linux-kernel - Re: [PATCH] KVM: VMX: Add 'else' to split mutually exclusive case

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Date:   Mon, 17 Feb 2020 10:34:34 +0100
From:   Vitaly Kuznetsov <vkuznets@...hat.com>
To:     linmiaohe <linmiaohe@...wei.com>
Cc:     kvm@...r.kernel.org, linux-kernel@...r.kernel.org, x86@...nel.org,
        pbonzini@...hat.com, rkrcmar@...hat.com,
        sean.j.christopherson@...el.com, wanpengli@...cent.com,
        jmattson@...gle.com, joro@...tes.org, tglx@...utronix.de,
        mingo@...hat.com, bp@...en8.de, hpa@...or.com
Subject: Re: [PATCH] KVM: VMX: Add 'else' to split mutually exclusive case

linmiaohe <linmiaohe@...wei.com> writes:

> From: Miaohe Lin <linmiaohe@...wei.com>
>
> Each if branch in handle_external_interrupt_irqoff() is mutually
> exclusive. Add 'else' to make it clear and also avoid some unnecessary
> check.
>
> Signed-off-by: Miaohe Lin <linmiaohe@...wei.com>
> ---
>  arch/x86/kvm/vmx/vmx.c | 6 ++----
>  1 file changed, 2 insertions(+), 4 deletions(-)
>
> diff --git a/arch/x86/kvm/vmx/vmx.c b/arch/x86/kvm/vmx/vmx.c
> index 9a6664886f2e..bb5c33440af8 100644
> --- a/arch/x86/kvm/vmx/vmx.c
> +++ b/arch/x86/kvm/vmx/vmx.c
> @@ -6178,13 +6178,11 @@ static void handle_exception_nmi_irqoff(struct vcpu_vmx *vmx)
>  	/* if exit due to PF check for async PF */
>  	if (is_page_fault(vmx->exit_intr_info))
>  		vmx->vcpu.arch.apf.host_apf_reason = kvm_read_and_reset_pf_reason();
> -
>  	/* Handle machine checks before interrupts are enabled */
> -	if (is_machine_check(vmx->exit_intr_info))
> +	else if (is_machine_check(vmx->exit_intr_info))
>  		kvm_machine_check();
> -
>  	/* We need to handle NMIs before interrupts are enabled */
> -	if (is_nmi(vmx->exit_intr_info)) {
> +	else if (is_nmi(vmx->exit_intr_info)) {

We'll need to add braces to all branches of the statement,

    if (is_page_fault(vmx->exit_intr_info)) {

    } else if (is_machine_check(vmx->exit_intr_info)) {

    } else if (is_nmi(vmx->exit_intr_info)) {

    }

then.

>  		kvm_before_interrupt(&vmx->vcpu);
>  		asm("int $2");
>  		kvm_after_interrupt(&vmx->vcpu);

-- 
Vitaly