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

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Message-ID: <a7c8cdeb-c5be-a00f-eb2f-fcc8762c07b2@intel.com>
Date:   Tue, 3 Nov 2020 15:29:33 +0800
From:   Xiaoyao Li <xiaoyao.li@...el.com>
To:     Tao Xu <tao3.xu@...el.com>, Andy Lutomirski <luto@...capital.net>
Cc:     Paolo Bonzini <pbonzini@...hat.com>,
        "Christopherson, Sean J" <sean.j.christopherson@...el.com>,
        Vitaly Kuznetsov <vkuznets@...hat.com>,
        Wanpeng Li <wanpengli@...cent.com>,
        Jim Mattson <jmattson@...gle.com>,
        Joerg Roedel <joro@...tes.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        "H. Peter Anvin" <hpa@...or.com>, X86 ML <x86@...nel.org>,
        kvm list <kvm@...r.kernel.org>,
        LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] KVM: VMX: Enable Notify VM exit

On 11/3/2020 2:08 PM, Tao Xu wrote:
> 
> 
> On 11/3/20 12:43 AM, Andy Lutomirski wrote:
>> On Sun, Nov 1, 2020 at 10:14 PM Tao Xu <tao3.xu@...el.com> wrote:
>>>
...
>>
>>> +static int handle_notify(struct kvm_vcpu *vcpu)
>>> +{
>>> +       unsigned long exit_qualification = 
>>> vmcs_readl(EXIT_QUALIFICATION);
>>> +
>>> +       /*
>>> +        * Notify VM exit happened while executing iret from NMI,
>>> +        * "blocked by NMI" bit has to be set before next VM entry.
>>> +        */
>>> +       if (exit_qualification & NOTIFY_VM_CONTEXT_VALID) {
>>> +               if (enable_vnmi &&
>>> +                   (exit_qualification & INTR_INFO_UNBLOCK_NMI))
>>> +                       vmcs_set_bits(GUEST_INTERRUPTIBILITY_INFO,
>>> +                                     GUEST_INTR_STATE_NMI);
>>
>> This needs actual documentation in the SDM or at least ISE please.
>>

Hi Andy,

Do you mean SDM or ISE should call out it needs to restore "blocked by 
NMI" if bit 12 of exit qualification is set and VMM decides to re-enter 
the guest?

you can refer to SDM 27.2.3 "Information about NMI unblocking Due to 
IRET" in latest SDM 325462-072US

> Notify VM-Exit is defined in ISE, chapter 9.2:
> https://software.intel.com/content/dam/develop/external/us/en/documents/architecture-instruction-set-extensions-programming-reference.pdf 
> 
> 
> I will add this information into commit message. Thank you for reminding 
> me.