Right now the routine leaves the current CPU in the map, later tripping on an assert when filling in the scoreboard:
panic: IPI scoreboard is zero, initiator 1 target 1

Instead pre-check if all CPUs are present in the map and remember that outcome for later.

Fixes 7eaea04a5bb1dc ("amd64: compare TLB shootdown target to all_cpus")

As a side note this code looks weirdly inefficient. For example the initial scoreboard loop should have a form of FOREACH macro instead of ffsing from scratch every time. That goes beyond the scope of this change, I may get around to it later.