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Description of problem:
Whenever I try to start a virtual machine on my RHEL-6 host, I get this error message:

johanka:~# LANG=C virsh start tikanga
error: Failed to start domain tikanga
error: internal error Process exited while reading console log output: Supported machines are:
pc         RHEL 6.0.0 PC (alias of rhel6.0.0)
rhel6.0.0  RHEL 6.0.0 PC (default)
rhel5.5.0  RHEL 5.5.0 PC
rhel5.4.4  RHEL 5.4.4 PC
rhel5.4.0  RHEL 5.4.0 PC

Which (aside from being completely unhelpful ... which machine we are talking about here? host or guest?) is just wrong. My host is RHEL-6, guest RHEL-5

Version-Release number of selected component (if applicable):
johanka:~# rpm -q libvirt qemu-kvm
libvirt-0.8.1-15.el6.x86_64
qemu-kvm-0.12.1.2-2.96.el6.x86_64


How reproducible:


Steps to Reproduce:
1.
2.
3.
  
Actual results:


Expected results:


Additional info:

RHEL-4 guest starts without a problem.

When I changed via

virsh edit tikanga 

line

<type arch='x86_64' machine='pc-0.12'>hvm</type>

to 

<type arch='x86_64' machine='pc'>hvm</type>

guest starts again.

Is this a regression or wasn't this supposed to work all the time and it was just a mistake that it did?

This issue has been proposed when we are only considering blocker
issues in the current Red Hat Enterprise Linux release.

** If you would still like this issue considered for the current
release, ask your support representative to file as a blocker on
your behalf. Otherwise ask that it be considered for the next
Red Hat Enterprise Linux release. **

libvirt should've selected a rhel-5 machine type for your installation. Using pc-0.12 was wrong; was this guest installed a while ago?

Earlier version of RHEL6 kvm still included the 'pc-0.12' machine type. This was recently disabled

- kvm-Disable-non-rhel-machine-types-pc-0.12-pc-0.11-pc-0..patch [bz#607263]

Hence any guests which happened to have that wouldn't work. IMHO this is NOTABUG.

Closed per comment #6