I'm in the #kvm channel on freenode and have been experiencing the same issue. I thought it was virtio-blk (disk). I was told there was a patch submitted to trunk on Feb 8 to kvm. Here is the information I gathered from mjt.
Issue described: http://www.mail-archive.com/kvm@vger.../msg26033.html
Issue patched: http://marc.info/?l=kvm&m=126564542625725&w=2
here is the conversation I had on irc http://pastebin.com/ZX4pVmZB
here is the git comment: 06b1297017415ae6a07a0e97ad7d8e90b2d95823
it is patched in qemu-kvm 0.12.3
Issue described: http://www.mail-archive.com/kvm@vger.../msg26033.html
Issue patched: http://marc.info/?l=kvm&m=126564542625725&w=2
here is the conversation I had on irc http://pastebin.com/ZX4pVmZB
here is the git comment: 06b1297017415ae6a07a0e97ad7d8e90b2d95823
it is patched in qemu-kvm 0.12.3