linux-kernel - Re: [PATCH v2 06/11] KVM: SVM: add wrappers to enable/disable IRET interception

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Message-ID: <181f437164296e19683f086c11bf64c11a3f380e.camel@redhat.com>
Date:   Tue, 06 Dec 2022 14:14:23 +0200
From:   Maxim Levitsky <mlevitsk@...hat.com>
To:     Santosh Shukla <santosh.shukla@....com>, kvm@...r.kernel.org
Cc:     Sandipan Das <sandipan.das@....com>,
        Paolo Bonzini <pbonzini@...hat.com>,
        Jim Mattson <jmattson@...gle.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        Borislav Petkov <bp@...en8.de>,
        Pawan Gupta <pawan.kumar.gupta@...ux.intel.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>,
        Josh Poimboeuf <jpoimboe@...nel.org>,
        Daniel Sneddon <daniel.sneddon@...ux.intel.com>,
        Jiaxi Chen <jiaxi.chen@...ux.intel.com>,
        Babu Moger <babu.moger@....com>, linux-kernel@...r.kernel.org,
        Jing Liu <jing2.liu@...el.com>,
        Wyes Karny <wyes.karny@....com>, x86@...nel.org,
        "H. Peter Anvin" <hpa@...or.com>,
        Sean Christopherson <seanjc@...gle.com>
Subject: Re: [PATCH v2 06/11] KVM: SVM: add wrappers to enable/disable IRET
 interception

On Mon, 2022-12-05 at 21:11 +0530, Santosh Shukla wrote:
> On 11/30/2022 1:07 AM, Maxim Levitsky wrote:
> > SEV-ES guests don't use IRET interception for the detection of
> > an end of a NMI.
> > 
> > Therefore it makes sense to create a wrapper to avoid repeating
> > the check for the SEV-ES.
> > 
> > No functional change is intended.
> > 
> > Suggested-by: Sean Christopherson <seanjc@...gle.com>
> > Signed-off-by: Maxim Levitsky <mlevitsk@...hat.com>
> > ---
> >  arch/x86/kvm/svm/svm.c | 28 +++++++++++++++++++---------
> >  1 file changed, 19 insertions(+), 9 deletions(-)
> > 
> > diff --git a/arch/x86/kvm/svm/svm.c b/arch/x86/kvm/svm/svm.c
> > index 512b2aa21137e2..cfed6ab29c839a 100644
> > --- a/arch/x86/kvm/svm/svm.c
> > +++ b/arch/x86/kvm/svm/svm.c
> > @@ -2468,16 +2468,29 @@ static int task_switch_interception(struct kvm_vcpu *vcpu)
> >  			       has_error_code, error_code);
> >  }
> >  
> > +static void svm_disable_iret_interception(struct vcpu_svm *svm)
> > +{
> > +	if (!sev_es_guest(svm->vcpu.kvm))
> > +		svm_clr_intercept(svm, INTERCEPT_IRET);
> > +}
> > +
> > +static void svm_enable_iret_interception(struct vcpu_svm *svm)
> > +{
> > +	if (!sev_es_guest(svm->vcpu.kvm))
> > +		svm_set_intercept(svm, INTERCEPT_IRET);
> > +}
> > +
> 
> nits:
> s/_iret_interception / _iret_intercept
> does that make sense?

Makes sense. I can also move this to svm.h near the svm_set_intercept(), I think
it better a better place for this function there if no objections.

Best regards,
	Maxim Levitsky
> 
> Thanks,
> Santosh
> 
> >  static int iret_interception(struct kvm_vcpu *vcpu)
> >  {
> >  	struct vcpu_svm *svm = to_svm(vcpu);
> >  
> >  	++vcpu->stat.nmi_window_exits;
> >  	svm->awaiting_iret_completion = true;
> > -	if (!sev_es_guest(vcpu->kvm)) {
> > -		svm_clr_intercept(svm, INTERCEPT_IRET);
> > +
> > +	svm_disable_iret_interception(svm);
> > +	if (!sev_es_guest(vcpu->kvm))
> >  		svm->nmi_iret_rip = kvm_rip_read(vcpu);
> > -	}
> > +
> >  	kvm_make_request(KVM_REQ_EVENT, vcpu);
> >  	return 1;
> >  }
> > @@ -3470,8 +3483,7 @@ static void svm_inject_nmi(struct kvm_vcpu *vcpu)
> >  		return;
> >  
> >  	svm->nmi_masked = true;
> > -	if (!sev_es_guest(vcpu->kvm))
> > -		svm_set_intercept(svm, INTERCEPT_IRET);
> > +	svm_enable_iret_interception(svm);
> >  	++vcpu->stat.nmi_injections;
> >  }
> >  
> > @@ -3614,12 +3626,10 @@ static void svm_set_nmi_mask(struct kvm_vcpu *vcpu, bool masked)
> >  
> >  	if (masked) {
> >  		svm->nmi_masked = true;
> > -		if (!sev_es_guest(vcpu->kvm))
> > -			svm_set_intercept(svm, INTERCEPT_IRET);
> > +		svm_enable_iret_interception(svm);
> >  	} else {
> >  		svm->nmi_masked = false;
> > -		if (!sev_es_guest(vcpu->kvm))
> > -			svm_clr_intercept(svm, INTERCEPT_IRET);
> > +		svm_disable_iret_interception(svm);
> >  	}
> >  }
> >