Re: [PATCH] KVM: VMX: Enable Notify VM exit

From: Xiaoyao Li <xiaoyao.li@intel.com>
To: Tao Xu <tao3.xu@intel.com>, Andy Lutomirski <luto@amacapital.net>
Cc: Paolo Bonzini <pbonzini@redhat.com>,
	"Christopherson, Sean J" <sean.j.christopherson@intel.com>,
	Vitaly Kuznetsov <vkuznets@redhat.com>,
	Wanpeng Li <wanpengli@tencent.com>,
	Jim Mattson <jmattson@google.com>, Joerg Roedel <joro@8bytes.org>,
	Thomas Gleixner <tglx@linutronix.de>,
	Ingo Molnar <mingo@redhat.com>, Borislav Petkov <bp@alien8.de>,
	"H. Peter Anvin" <hpa@zytor.com>, X86 ML <x86@kernel.org>,
	kvm list <kvm@vger.kernel.org>,
	LKML <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH] KVM: VMX: Enable Notify VM exit
Date: Tue, 3 Nov 2020 15:29:33 +0800	[thread overview]
Message-ID: <a7c8cdeb-c5be-a00f-eb2f-fcc8762c07b2@intel.com> (raw)
In-Reply-To: <a5f500ee-51f8-54a7-d927-0e8eee644e26@intel.com>

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@intel.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.