Qubes R4.1.2 (QSB #37 (XSA-254, Meltdown & Spectre) and Xen page-table isolation (XPTI)

What is the best way to mitigate the above vulnerability? Which virtualization mode is best protected from
Spectre and Meltdown? PVH or HVM? Does HVM result in the creation of vulnerable PV stub domains?

Has XPTI been implemented in Qubes R4.1.2? In accordance with the following article: