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

[Thomas Gleixner]

On Wed, 25 May 2011, Ingo Molnar wrote:

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