linux-kernel - Re: [PATCHv3 5/8] KVM: SVM: Add VNMI support in inject

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Date:   Thu, 25 Aug 2022 16:26:13 +0530
From:   "Shukla, Santosh" <santosh.shukla@....com>
To:     "Maciej S. Szmigiero" <mail@...iej.szmigiero.name>,
        "Shukla, Santosh" <santosh.shukla@....com>
Cc:     Paolo Bonzini <pbonzini@...hat.com>,
        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, mlevitsk@...hat.com
Subject: Re: [PATCHv3 5/8] KVM: SVM: Add VNMI support in inject_nmi

On 8/24/2022 6:26 PM, Maciej S. Szmigiero wrote:
> On 24.08.2022 14:13, Shukla, Santosh wrote:
>> Hi Maciej,
>>
>> On 8/11/2022 2:54 AM, Maciej S. Szmigiero wrote:
>>> On 10.08.2022 08:12, Santosh Shukla wrote:
>>>> Inject the NMI by setting V_NMI in the VMCB interrupt control. processor
>>>> will clear V_NMI to acknowledge processing has started and will keep the
>>>> V_NMI_MASK set until the processor is done with processing the NMI event.
>>>>
>>>> Signed-off-by: Santosh Shukla <santosh.shukla@....com>
>>>> ---
>>>> v3:
>>>> - Removed WARN_ON check.
>>>>
>>>> v2:
>>>> - Added WARN_ON check for vnmi pending.
>>>> - use `get_vnmi_vmcb` to get correct vmcb so to inject vnmi.
>>>>
>>>>    arch/x86/kvm/svm/svm.c | 7 +++++++
>>>>    1 file changed, 7 insertions(+)
>>>>
>>>> diff --git a/arch/x86/kvm/svm/svm.c b/arch/x86/kvm/svm/svm.c
>>>> index e260e8cb0c81..8c4098b8a63e 100644
>>>> --- a/arch/x86/kvm/svm/svm.c
>>>> +++ b/arch/x86/kvm/svm/svm.c
>>>> @@ -3479,7 +3479,14 @@ static void pre_svm_run(struct kvm_vcpu *vcpu)
>>>>    static void svm_inject_nmi(struct kvm_vcpu *vcpu)
>>>>    {
>>>>        struct vcpu_svm *svm = to_svm(vcpu);
>>>> +    struct vmcb *vmcb = NULL;
>>>>    +    if (is_vnmi_enabled(svm)) {
>>>
>>> I guess this should be "is_vnmi_enabled(svm) && !svm->nmi_l1_to_l2"
>>> since if nmi_l1_to_l2 is true then the NMI to be injected originally
>>> comes from L1's VMCB12 EVENTINJ field.
>>>
>>
>> Not sure if I understood the case fully.. so trying to sketch scenario here -
>> if nmi_l1_to_l2 is true then event is coming from EVTINJ. .which could
>> be one of following case -
>> 1) L0 (vnmi enabled) and L1 (vnmi disabled)
> 
> As far as I can see in this case:
> is_vnmi_enabled() returns whether VMCB02's int_ctl has V_NMI_ENABLE bit set.
> 

For L1 with vnmi disabled case - is_vnmi_enabled()->get_vnmi_vmcb() will return false so the
execution path will opt EVTINJ model for re-injection.

Thanks,
Santosh

> This field in VMCB02 comes from nested_vmcb02_prepare_control() which
> in the !nested_vnmi_enabled() case (L1 is not using vNMI) copies these bits
> from VMCB01:
>> int_ctl_vmcb01_bits |= (V_NMI_PENDING | V_NMI_ENABLE | V_NMI_MASK);
> 
> So in this case (L0 uses vNMI) V_NMI_ENABLE will be set in VMCB01, right?
> 
> This bit will then be copied to VMCB02 so re-injection will attempt to use
> vNMI instead of EVTINJ.
> 
>> 2) L0 & L1 both vnmi disabled.
> 
> This case is ok.
> 
>>
>> In both cases the vnmi check will fail for L1 and execution path
>> will fall back to default - right?
>>
>> Thanks,
>> Santosh
> 
> Thanks,
> Maciej