linux-kernel - Re: [patch 00/26] x64, x2apic/intr-remap: Interrupt-remapping and x2apic support

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Message-ID: <20080713010000.GA1678@linux-os.sc.intel.com>
Date:	Sat, 12 Jul 2008 18:00:01 -0700
From:	Suresh Siddha <suresh.b.siddha@...el.com>
To:	Yinghai Lu <yhlu.kernel@...il.com>
Cc:	"Eric W. Biederman" <ebiederm@...ssion.com>,
	"Siddha, Suresh B" <suresh.b.siddha@...el.com>,
	Ingo Molnar <mingo@...e.hu>, "hpa@...or.com" <hpa@...or.com>,
	"tglx@...utronix.de" <tglx@...utronix.de>,
	"akpm@...ux-foundation.org" <akpm@...ux-foundation.org>,
	"arjan@...ux.intel.com" <arjan@...ux.intel.com>,
	"andi@...stfloor.org" <andi@...stfloor.org>,
	"jbarnes@...tuousgeek.org" <jbarnes@...tuousgeek.org>,
	"steiner@....com" <steiner@....com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"jeremy@...p.org" <jeremy@...p.org>
Subject: Re: [patch 00/26] x64, x2apic/intr-remap: Interrupt-remapping and x2apic support

On Fri, Jul 11, 2008 at 11:17:02PM -0700, Yinghai Lu wrote:
> also read the x2APIC spec pdf, it doesn't say anything about interrupt
> remapping...need to be used with x2apic...

We are updating the spec with more clarifications. But in short,
intr-remapping needs to be enabled prior to enabling x2apic in the CPU.

physical mode might work for < 255 id's for some. But it is HW
implementation specific and might not work from generation to generation.
chipsets or cpu's may drop the interrupts if cpu and chipset are
in different modes (one in legacy mode and another in extended).

So Intel is recommending to enable Intr-remapping before enabling x2apic.

thanks,
suresh
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