Improve pmap_change_attr() so that it is able to demote a large (2/4MB)

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

1 files changed, 4 insertions, 0 deletions

diff --git a/sys/i386/include/pmap.h b/sys/i386/include/pmap.h
index c90f947..54e8c20 100644
--- a/sys/i386/include/pmap.h
+++ b/sys/i386/include/pmap.h
@@ -81,6 +81,10 @@
 #define	PG_PROT		(PG_RW|PG_U)	/* all protection bits . */
 #define PG_N		(PG_NC_PWT|PG_NC_PCD)	/* Non-cacheable */
 
+/* Page level cache control fields used to determine the PAT type */
+#define PG_PDE_CACHE	(PG_PDE_PAT | PG_NC_PWT | PG_NC_PCD)
+#define PG_PTE_CACHE	(PG_PTE_PAT | PG_NC_PWT | PG_NC_PCD)
+
 /*
  * Promotion to a 2 or 4MB (PDE) page mapping requires that the corresponding
  * 4KB (PTE) page mappings have identical settings for the following fields: