linux-kernel - Re: [PATCH 3/3] KVM: nVMX: Clear IDT vectoring on nested VM-Exit for double/triple fault

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Date:   Thu, 7 Apr 2022 16:02:07 +0800
From:   Xiaoyao Li <xiaoyao.li@...el.com>
To:     Sean Christopherson <seanjc@...gle.com>,
        Paolo Bonzini <pbonzini@...hat.com>
Cc:     Vitaly Kuznetsov <vkuznets@...hat.com>,
        Wanpeng Li <wanpengli@...cent.com>,
        Jim Mattson <jmattson@...gle.com>,
        Joerg Roedel <joro@...tes.org>, kvm@...r.kernel.org,
        linux-kernel@...r.kernel.org, Chenyi Qiang <chenyi.qiang@...el.com>
Subject: Re: [PATCH 3/3] KVM: nVMX: Clear IDT vectoring on nested VM-Exit for
 double/triple fault

On 4/7/2022 8:23 AM, Sean Christopherson wrote:
> Clear the IDT vectoring field in vmcs12 on next VM-Exit due to a double
> or triple fault.  Per the SDM, a VM-Exit isn't considered to occur during
> event delivery if the exit is due to an intercepted double fault or a
> triple fault.  Opportunistically move the default clearing (no event
> "pending") into the helper so that it's more obvious that KVM does indeed
> handle this case.
> 
> Note, the double fault case is worded rather wierdly in the SDM:
> 
>    The original event results in a double-fault exception that causes the
>    VM exit directly.
> 
> Temporarily ignoring injected events, double faults can _only_ occur if
> an exception occurs while attempting to deliver a different exception,
> i.e. there's _always_ an original event.  And for injected double fault,
> while there's no original event, injected events are never subject to
> interception.
> 
> Presumably the SDM is calling out that a the vectoring info will be valid
> if a different exit occurs after a double fault, e.g. if a #PF occurs and
> is intercepted while vectoring #DF, then the vectoring info will show the
> double fault.  

Wouldn't it be a tripe fault exit in this case?

> In other words, the clause can simply be read as:
> 
>    The VM exit is caused by a double-fault exception.