We needed to revert
Author: Igor Mammedov <firstname.lastname@example.org>
Date: Thu Dec 1 17:11:00 2011 -0500
[virt] xen: mask MTRR feature from guest BZ#750758
at the last minute to support kdump for xen hvm guests. We should try and bring it back (while keeping kdump working).
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I'm not sure we want to post this again (maybe not worth it), but Igor has hardware to test with, so assigning to him.