Xen 4.12 just landed

[olivierlambert]

https://xenproject.org/2019/04/02/whats-new-in-xen-4-12/

In short:

• 1446 commits from 364 patches
• possibility to build for PV or HVM/PVH only (reducing attack surface)
• QEMU deprivilege (also reducing attack surface)
• Argo (new inter-domain communication, @ronan-a will take a look)
• Improved VM introspection (less overhead)
• Credit 2 schedule by default
• PVH dom0 in tech preview
• Better IOMMU mapping for improved EPYC boot time
• auto dom0 sizing (% of total system RAM or static+percent)

Details: https://wiki.xenproject.org/wiki/Xen_Project_4.12_Feature_List