By default, the hypervisor will not use a serial console itself. To enable
it (allowing debugging information and access), you will need to modify
/boot/grub/menu.lst as follows. If your serial console is on ttya in
Solaris (check eeprom if you're not sure), then add an entry similar
to the following:
title Solaris xVM with serial console
kernel$ /boot/$ISADIR/xen.gz console=com1 com1=auto
module$ /platform/i86xpv/kernel/$ISADIR/unix /platform/i86xpv/kernel/$ISADIR/unix
module$ /platform/i86pc/$ISADIR/boot_archive
If the console is on ttyb in Solaris, then use com2 appropriately.