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

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Date:   Fri, 17 Jun 2022 20:18:27 +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 6/17/2022 8:15 PM, Shukla, Santosh wrote:
> 
> 
> 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?
>>

V_NMI_MASK is cpu controlled meaning HW sets the mask while processing
event and clears right after processing, so in away its Read-only for hypervisor.

>> Best regards,
>> 	Maxim Levitsky
>>
>>
>>> +
>>>         if (masked) {
>>>                 vcpu->arch.hflags |= HF_NMI_MASK;
>>>                 if (!sev_es_guest(vcpu->kvm))
>>
>>