linux-kernel - Re: [PATCH v4] x86, vt-d: enable x2apic opt out

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Message-ID: <20110525205843.GC28397@elte.hu>
Date:	Wed, 25 May 2011 22:58:43 +0200
From:	Ingo Molnar <mingo@...e.hu>
To:	Youquan Song <youquan.song@...el.com>
Cc:	linux-kernel@...r.kernel.org, david.woodhouse@...el.com,
	akpm@...ux-foundation.org, tglx@...utronix.de, hpa@...or.com,
	hpa@...ux.intel.com, allen.m.kay@...el.com,
	suresh.b.siddha@...el.com, rajesh.sankaran@...el.com,
	asit.k.mallick@...el.com, kent.liu@...el.com,
	Youquan Song <youquan.song@...ux.intel.com>
Subject: Re: [PATCH v4] x86, vt-d: enable x2apic opt out


* Youquan Song <youquan.song@...el.com> wrote:

> New version of VT-d2 specification 
> (http://download.intel.com/technology 
> /computing/vptech/Intel(r)_VT_for_Direct_IO.pdf) includes a new 
> feature that provide firmware a way to request system software to 
> opt out of enable x2APIC mode. DMAR ACPI table newly define flags.1 
> bit: x2APIC_OPT_OUT which is set to request System software opt out 
> xAPIC mode if flags.0 bit:INTR_REMAP is also set.

So why isnt the x2apic disabled in the CPUID? That's the canonical 
way to unsupport a particular non-working CPU hw feature.

Thanks,

	Ingo
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