linux-kernel - Re: [PATCH 5/8] KVM: x86: use MDA for interrupt matching

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Date:	Fri, 30 Jan 2015 14:09:41 +0100
From:	Radim Krčmář <rkrcmar@...hat.com>
To:	Paolo Bonzini <pbonzini@...hat.com>
Cc:	linux-kernel@...r.kernel.org, kvm@...r.kernel.org,
	Nadav Amit <namit@...technion.ac.il>,
	Gleb Natapov <gleb@...nel.org>
Subject: Re: [PATCH 5/8] KVM: x86: use MDA for interrupt matching

2015-01-30 10:03+0100, Paolo Bonzini:
> On 29/01/2015 22:48, Radim Krčmář wrote:
> > +/* KVM APIC implementation has two quirks
> > + *  - dest always begins at 0 while xAPIC MDA has offset 24,
> > + *  - IOxAPIC messages have to be delivered (directly) to x2APIC.
> > + */
> > +static u32
> > +kvm_apic_mda(unsigned int dest, struct kvm_lapic *ipi, bool x2apic_dest)
> 
> Please pass two struct kvm_lapic, so that you can write
> 
> 	bool ipi = source != NULL;
> 	bool x2apic_mda = apic_x2apic_mode(ipi ? source : dest);
> 
> Looks a little nicer to me at least.

Definitely.

> > +{
> > +	bool x2apic_mda = ipi ? apic_x2apic_mode(ipi) : x2apic_dest;
> > +
> > +	if (!ipi && dest == APIC_BROADCAST)
> > +		dest = X2APIC_BROADCAST;
> 
> This works, but it is not super-clear that you are shifting left by 24
> here, and right in kvm_apic_broadcast().  What if you just make it
> 
> 	if (!ipi && dest == APIC_BROADCAST && x2apic_mda)
> 		return X2APIC_BROADCAST.

It's better, it will be that way in v2 of [5-8/8], thanks.

(I was using it twice in earlier iterations and didn't think again.)
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