This update for xen fixes the following security issues:
- CVE-2018-3646: Systems with microprocessors utilizing speculative execution and address translations may have allowed unauthorized disclosure of information residing in the L1 data cache to an attacker with local user access with guest OS privilege via a terminal page fault and a side-channel analysis (bsc#1091107, bsc#1027519). - Incorrect MSR_DEBUGCTL handling let guests enable BTS allowing a malicious or buggy guest administrator can lock up the entire host (bsc#1103276)