panic: pmap_emulate_reference(0xfffffc0022ec4c80, 0xfffffe0014487e68, 0, 1): pa 0x1d514000 not managed

One of the alpha package machines died just now with:

panic: pmap_emulate_reference(0xfffffc0022ec4c80, 0xfffffe0014487e68, 0, 1): pa 0x1d514000 not managed
at line 2585 in file /a/asami/portbuild/alpha/src-client/sys/alpha/alpha/pmap.c
Stack backtrace:
db_print_backtrace() at db_print_backtrace+0x18
backtrace() at backtrace+0x2c
__panic() at __panic+0x150
pmap_emulate_reference() at pmap_emulate_reference+0x15c
trap() at trap+0x39c
XentMM() at XentMM+0x2c
--- memory management fault (from ipl 7) ---
pmap_activate() at pmap_activate+0xb4
Lcs1() at Lcs1+0x1c
--- root of call graph ---
panic
Stopped at      Debugger+0x38:  zapnot  v0,#0xf,v0      <v0=0x7>
db>

Kris