linux-kernel - Re: [PATCH 4/4] KVM/VMX: Fold handle_interrupt_nmi

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Date:   Sat, 01 May 2021 01:28:14 +0200
From:   Thomas Gleixner <tglx@...utronix.de>
To:     Paolo Bonzini <pbonzini@...hat.com>,
        Lai Jiangshan <jiangshanlai@...il.com>,
        linux-kernel@...r.kernel.org
Cc:     Lai Jiangshan <laijs@...ux.alibaba.com>,
        Sean Christopherson <seanjc@...gle.com>,
        Vitaly Kuznetsov <vkuznets@...hat.com>,
        Wanpeng Li <wanpengli@...cent.com>,
        Jim Mattson <jmattson@...gle.com>,
        Joerg Roedel <joro@...tes.org>, Ingo Molnar <mingo@...hat.com>,
        Borislav Petkov <bp@...en8.de>, x86@...nel.org,
        "H. Peter Anvin" <hpa@...or.com>, kvm@...r.kernel.org
Subject: Re: [PATCH 4/4] KVM/VMX: Fold handle_interrupt_nmi_irqoff() into its solo caller

On Fri, Apr 30 2021 at 11:06, Paolo Bonzini wrote:

> On 30/04/21 11:03, Thomas Gleixner wrote:
>> Lai,
>> 
>> On Tue, Apr 27 2021 at 07:09, Lai Jiangshan wrote:
>>>   	u32 intr_info = vmx_get_intr_info(&vmx->vcpu);
>>> @@ -6427,12 +6417,19 @@ static void handle_exception_nmi_irqoff(struct vcpu_vmx *vmx)
>>>   static void handle_external_interrupt_irqoff(struct kvm_vcpu *vcpu)
>>>   {
>>>   	u32 intr_info = vmx_get_intr_info(vcpu);
>>> +	unsigned int vector;
>>> +	gate_desc *desc;
>>>   
>>>   	if (WARN_ONCE(!is_external_intr(intr_info),
>>>   	    "KVM: unexpected VM-Exit interrupt info: 0x%x", intr_info))
>>>   		return;
>>>   
>>> -	handle_interrupt_nmi_irqoff(vcpu, intr_info);
>>> +	vector = intr_info & INTR_INFO_VECTOR_MASK;
>>> +	desc = (gate_desc *)host_idt_base + vector;
>>> +
>>> +	kvm_before_interrupt(vcpu);
>>> +	vmx_do_interrupt_nmi_irqoff(gate_offset(desc));
>>> +	kvm_after_interrupt(vcpu);
>> 
>> So the previous patch does:
>> 
>> +               kvm_before_interrupt(&vmx->vcpu);
>> +               vmx_do_interrupt_nmi_irqoff((unsigned long)asm_noist_exc_nmi);
>> +               kvm_after_interrupt(&vmx->vcpu);
>> 
>> What is this idt gate descriptor dance for in this code?
>
> NMIs are sent through a different vmexit code (the same one as 
> exceptions).  This one is for interrupts.

Duh. Yes. The ability to read is clearly an advantage...