Description of problem:
Choosing qxl as video device in virt-manager i get offered 64 MB RAM.
Aside from the question, if this makes sense, i got it offered, it was
not possible to change this parameter in the GUI.

The X-Server did not start (neither with a manually written xorg.conf
nor when starting with -configure) writing this error to the Xorg.0.log:
(EE) Screen(s) found, but none have a usable configuration.

Trying to find out what happens, shows: When trying to map the video
memory, the program gets back EAGAIN from the virtual machine. Increasing
the maximum locked memory (ulimit -l) to 200 MB (the virtual instance has
2 GB memory with the hardware having 32 GB physical memory) did not help
(i'd assume the program/driver itself would increase this resource limit)

It happens in
libpciaccess's linux_sysfs.c, line 569 (the one containing mmap)
function pci_device_linux_sysfs_map_range, called from
libpciaccess's common_interface.c, line 312, function pci_device_map_range
when calling the map_range method: pci_sys->methods->map_range, called from
qxl_driver.c, line 238, function qxl_map_memory, calling pci_device_map_range
the 2nd time for the video ram with &qxl->vram as last argument.
It fails wtih 64 MB (actually anything > 32MB)

The error message is almost meaningless.

Version-Release number of selected component (if applicable):
0.0.21-3.fc15

How reproducible:
Accepting the suggested 64 MB video RAM with qxl
and trying to get X11 running on the virtual video device

Steps to Reproduce:
1. Create a virtual machine with virt-manager
2. When it comes to the video device, choose qxl and accept the suggested 64 MB RAM
3. Try to start X11 in the virtual instance (whatever way)
  
Actual results:
Error message Screen(s) found, but none have a usable configuration.
And no X11 graphics windowing system running

Expected results:
X11 works

Additional info:
choosing 9 MB video RAM it works.
To get this suggested by virt-manager is magic. Remove the video device.
It is automatically created again with 9 MB video RAM. However, the video
RAM can be configured in QEMU's xml configuration file if one does not
manage to do this in the virt-manager (who seems a bit weird to me in
some places e.g. unclear defaults). Playing with this it turned out, that
Xorg-qxl works with up to 32 MB video ram and not with 33 MB.
Probably some component should just automatically limit this value to
32 MB.
So frankly i don't know, whether it's actually a problem in qemu when
doing the mmap.
It does not help to increase the maximum locked memory limit when
starting libvirtd and / or the virt-manager.