panic: tsb_tte_enter: replacing valid kernel mapping

Got this at boot time on a 12-processor e4500 running 6.0-RC1:

FreeBSD 6.0-RC1 #18: Tue Oct 18 15:31:13 JST 2005
    root_at_e4500-3.allbsd.org:/usr/src/sys/sparc64/compile/E4500_3
WARNING: WITNESS option enabled, expect reduced performance.
real memory  = 9663676416 (9216 MB)
avail memory = 9434734592 (8997 MB)
cpu0: Sun Microsystems UltraSparc-II Processor (400.00 MHz CPU)
cpu1: Sun Microsystems UltraSparc-II Processor (400.00 MHz CPU)
cpu2: Sun Microsystems UltraSparc-II Processor (400.00 MHz CPU)
cpu3: Sun Microsystems UltraSparc-II Processor (400.00 MHz CPU)
cpu4: Sun Microsystems UltraSparc-II Processor (400.00 MHz CPU)
cpu5: Sun Microsystems UltraSparc-II Processor (400.00 MHz CPU)
cpu6: Sun Microsystems UltraSparc-II Processor (400.00 MHz CPU)
cpu7: Sun Microsystems UltraSparc-II Processor (400.00 MHz CPU)
cpu8: Sun Microsystems UltraSparc-II Processor (400.00 MHz CPU)
cpu9: Sun Microsystems UltraSparc-II Processor (400.00 MHz CPU)
cpu10: Sun Microsystems UltraSparc-II Processor (400.00 MHz CPU)
cpu11: Sun Microsystems UltraSparc-II Processor (400.00 MHz CPU)
FreeBSD/SMP: Multiprocessor System Detected: 12 CPUs
panic: tsb_tte_enter: replacing valid kernel mapping
cpuid = 0
KDB: enter: panic
[thread pid 0 tid 0 ]
Stopped at      kdb_enter+0x3c: ta              %xcc, 1
db> wh
Tracing pid 0 tid 0 td 0xc041b6e8
panic() at panic+0x164
tsb_tte_enter() at tsb_tte_enter+0x7c
pmap_enter() at pmap_enter+0x2ec
kmem_malloc() at kmem_malloc+0x394
page_alloc() at page_alloc+0x18
uma_large_malloc() at uma_large_malloc+0x34
malloc() at malloc+0x134
sf_buf_init() at sf_buf_init+0x78
mi_startup() at mi_startup+0x12c
btext() at btext+0x34
db>