linux-kernel - Re: [PATCH 8/8] KVM: x86: simplify kvm_apic

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Date:	Fri, 30 Jan 2015 22:15:45 +0100
From:	Paolo Bonzini <pbonzini@...hat.com>
To:	Radim Krčmář <rkrcmar@...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 8/8] KVM: x86: simplify kvm_apic_map



On 30/01/2015 17:57, Radim Krčmář wrote:
> As optimizations go, we could drop the "&" on cid as "cid < 16" is
> checked later, so mode=4 practically does nothing ... Not the best for
> future bugs, but still pretty safe -- only x2APIC can set a value that
> would require the "&" and it can't have valid XAPIC mode, so u32 still
> protects us enough.
> 
>   *cid = ldr >> mode;
>   *lid = ldr & ((1 << mode) - 1);
> 
> Which is probably faster a solution where we don't shuffle switch cases
> to jump to x2APIC first.  A comparison is at the very bottom [2].
> 
> Would that be ok in v2?

Yes, this is okay.  Thanks for looking at it!

Paolo
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