Hi Neel,
Thank you for getting back to us on this.
> I was able to debug this by making modifications to the guest and it seems that the IOAPIC emulation is treating the destination APIC ID as a 32-bit value if x2apic is enabled (as opposed to using the high 8 bits just like in xAPIC mode). This is not compliant with the x2APIC specification.
I don't believe that the behavior of programming the IOAPIC with legacy style entries is architecturally defined when x2APIC is enabled. The Intel SDM indicates that the IOAPIC entries must be in the new re-mappable format:
"Routing of device interrupts to local APIC units operating in x2APIC mode requires use of the interrupt-remapping architecture specified in the Intel® Virtualization Technology for Directed I/O, Revision 1.3".
Neither Linux nor Windows will use x2APIC with legacy style IOAPIC entries - they both require VT-D and program the IOAPIC with remappable format interrupts. If you don't mind answering a few more questions - when you booted this natively on a bare metal Intel Xeon system were you using VT-D and interrupt remapping? If no have you tried it on Sandybridge? How many CPUs were you using on the Xeon system?
Thanks,
Doug