linux-kernel - Re: [PATCH v3] KVM: VMX: Enable Notify VM exit

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Message-ID: <7859e03f-10fa-dbc2-ed3c-5c09e62f9016@redhat.com>
Date:   Fri, 25 Feb 2022 16:13:21 +0100
From:   Paolo Bonzini <pbonzini@...hat.com>
To:     Xiaoyao Li <xiaoyao.li@...el.com>,
        Jim Mattson <jmattson@...gle.com>,
        Chenyi Qiang <chenyi.qiang@...el.com>
Cc:     Sean Christopherson <seanjc@...gle.com>,
        Vitaly Kuznetsov <vkuznets@...hat.com>,
        Wanpeng Li <wanpengli@...cent.com>,
        Joerg Roedel <joro@...tes.org>, kvm@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v3] KVM: VMX: Enable Notify VM exit

On 2/25/22 16:12, Xiaoyao Li wrote:
>>>>
>>>
>>> I don't like the idea of making things up without notifying userspace
>>> that this is fictional. How is my customer running nested VMs supposed
>>> to know that L2 didn't actually shutdown, but L0 killed it because the
>>> notify window was exceeded? If this information isn't reported to
>>> userspace, I have no way of getting the information to the customer.
>>
>> Then, maybe a dedicated software define VM exit for it instead of 
>> reusing triple fault?
>>
> 
> Second thought, we can even just return Notify VM exit to L1 to tell L2 
> causes Notify VM exit, even thought Notify VM exit is not exposed to L1.

That might cause NULL pointer dereferences or other nasty occurrences.

Paolo