linux-kernel - Re: [PATCH 3/7] KVM: SVM: Add VNMI support in get/set_nmi

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Message-ID: <91c551a2-11fc-202f-2a8f-75b6374286b6@amd.com>
Date:   Fri, 17 Jun 2022 20:15:00 +0530
From:   "Shukla, Santosh" <santosh.shukla@....com>
To:     Maxim Levitsky <mlevitsk@...hat.com>,
        Paolo Bonzini <pbonzini@...hat.com>
Cc:     Sean Christopherson <seanjc@...gle.com>,
        Vitaly Kuznetsov <vkuznets@...hat.com>,
        Jim Mattson <jmattson@...gle.com>,
        Joerg Roedel <joro@...tes.org>,
        Tom Lendacky <thomas.lendacky@....com>, kvm@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH 3/7] KVM: SVM: Add VNMI support in get/set_nmi_mask



On 6/7/2022 6:37 PM, Maxim Levitsky wrote:
> On Thu, 2022-06-02 at 19:56 +0530, Santosh Shukla wrote:
>> VMCB intr_ctrl bit12 (V_NMI_MASK) is set by the processor when handling
>> NMI in guest and is cleared after the NMI is handled. Treat V_NMI_MASK as
>> read-only in the hypervisor and do not populate set accessors.
>>
>> Signed-off-by: Santosh Shukla <santosh.shukla@....com>
>> ---
>>  arch/x86/kvm/svm/svm.c | 20 +++++++++++++++++++-
>>  1 file changed, 19 insertions(+), 1 deletion(-)
>>
>> diff --git a/arch/x86/kvm/svm/svm.c b/arch/x86/kvm/svm/svm.c
>> index 860f28c668bd..d67a54517d95 100644
>> --- a/arch/x86/kvm/svm/svm.c
>> +++ b/arch/x86/kvm/svm/svm.c
>> @@ -323,6 +323,16 @@ static int is_external_interrupt(u32 info)
>>         return info == (SVM_EVTINJ_VALID | SVM_EVTINJ_TYPE_INTR);
>>  }
>>  
>> +static bool is_vnmi_enabled(struct vmcb *vmcb)
>> +{
>> +       return vnmi && (vmcb->control.int_ctl & V_NMI_ENABLE);
>> +}
> 
> Following Paolo's suggestion I recently removed vgif_enabled(),
> based on the logic that vgif_enabled == vgif, because
> we always enable vGIF for L1 as long as 'vgif' module param is set,
> which is set unless either hardware or user cleared it.
> 
Yes. In v2, Thanks!.

> Note that here vmcb is the current vmcb, which can be vmcb02,
> and it might be wrong
> 
>> +
>> +static bool is_vnmi_mask_set(struct vmcb *vmcb)
>> +{
>> +       return !!(vmcb->control.int_ctl & V_NMI_MASK);
>> +}
>> +
>>  static u32 svm_get_interrupt_shadow(struct kvm_vcpu *vcpu)
>>  {
>>         struct vcpu_svm *svm = to_svm(vcpu);
>> @@ -3502,13 +3512,21 @@ static int svm_nmi_allowed(struct kvm_vcpu *vcpu, bool for_injection)
>>  
>>  static bool svm_get_nmi_mask(struct kvm_vcpu *vcpu)
>>  {
>> -       return !!(vcpu->arch.hflags & HF_NMI_MASK);
>> +       struct vcpu_svm *svm = to_svm(vcpu);
>> +
>> +       if (is_vnmi_enabled(svm->vmcb))
>> +               return is_vnmi_mask_set(svm->vmcb);
>> +       else
>> +               return !!(vcpu->arch.hflags & HF_NMI_MASK);
>>  }
>>  
>>  static void svm_set_nmi_mask(struct kvm_vcpu *vcpu, bool masked)
>>  {
>>         struct vcpu_svm *svm = to_svm(vcpu);
>>  
>> +       if (is_vnmi_enabled(svm->vmcb))
>> +               return;
> 
> What if the KVM wants to mask NMI, shoudn't we update the 
> V_NMI_MASK value in int_ctl instead of doing nothing?
> 
> Best regards,
> 	Maxim Levitsky
> 
> 
>> +
>>         if (masked) {
>>                 vcpu->arch.hflags |= HF_NMI_MASK;
>>                 if (!sev_es_guest(vcpu->kvm))
> 
>