The Svpbmt extension provides specification of "Page-Based Memory
Types", or memory attributes (e.g. cacheability constraints).
Extend pmap code to apply memory attributes when creating/updating PTEs.
This is done in a way which should be non-hostile to CPUs lacking memory
attribute (Svpbmt) support, and applicable to alternate encodings of
this feature (T-HEAD CPUs, see next review).
This still needs some work, but this initial sketch handles most of the
changes required to support this feature.
TODO:
- update DMAP entries
- split vm.pmap.kernel_maps code into separate commit (?)
- further testing