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

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Message-ID: <fae3d3ea-4aaa-bf20-46eb-596be712f36a@amd.com>
Date:   Thu, 21 Jul 2022 14:55:50 +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 7/10/2022 9:39 PM, Maxim Levitsky wrote:
> On Fri, 2022-06-17 at 20:18 +0530, Shukla, Santosh wrote:
>>
>> 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.
> 
> And yet, svm_set_nmi_mask is called when KVM wants to explicitly mask NMI
> without injecting a NMI, it does this when entering (emulated) SMI.
> 
> So the KVM has to set V_NMI_MASK here, becaue no real NMI is injected,
> and thus the CPU will not set this bit itself.
> 

Yes, we will handle smm case in v3.

Thanks,
Santosh

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