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

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Message-ID: <94f330693be7431fa6d586cc317c26bc@huawei.com>
Date:   Wed, 19 Feb 2020 01:59:09 +0000
From:   linmiaohe <linmiaohe@...wei.com>
To:     Sean Christopherson <sean.j.christopherson@...el.com>
CC:     "pbonzini@...hat.com" <pbonzini@...hat.com>,
        "rkrcmar@...hat.com" <rkrcmar@...hat.com>,
        "vkuznets@...hat.com" <vkuznets@...hat.com>,
        "wanpengli@...cent.com" <wanpengli@...cent.com>,
        "jmattson@...gle.com" <jmattson@...gle.com>,
        "joro@...tes.org" <joro@...tes.org>,
        "tglx@...utronix.de" <tglx@...utronix.de>,
        "mingo@...hat.com" <mingo@...hat.com>,
        "bp@...en8.de" <bp@...en8.de>, "hpa@...or.com" <hpa@...or.com>,
        "kvm@...r.kernel.org" <kvm@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "x86@...nel.org" <x86@...nel.org>
Subject: Re: [PATCH] KVM: VMX: replace "fall through" with "return true" to
 indicate different case

Sean Christopherson <sean.j.christopherson@...el.com> wrote:
>On Tue, Feb 18, 2020 at 11:39:28AM +0800, linmiaohe wrote:
>> From: Miaohe Lin <linmiaohe@...wei.com>
>> 
>> @@ -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.

Yeh, it looks better this way. But from a different perspective, "return turn" here indicates #BP and #DB need do vcpu->guest_debug checks, while others not.
Thanks. :)

>
>>  	case DE_VECTOR:
>>  	case OF_VECTOR:
>>  	case BR_VECTOR: