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

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Message-ID: <70078abb-f8b7-cd33-5bdd-bc6ee44c0bd3@amd.com>
Date:   Thu, 8 Dec 2022 17:39:44 +0530
From:   Santosh Shukla <santosh.shukla@....com>
To:     Maxim Levitsky <mlevitsk@...hat.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 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.

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);
>>>  	}
>>>  }
>>>  
> 
>