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


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