x86_64 - Unable to boot DomU

[David F Barrera <dfbp@us.ibm.com>]

I've built Xen with the latest hg source pull, and I am not able to boot 
domU on my x86_64 boxes using configurations and setups that have 
previously worked. Has something changed since late last week that would 
require a change in my domU configuration file?

When creating DomU, I get the following error message:

VFS: Cannot open root device "sdb2" or unknown-block(0,0)
Please append a correct "root=" boot option
Kernel panic - not syncing: VFS: Unable to mount root fs on 
unknown-block(0,0)

The file system for DomU is ext3, and I've made sure that it is built in 
xenU kernel.

This are the xm dmesg lines displayed when error occurs:

(XEN) (file=grant_table.c, line=1071) Grant unref rd(5) ld(0) frm(d485) 
flgs(0).
(XEN) (file=traps.c, line=878) Non-priv domain attempted 
RDMSR(00000000c0000080,00020000,00020000).
(XEN) (file=traps.c, line=870) Non-priv domain attempted 
WRMSR(00000000c0000100,00000000,00000000).
(XEN) (file=traps.c, line=870) Non-priv domain attempted 
WRMSR(00000000c0000102,00000000,00000000).
(XEN) (file=traps.c, line=878) Non-priv domain attempted 
RDMSR(00000000c0000080,00000000,00000000).
stop_this_cpu disable_local_apic

This is the domU configuration file:

# Kernel image file.
kernel = "/boot/vmlinuz-2.6-xenU"
# Optional ramdisk.
# ramdisk = "/boot/initrd-2.6.11.12-xenU"
# The domain build function. Default is 'linux'.
builder='linux'
# Initial memory allocation (in megabytes) for the new domain.
# memory = 256
memory = 512
# A name for your domain. All domains must have different names.
name = "vm1"
disk = [ 'phy:sdb1,0811,w','phy:sdb2,0812,w' ]
# Set if you want dhcp to allocate the IP address.
# vif = [ 'mac= AA:00:00:47:CB:34, bridge=xen-br0' ]
# Set if you want dhcp to allocate the IP address.
#dhcp="dhcp"
# Set netmask.
#netmask = '255.255.255.0'
# Set default gateway.
# gateway = '9.53.94.0'
# Set the hostname.
# hostname= "vm%d" % vmid


# Set root device.
root = "/dev/sdb2 ro"
# Sets runlevel 4.
# extra = "4"
#==============

David F Barrera