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

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Message-ID: <06d12050eece922e786b7bee1254698466c6d3d4.camel@redhat.com>
Date:   Thu, 08 Dec 2022 15:44:55 +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 Thu, 2022-12-08 at 17:39 +0530, Santosh Shukla wrote:
> 
> On 12/6/2022 5:44 PM, Maxim Levitsky wrote:
> > 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.
> > 
> I think current approach is fine since function used in svm.c only. but I have
> no strong opinion on moving to svm.h either ways.

I also think so, just noticed something in case there are any objections.

Best regards,
	Maxim Levitsky

> 
> Thanks,
> Santosh
> 
> > 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);
> > > >  	}
> > > >  }
> > > >