http://social.technet.microsoft.com/wiki/contents/articles/15576.hyper-v-update-list-for-windows-server-2012.aspx

The latest Hyper-V service packs, updates, and hotfixes for Windows Server 2012 are listed here in chronological order.

Applies To: Windows Server 2012

These updates and hotfixes can help avoid some known issues and may save you a support call.
A hotfix is intended to correct only the problem that is described in the article. You should not apply the hotfix if you have not seen the symptoms.

Note:A catch 22, do you install it to try preventing the problem from occurring or do you only install it if you see the problem and have an outage?

Note: Some updates are required only under certain circumstances, as noted in the table.

Note: On this link you can find a tool to help you identify which hotfixes and updates are installed and missing:
http://www.hyper-v.nu/archives/hvredevoort/2013/06/updated-windows-server-2012-hyper-v-and-cluster-hotfixes-and-updates/