linux-kernel - Re: [PATCH] KVM: X86: correct meaningless kvm_apicv

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Date:   Mon, 16 Mar 2020 08:59:11 -0700
From:   Sean Christopherson <sean.j.christopherson@...el.com>
To:     Vitaly Kuznetsov <vkuznets@...hat.com>
Cc:     Paolo Bonzini <pbonzini@...hat.com>, linmiaohe@...wei.com,
        linux-kernel@...r.kernel.org, kvm@...r.kernel.org
Subject: Re: [PATCH] KVM: X86: correct meaningless kvm_apicv_activated() check

On Mon, Mar 16, 2020 at 04:44:47PM +0100, Vitaly Kuznetsov wrote:
> Sean Christopherson <sean.j.christopherson@...el.com> writes:
> 
> > On Mon, Mar 16, 2020 at 09:33:50AM +0100, Vitaly Kuznetsov wrote:
> >> Paolo Bonzini <pbonzini@...hat.com> writes:
> >> > +	if ((old == 0) == (new == 0))
> >> > +		return;
> >> 
> >> This is a very laconic expression I personally find hard to read :-)
> >> 
> >> 	/* Check if WE actually changed APICv state */
> >>         if ((!old && !new) || (old && new))
> >> 		return;
> >> 
> >> would be my preference (not strong though, I read yours several times
> >> and now I feel like I understand it just fine :-)
> >
> > Or maybe this to avoid so many equals signs?
> >
> > 	if (!old == !new)
> > 		return;
> >
> 
> 	if (!!old == !!new)
> 		return;
> 
> to make it clear we're converting them to 1/0 :-)

All I can think of now is the Onion article regarding razor blades...

	if (!!!!old == !!!!new)
		return;