When booting from a PCIe ExpressModule or a Fabric Expansion Module (FEM), the system might hang because it runs out of MSI interrupt vectors.
Workaround
In the GRUB configuration, set pci=nomsi.
Boot a non-Xen kernel.
Edit the file /boot/grub/menu.lst.
Add the following text to the Xen kernel init line stanza:
pci=nomsi
For example:
# grub.conf generated by anaconda # # Note that you do not have to rerun grub after making changes to this file # NOTICE: You have a /boot partition. This means that # all kernel and initrd paths are relative to /boot/, eg. # root (hd0,0) # kernel /vmlinuz-version ro root=/dev/sda3 # initrd /initrd-version.img #boot=/dev/sda default=1 timeout=5 serial --unit=0 --speed=115200 terminal --timeout=5 serial console title Enterprise Linux Server (2.6.18-194.el5xen) root (hd0,0) kernel /xen.gz-2.6.18-194.el5 com1=115200 console=com1 module /vmlinuz-2.6.18-194.el5xen ro root=LABEL=/ console=ttyS0,115200 debug pci=nomsi module /initrd-2.6.18-194.el5xen.img title Enterprise Linux Server-base (2.6.18-194.el5) root (hd0,0) kernel /vmlinuz-2.6.18-194.el5 ro root=LABEL=/ earlylprintk=ttyS0,115200 console=ttyS0,115200 debug initrd /initrd-2.6.18-194.el5.img
or
Reboot the Xen kernel.