hat.com>,
        "rkrcmar@...hat.com" <rkrcmar@...hat.com>,
        "Xu, Like" <like.xu@...el.com>,
        "jannh@...gle.com" <jannh@...gle.com>
Subject: RE: [PATCH v3 5/5] KVM/x86/lbr: lazy save the guest lbr stack

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