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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
Date: Thu, 26 May 2011 00:01:19 +0200 (CEST)	[thread overview]
Message-ID: <alpine.LFD.2.02.1105252359460.3078@ionos> (raw)
In-Reply-To: <20110525205843.GC28397@elte.hu>

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

  reply	other threads:[~2011-05-25 22:01 UTC|newest]

Thread overview: 5+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2011-05-25 16:36 Youquan Song
2011-05-25 20:58 ` Ingo Molnar
2011-05-25 22:01   ` Thomas Gleixner [this message]
2011-05-25 23:37     ` Woodhouse, David
2011-06-09 15:34       ` Youquan Song

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