Linux reboots with no panic when booting SMP configuration from kexec

I'm working on a project involving kexec. I have it working on some of our hardware platforms. On one platform, I'm getting sudden reboots with no panic dump during SMP setup:

[   25.219028] smpboot: CPU0: AMD EPYC 7402 24-Core Processor (family: 0x17, model: 0x31, stepping: 0x0)
[   25.228083] Performance Events: Fam17h+ core perfctr, AMD PMU driver.
[   25.237997] ... version:                0
[   25.247996] ... bit width:              48
[   25.257996] ... generic registers:      6
[   25.267996] ... value mask:             0000ffffffffffff
[   25.277996] ... max period:             00007fffffffffff
[   25.287996] ... fixed-purpose events:   0
[   25.297996] ... event mask:             000000000000003f
[   25.308059] rcu: Hierarchical SRCU implementation.
[   25.318046] NMI watchdog: Enabled. Permanently consumes one hw-PMU counter.
[   25.328283] smp: Bringing up secondary CPUs ...
[   25.335543] x86: Booting SMP configuration:
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This platform boots fine under normal (i.e., non-kexec) circumstances. The primary and kexec kernels are built from the same codebase but linked differently - this is unlikely to be related to the issue because I've already tested this on an Intel platform. Kexec command line:

[    0.000000] Command line: elfcorehdr=0x86000000 ro panic=5 console=ttyS0,9600 loglevel=8 numifbs=0 nf_conntrack.acct=1 nmi_watchdog=1 profile=0 root=/dev/ram0 initrd=/crashfs.gz libata.force=disable

BIOS - may be relevant since one boot is with and one is without the BIOS:

Version 2.20.1275. Copyright (C) 2022 American Megatrends, Inc.
BIOS V1.05(08/26/2022)

I've tracked it down to wakeup_secondary_cpu_via_init in arch/x86/kernel/smpboot.c. The last output I get is just before the first apic_icr_write. I don't know where to even begin debugging this. Could it possibly be the NMI watchdog forcing a reboot because the only available core is hanging for some reason? Seems unlikely since that hung core wouldn't be able to perform NMI checks.