FreeBSD/src b280235 (r354637)sys/x86/xen xen_apic.c

xen: fix dispatching of NMIs

Currently NMIs are sent over event channels, but that defeats the
purpose of NMIs since event channels can be masked. Fix this by
issuing NMIs using a hypercall, which injects a NMI (vector #2) to the
desired vCPU.

Note that NMIs could also be triggered using the emulated local APIC,
but using a hypercall is better from a performance point of view
since it doesn't involve instruction decoding when not using x2APIC
mode.

Reported and Tested by: avg
Sponsored by:           Citrix Systems R&D
DeltaFile
+40-10sys/x86/xen/xen_apic.c
+40-101 files

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