linux-kernel - Re: [PATCH] decouple x2apic from irq remapping

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Message-ID: <20090219113018.GS2354@elte.hu>
Date:	Thu, 19 Feb 2009 12:30:18 +0100
From:	Ingo Molnar <mingo@...e.hu>
To:	Gleb Natapov <gleb@...hat.com>
Cc:	linux-kernel@...r.kernel.org, yinghai@...nel.org,
	"H. Peter Anvin" <hpa@...or.com>,
	Thomas Gleixner <tglx@...utronix.de>
Subject: Re: [PATCH] decouple x2apic from irq remapping


* Gleb Natapov <gleb@...hat.com> wrote:

> Hi,
> 
> Currently x2apic is used only if interrupt remapping can be enabled,
> but if all apic ids are smaller then 255 there is no reason to
> enable interrupt remapping at all. Although there is not real HW that has
> x2apic but does not have IR the decoupling is useful since we want to
> emulate x2apic interface in KVM (it is more vitalization friendly), but
> we don't want to emulate IR just for that.
> 
> According to Intel docs BIOS should pass control to OS in x2apic mode 
> if there are apics with id > 255 and in xapic otherwise, so the proposed
> patch requires IR configuration only if BIOS switched apic to x2apic
> mode.
> 
> The patch is against tip:x86/apic.

Applied to tip:x86/apic, thanks Gleb!

	Ingo
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