linux-kernel - Re: [PATCH] KVM: VMX: replace "fall through" with "return true" to indicate different case

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Date:   Tue, 18 Feb 2020 07:42:54 -0800
From:   Sean Christopherson <sean.j.christopherson@...el.com>
To:     linmiaohe <linmiaohe@...wei.com>
Cc:     pbonzini@...hat.com, rkrcmar@...hat.com, vkuznets@...hat.com,
        wanpengli@...cent.com, jmattson@...gle.com, joro@...tes.org,
        tglx@...utronix.de, mingo@...hat.com, bp@...en8.de, hpa@...or.com,
        kvm@...r.kernel.org, linux-kernel@...r.kernel.org, x86@...nel.org
Subject: Re: [PATCH] KVM: VMX: replace "fall through" with "return true" to
 indicate different case

On Tue, Feb 18, 2020 at 11:39:28AM +0800, linmiaohe wrote:
> From: Miaohe Lin <linmiaohe@...wei.com>
> 
> The second "/* fall through */" in rmode_exception() makes code harder to
> read. Replace it with "return true" to indicate they are different cases
> and also this improves the readability.
> 
> Suggested-by: Vitaly Kuznetsov <vkuznets@...hat.com>
> Signed-off-by: Miaohe Lin <linmiaohe@...wei.com>
> ---
>  arch/x86/kvm/vmx/vmx.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/arch/x86/kvm/vmx/vmx.c b/arch/x86/kvm/vmx/vmx.c
> index a13368b2719c..c5bcbbada2db 100644
> --- a/arch/x86/kvm/vmx/vmx.c
> +++ b/arch/x86/kvm/vmx/vmx.c
> @@ -4495,7 +4495,7 @@ static bool rmode_exception(struct kvm_vcpu *vcpu, int vec)
>  		if (vcpu->guest_debug &
>  			(KVM_GUESTDBG_SINGLESTEP | KVM_GUESTDBG_USE_HW_BP))
>  			return false;
> -		/* fall through */
> +		return true;

I prefer the current code, i.e. the fall through.  This code is already
burdened with a fall through, from #BP->#DB, and IMO the fall through makes
it more obvious that the vcpu->guest_debug checks are corner cases, while
everything else is handled by common logic.

>  	case DE_VECTOR:
>  	case OF_VECTOR:
>  	case BR_VECTOR:
> -- 
> 2.19.1
>