linux-kernel - Re: [PATCHv2 5/7] KVM: SVM: Add VNMI support in inject

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Date:   Fri, 29 Jul 2022 13:53:09 +0000
From:   Sean Christopherson <seanjc@...gle.com>
To:     "Shukla, Santosh" <santosh.shukla@....com>
Cc:     Paolo Bonzini <pbonzini@...hat.com>,
        Vitaly Kuznetsov <vkuznets@...hat.com>,
        Jim Mattson <jmattson@...gle.com>,
        Joerg Roedel <joro@...tes.org>,
        Maxim Levitsky <mlevitsk@...hat.com>,
        Tom Lendacky <thomas.lendacky@....com>, kvm@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCHv2 5/7] KVM: SVM: Add VNMI support in inject_nmi

On Fri, Jul 29, 2022, Shukla, Santosh wrote:
> Hi Sean,
> 
> On 7/21/2022 3:11 AM, Sean Christopherson wrote:
> > On Sat, Jul 09, 2022, Santosh Shukla wrote:
> >> +	++vcpu->stat.nmi_injections;
> >> +	if (is_vnmi_enabled(svm)) {
> >> +		vmcb = get_vnmi_vmcb(svm);
> >> +		WARN_ON(vmcb->control.int_ctl & V_NMI_PENDING);
> > 
> > Haven't read the spec, but based on the changelog I assume the flag doesn't get
> > cleared until the NMI is fully delivered.  That means this WARN will fire if a
> > VM-Exit occurs during delivery as KVM will re-inject the event, e.g. if KVM is
> > using shadow paging and a #PF handle by KVM occurs during delivery.
> > 
> 
> Right,.
> 
> 
> For the above scenario i.e.. if VMEXIT happens during delivery of virtual NMI
> then EXITINTINFO will be set accordingly and V_NMI_MASK is saved as 0.
> hypervisor will re-inject event in next VMRUN.
> 
> I just wanted to track above scenario,. I will replace it with pr_debug().

No, this is normal (albeit uncommon) behavior, don't print anything.  Even if it
weren't normal behavior, pr_debug() is usually the wrong choice in KVM.