[Bug 293907] guest kernel fails to init when vcpus > available cpus set by cpuset

https://bugs.freebsd.org/bugzilla/show_bug.cgi?id=293907

            Bug ID: 293907
           Summary: guest kernel fails to init when vcpus > available cpus
                    set by cpuset
           Product: Base System
           Version: 16.0-CURRENT
          Hardware: Any
                OS: Any
            Status: New
          Severity: Affects Only Me
          Priority: ---
         Component: kern
          Assignee: bugs@FreeBSD.org
          Reporter: nvass@gmx.com

I have a system with 12 cpu cores and a virtual machine with 12 cpu cores. I
wanted to temporarily limit the VM to six cpu cores so I created a cpuset with
6 cpu cores. The guest kernel failed to init. It reached "Launching APs: 2 8 6
11 10 9 3 4 7 5 1" and stayed there spinning.

Steps to reproduce:
# cpuset -g -p $$
pid 74790 mask: 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11
pid 74790 domain policy: first-touch mask: 0
# grep cpu /aurora-storage/vms-danae/devel/devel.conf
cpu=12

# cpuset -C -l 0-5 -p $$
# cpuset -g -p $$
pid 74790 mask: 0, 1, 2, 3, 4, 5
pid 74790 domain policy: first-touch mask: 0
# vm start devel
console output:
---<<BOOT>>---
Copyright (c) 1992-2026 The FreeBSD Project.
Copyright (c) 1979, 1980, 1983, 1986, 1988, 1989, 1991, 1992, 1993, 1994
        The Regents of the University of California. All rights reserved.
FreeBSD is a registered trademark of The FreeBSD Foundation.
FreeBSD 16.0-CURRENT main-n284539-1d13d938fe6c GENERIC amd64
FreeBSD clang version 19.1.7 (https://github.com/llvm/llvm-project.git
llvmorg-19.1.7-0-gcd708029e0b2)
WARNING: WITNESS option enabled, expect reduced performance.
VT: init without driver.
CPU: Intel(R) Xeon(R) CPU           X5650  @ 2.67GHz (2666.77-MHz K8-class CPU)
  Origin="GenuineIntel"  Id=0x206c2  Family=0x6  Model=0x2c  Stepping=2
 
Features=0x9f83fbff<FPU,VME,DE,PSE,TSC,MSR,PAE,MCE,CX8,APIC,SEP,MTRR,PGE,MCA,CMOV,PAT,PSE36,MMX,FXSR,SSE,SSE2,SS,HTT,PBE>
 
Features2=0x829e6217<SSE3,PCLMULQDQ,DTES64,DS_CPL,SSSE3,CX16,xTPR,PCID,DCA,SSE4.1,SSE4.2,POPCNT,AESNI,HV>
  AMD Features=0x2c100800<SYSCALL,NX,Page1GB,RDTSCP,LM>
  AMD Features2=0x1<LAHF>
  TSC: P-state invariant
Hypervisor: Origin = "bhyve bhyve "
real memory  = 5372903424 (5124 MB)
avail memory = 4109144064 (3918 MB)
Event timer "LAPIC" quality 600
ACPI APIC Table: <BHYVE  BVAPIC >
FreeBSD/SMP: Multiprocessor System Detected: 12 CPUs
FreeBSD/SMP: 12 package(s) x 1 core(s)
random: unblocking device.
ioapic0 <Version 1.1> irqs 0-31
Launching APs: 2 8 6 11 10 9 3 4 7 5 1

Not sure whether this is a host or guest kernel problem...

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