page into 4KB pages as needed. This should be fairly rare in practice
on i386. This includes merging the following changes from the amd64 pmap:
180430, 180485, 180845, 181043, 181077, and 196318.
- Add basic support for changing attributes on PDEs to pmap_change_attr()
similar to the support in the initial version of pmap_change_attr() on
amd64 including inlines for pmap_pde_attr() and pmap_pte_attr().
- Extend pmap_demote_pde() to include the ability to instantiate a new page
table page where none existed before.
- Enhance pmap_change_attr(). Use pmap_demote_pde() to demote a 2/4MB page
mapping to 4KB page mappings when the specified attribute change only
applies to a portion of the 2/4MB page. Previously, in such cases,
pmap_change_attr() gave up and returned an error.
- Correct a critical accounting error in pmap_demote_pde().
Reviewed by: alc
MFC after: 3 days
d76071806c