Security update for xen (important)

This update for xen fixes the following security issues:

• CVE-2015-8550: paravirtualized drivers incautious about shared memory
  contents (XSA-155, boo#957988)
• CVE-2015-8558: qemu: usb: infinite loop in ehci_advance_state results in
  DoS (boo#959006)
• CVE-2015-7549: qemu pci: null pointer dereference issue (boo#958918)
• CVE-2015-8504: qemu: ui: vnc: avoid floating point exception (boo#958493)
• CVE-2015-8554: qemu-dm buffer overrun in MSI-X handling (XSA-164,
  boo#958007)
• CVE-2015-8555: information leak in legacy x86 FPU/XMM initialization
  (XSA-165, boo#958009)
• boo#958523 xen: ioreq handling possibly susceptible to multiple read
  issue (XSA-166)
• CVE-2015-8345: xen: qemu: net: eepro100: infinite loop in processing
  command block list (boo#956832)
• boo#956592: xen: virtual PMU is unsupported (XSA-163)
• CVE-2015-8339, CVE-2015-8340: xen: XENMEM_exchange error handling issues
  (XSA-159, boo#956408)
• CVE-2015-8341: xen: libxl leak of pv kernel and initrd on error
  (XSA-160, boo#956409)
• CVE-2015-7504: xen: heap buffer overflow vulnerability in pcnet emulator
  (XSA-162, boo#956411)
• CVE-2015-7311: xen: libxl fails to honour readonly flag on disks with
  qemu-xen (xsa-142, boo#947165)
• CVE-2015-8104: Xen: guest to host DoS by triggering an infinite loop in
  microcode via #DB exception (boo#954405)
• CVE-2015-5307: xen: x86: CPU lockup during fault delivery (XSA-156,
  boo#954018)
• CVE-2015-7970: xen: x86: Long latency populate-on-demand operation is
  not preemptible (XSA-150, boo#950704)