linux-kernel - Re: [PATCHv4 11/11] KVM: nSVM: implement support for nested VNMI

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Date:   Wed, 22 Mar 2023 17:50:50 -0700
From:   Sean Christopherson <seanjc@...gle.com>
To:     Santosh Shukla <santosh.shukla@....com>
Cc:     kvm@...r.kernel.org, pbonzini@...hat.com, jmattson@...gle.com,
        joro@...tes.org, linux-kernel@...r.kernel.org,
        mail@...iej.szmigiero.name, mlevitsk@...hat.com,
        thomas.lendacky@....com, vkuznets@...hat.com
Subject: Re: [PATCHv4 11/11] KVM: nSVM: implement support for nested VNMI

On Mon, Feb 27, 2023, Santosh Shukla wrote:
> Allows L1 to use vNMI to accelerate its injection of NMI
> to L2 by passing through vNMI int_ctl bits from vmcb12
> to/from vmcb02.
> 
> In case of L1 and L2 both using VNMI- Copy VNMI bits from vmcb12 to
> vmcb02 during entry and vice-versa during exit.
> And in case of L1 uses VNMI and L2 doesn't- Copy VNMI bits from vmcb01 to
> vmcb02 during entry and vice-versa during exit.

This changelog is again stale, as it does not match the code.  Or maybe it never
matched the code.  The code looks correct though.

    KVM: nSVM: Implement support for nested VNMI
    
    Allow L1 to use vNMI to accelerate its injection of NMI to L2 by
    propagating vNMI int_ctl bits from/to vmcb12 to/from vmcb02.
    
    To handle both the case where vNMI is enabled for L1 and L2, and where
    vNMI is enabled for L1 but _not_ L2, move pending L1 vNMIs to nmi_pending
    on nested VM-Entry and raise KVM_REQ_EVENT, i.e. rely on existing code to
    route the NMI to the correct domain.
    
    On nested VM-Exit, reverse the process and set/clear V_NMI_PENDING for L1
    based one whether nmi_pending is zero or non-zero.  There is no need to
    consider vmcb02 in this case, as V_NMI_PENDING can be set in vmcb02 if
    vNMI is disabled for L2, and if vNMI is enabled for L2, then L1 and L2
    have different NMI contexts.