[Bug 274840] devmatch kernel panic with 10 xn interfaces

https://bugs.freebsd.org/bugzilla/show_bug.cgi?id=274840

            Bug ID: 274840
           Summary: devmatch kernel panic with 10 xn interfaces
           Product: Base System
           Version: 14.0-RELEASE
          Hardware: amd64
                OS: Any
            Status: New
          Severity: Affects Many People
          Priority: ---
         Component: kern
          Assignee: bugs@FreeBSD.org
          Reporter: andrew@netplex.net

Created attachment 246037
  --> https://bugs.freebsd.org/bugzilla/attachment.cgi?id=246037&action=edit
core.txt

Running devmatch (at boot time or after boot) with 10 Xen "xn" interfaces
causes a kernel panic crash. With fewer interfaces it does not crash. Adding
many interfaces with the system on-line (not running devmatch) does not crash.

Tested and effects 13.2-p4 and 14.0-RC3.
This also cause problems with FreeBSD based apps like OPNsense and PFsense.

Running on XCP 8.2.1 (Xen). Running FreeBSD amd64 GENERIC kernel

```
FreeBSD  14.0-RC3 FreeBSD 14.0-RC3 #0 releng/14.0-n265368-c6cfdc130554: Fri Oct
27 05:57:28 UTC 2023    
root@releng1.nyi.freebsd.org:/usr/obj/usr/src/amd64.amd64/sys/GENERIC  amd64

panic: page fault

Reading symbols from /boot/kernel/kernel...
Reading symbols from /usr/lib/debug//boot/kernel/kernel.debug...

Unread portion of the kernel message buffer:


Fatal trap 12: page fault while in kernel mode
cpuid = 0; apic id = 00
fault virtual address   = 0x0
fault code              = supervisor read data, page not present
instruction pointer     = 0x20:0xffffffff81008a64
stack pointer           = 0x28:0xfffffe0076295b30
frame pointer           = 0x28:0xfffffe0076295b30
code segment            = base 0x0, limit 0xfffff, type 0x1b
                        = DPL 0, pres 1, long 1, def32 0, gran 1
processor eflags        = interrupt enabled, resume, IOPL = 0
current process         = 3078 (devmatch)
rdi: 0000000000000000 rsi: 0000000000000000 rdx: 0000000000000018
rcx: 0000000000000000  r8: fefefefefefefeff  r9: 8080808080808080
rax: fffff80006f99000 rbx: 0000000000000000 rbp: fffffe0076295b30
r10: 0000000000000000 r11: df9290bcccff8d9a r12: 0000000000000002
r13: 0000000000000002 r14: fffffe0076295b68 r15: fffff8007419c000
trap number             = 12
panic: page fault
cpuid = 0
time = 1698809363
KDB: stack backtrace:
#0 0xffffffff80b9002d at kdb_backtrace+0x5d
#1 0xffffffff80b43132 at vpanic+0x132
#2 0xffffffff80b42ff3 at panic+0x43
#3 0xffffffff8100c85c at trap_fatal+0x40c
#4 0xffffffff8100c8af at trap_pfault+0x4f
#5 0xffffffff80fe3818 at calltrap+0x8
#6 0xffffffff80b9c515 at sbuf_cat+0x15
#7 0xffffffff80b83d55 at sysctl_devices+0x125
#8 0xffffffff80b54910 at sysctl_root_handler_locked+0x90
#9 0xffffffff80b53d41 at sysctl_root+0x241
#10 0xffffffff80b543c6 at userland_sysctl+0x176
#11 0xffffffff80b5420c at sys___sysctl+0x5c
#12 0xffffffff8100d119 at amd64_syscall+0x109
#13 0xffffffff80fe412b at fast_syscall_common+0xf8
Uptime: 2m6s
Dumping 268 out of 4059 
```

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