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?)
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