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Subject: Re: [PATCH 4/4] KVM/VMX: Fold handle_interrupt_nmi_irqoff() into its
 solo caller
To:     Thomas Gleixner <tglx@linutronix.de>,
        Lai Jiangshan <jiangshanlai@gmail.com>,
        linux-kernel@vger.kernel.org
Cc:     Lai Jiangshan <laijs@linux.alibaba.com>,
        Sean Christopherson <seanjc@google.com>,
        Vitaly Kuznetsov <vkuznets@redhat.com>,
        Wanpeng Li <wanpengli@tencent.com>,
        Jim Mattson <jmattson@google.com>,
        Joerg Roedel <joro@8bytes.org>, Ingo Molnar <mingo@redhat.com>,
        Borislav Petkov <bp@alien8.de>, x86@kernel.org,
        "H. Peter Anvin" <hpa@zytor.com>, kvm@vger.kernel.org
References: <20210426230949.3561-1-jiangshanlai@gmail.com>
 <20210426230949.3561-5-jiangshanlai@gmail.com>
 <87y2d0du02.ffs@nanos.tec.linutronix.de>
From:   Paolo Bonzini <pbonzini@redhat.com>
Message-ID: <ba3f6230-8766-92e5-1189-a114c236fd48@redhat.com>
Date:   Fri, 30 Apr 2021 11:06:32 +0200
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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.

Paolo