Date: Thu, 26 May 2011 00:01:19 +0200 (CEST)
From: Thomas Gleixner <tglx@linutronix.de>
To: Ingo Molnar <mingo@elte.hu>
cc: Youquan Song <youquan.song@intel.com>, linux-kernel@vger.kernel.org,
        david.woodhouse@intel.com, akpm@linux-foundation.org, hpa@zytor.com,
        hpa@linux.intel.com, allen.m.kay@intel.com, suresh.b.siddha@intel.com,
        rajesh.sankaran@intel.com, asit.k.mallick@intel.com,
        kent.liu@intel.com, Youquan Song <youquan.song@linux.intel.com>
Subject: Re: [PATCH v4] x86, vt-d: enable x2apic opt out
In-Reply-To: <20110525205843.GC28397@elte.hu>
Message-ID: <alpine.LFD.2.02.1105252359460.3078@ionos>
References: <1306341418-10645-1-git-send-email-youquan.song@intel.com> <20110525205843.GC28397@elte.hu>
User-Agent: Alpine 2.02 (LFD 1266 2009-07-14)
MIME-Version: 1.0
Content-Type: TEXT/PLAIN; charset=US-ASCII
Sender: linux-kernel-owner@vger.kernel.org
Content-Length: 1050
Lines: 27

On Wed, 25 May 2011, Ingo Molnar wrote:

> 
> * Youquan Song <youquan.song@intel.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.

Because some committee decided to make it an ACPI feature. That's
broken by design, but you can't change the stupid spec retroactively.

Thanks,

	tglx
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@vger.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/