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    SubjectRe: [PATCH 4/4] KVM: x86: allow hotplug of VCPU with APIC ID over 0xff
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    Am 02.12.2016 um 20:44 schrieb Radim Krčmář:
    > LAPIC after reset is in xAPIC mode, which poses a problem for hotplug of
    > VCPUs with high APIC ID, because reset VCPU is waiting for INIT/SIPI,
    > but there is no way to uniquely address it using xAPIC.
    >
    > From many possible options, we chose the one that also works on real
    > hardware: accepting interrupts addressed to LAPIC's x2APIC ID even in
    > xAPIC mode.
    >
    > KVM intentionally differs from real hardware, because real hardware
    > (Knights Landing) does just "x2apic_id & 0xff" to decide whether to
    > accept the interrupt in xAPIC mode and it can deliver one interrupt to
    > more than one physical destination, e.g. 0x123 to 0x123 and 0x23.
    >
    > Add a capability to let userspace know that we do something now.

    Should we allow user space to turn it on/off for compatibility handling?
    Or do we just not care? (or how will this capability be used later on?)



    --

    David

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