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    SubjectRe: [PATCH v4] x86, vt-d: enable x2apic opt out
    On Wed, 25 May 2011, Ingo Molnar wrote:

    > * Youquan Song <> wrote:
    > > New version of VT-d2 specification
    > > (
    > > /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.



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