HEAD/6.1_RC2 DOM0 problems?

[Jeff Rizzo <riz%tastylime.net@localhost>]

I just tried a 6.1_RC2 dom0 kernel on a dual opteron box which was 
working fine with a pre-6.0 dom0 kernel, and which works fine with a 
6.1_RC2 GENERIC.  Things seem to start booting ok, then
really slow down once they get to wd1, and eventually hang altogether.  
I've seen it get as far as:

root file system type: ffs

... but I've also seen it hang slightly earlier (after detecting wd1, 
somewhere in the USB).

I tried a 6.0.1 dom0 kernel, and it works fine.  A -current dom0 from 
20130322, though, hangs *even earlier*:

NetBSD 6.99.18 (XEN3_DOM0) #0: Fri Mar 22 12:55:23 UTC 2013
builds%b8.netbsd.org@localhost:/home/builds/ab/HEAD/amd64/201303221130Z-obj/home/builds/ab/HEAD/src/sys/arch/amd64/compile/XEN3_DOM0
total memory = 256 MB
avail memory = 232 MB
mainbus0 (root)
cpu0 at mainbus0 apid 0
cpu1 at mainbus0 apid 2
cpu2 at mainbus0 apid 1
cpu3 at mainbus0 apid 3
ioapic0 at mainbus0 apid 4
(XEN) ioapic_guest_write: apic=0, pin=0, irq=0
(XEN) ioapic_guest_write: new_entry=000109f0
(XEN) ioapic_guest_write: old_entry=00010000 pirq=0
(XEN) ioapic_guest_write: Attempt to modify IO-APIC pin for in-use IRQ!
(XEN) ioapic_guest_write: apic=0, pin=2, irq=0
(XEN) ioapic_guest_write: new_entry=000109f0
(XEN) ioapic_guest_write: old_entry=000009f0 pirq=0
(XEN) ioapic_guest_write: Attempt to modify IO-APIC pin for in-use IRQ!
(XEN) irq.c:1514: dom0: pirq 0 or irq 3 already mapped
(XEN) ioapic_guest_write: apic=0, pin=4, irq=4
(XEN) ioapic_guest_write: new_entry=000109f1
(XEN) ioapic_guest_write: old_entry=000009f1 pirq=0
(XEN) ioapic_guest_write: Attempt to modify IO-APIC pin for in-use IRQ!
(XEN) irq.c:1514: dom0: pirq 0 or irq 5 already mapped
(XEN) irq.c:1514: dom0: pirq 0 or irq 6 already mapped
(XEN) irq.c:1514: dom0: pirq 0 or irq 7 already mapped
(XEN) irq.c:1514: dom0: pirq 0 or irq 8 already mapped
(XEN) irq.c:1514: dom0: pirq 0 or irq 9 already mapped
(XEN) irq.c:1514: dom0: pirq 0 or irq 10 already mapped
(XEN) irq.c:1514: dom0: pirq 0 or irq 11 already mapped
(XEN) irq.c:1514: dom0: pirq 0 or irq 12 already mapped
(XEN) irq.c:1514: dom0: pirq 0 or irq 13 already mapped
ioapic0: can't remap to apid 4
ioapic1 at mainbus0 apid 5
ioapic1: can't remap to apid 5
ioapic2 at mainbus0 apid 6

<hang>


...does anyone know what might be happening?  This seems like something 
we should try to fix before release.  :)

+j