Created attachment 510972 [details]
three scheenshots of the environment at the time anaconda tries to search for storage devices

Description of problem:
using a xen Dom0 (centos5.6), when a stock fc15 x86_64 image is used to install a HVM, the virtual block devices are not recognized by/available to the os for installation. I have attached screenshots of what the shell sees (lsmod;lspci;cat /proc/partitions) at the time it scans for storage devices. 

Version-Release number of selected component (if applicable):
not sure. current fedora 15 build available on the mirrors.

How reproducible:
install unmodified fedora 15 x86_64 to a xen HVM domU via pxe/cd/netboot

Steps to Reproduce:
1.establish functioning xen4.1.0(or earlier) dom0 x86_64 host
2.build a functional VM/domU, pointing to a x86_64 fc15 install target
3.boot up the VM and watch the install
  
Actual results:
no virtual block devices found by the anaconda; installation dies.

Expected results:
the guest os sees the virtual disks as an IDE disk drive.

Additional info:

http://lists.xensource.com/archives/html/xen-devel/2011-07/msg00062.html

I've been able to work around this bug by passing "xen_emul_unlug=never" to the kernel at boot time. However, including the xen-platform-pci.ko and xen-blkfront.ko modules in the initrd or toggling the appropriate kernel flags from =m to =y should fix it as well.

I don't see this bug in the 1386 image.