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

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Message-ID: <6a839b88-392d-886d-836d-ca04cf700dce@intel.com>
Date:   Fri, 25 Feb 2022 23:12:12 +0800
From:   Xiaoyao Li <xiaoyao.li@...el.com>
To:     Jim Mattson <jmattson@...gle.com>,
        Chenyi Qiang <chenyi.qiang@...el.com>
Cc:     Paolo Bonzini <pbonzini@...hat.com>,
        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 2/25/2022 11:04 PM, Xiaoyao Li wrote:
> On 2/25/2022 10:54 PM, Jim Mattson wrote:
>> On Tue, Feb 22, 2022 at 10:19 PM Chenyi Qiang <chenyi.qiang@...el.com> 
>> wrote:
>>> Nested handling
>>> - Nested notify VM exits are not supported yet. Keep the same notify
>>>    window control in vmcs02 as vmcs01, so that L1 can't escape the
>>>    restriction of notify VM exits through launching L2 VM.
>>> - When L2 VM is context invalid, synthesize a nested
>>>    EXIT_REASON_TRIPLE_FAULT to L1 so that L1 won't be killed due to L2's
>>>    VM_CONTEXT_INVALID happens.
>>
>> 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.