bhyve vlapic needs ability to bypass isrvec_stk
The emulated APIC in bhyve (vlapic) contains a data structure
isrvec_stk which tracks the vectors of delivered interrupts for the purpose of asserting certain invariants. While the use of
ifdef around pieces relating to
isrvec_stk might make it seem as if it's just an additional check on top of the standard logic, it is (via
vlapic_update_ppr) load bearing. The same data could be effectively derived from the
isr0-7 registers in the LAPIC page. Considering that the state contained in
isrvec_stk is a bhyve implementation detail, rather than architecturally defined, it would be nice if it could be omitted. This is especially true for save/restore or live-migrate cases, where that
isrvec_stk data would need to be rehydrated and/or its checks disabled, lest the new host running the VM fail an assert because the architectural and implementation states differ.
The logic itself could be kept around for debugging purposes, but in a way that makes it optional.