vcnt()/vcnt_intr() accumulate u_int per-CPU counters into signed int, wrapping vm.stats.* exports negative after 2^31 aggregate events

Summary

Every vm.stats.sys. and vm.stats.vm. counter is exported by vcnt(), which declares int count and sums u_int per-CPU fields across all CPUs; vcnt_intr() likewise. Once the cross-CPU sum exceeds 2^31 (or any single CPU's counter passes 2^31 — reachable in days on a busy box at ~10k ctx switches/s/CPU), the exported value wraps negative/incorrect. Correctness/hardening in exported accounting only — the int goes straight to userland stat consumers (systat, top) with no in-kernel reader; no security impact. Fix: accumulate u64, export u_int (row diff).

Timeline

• 2026-09-02 Discovered during pass-2 audit of vm_meter.c (GLM 5.3).