Add config option PAE_TABLES for the i386 kernel. It switches pmap to

use PAE format for the page tables, but does not incur other
consequences of the full PAE config.  In particular, vm_paddr_t and
bus_addr_t are left 32bit, and max supported memory is still limited
by 4GB.

The option allows to have nx permissions for memory mappings on i386
kernel, while keeping the usual i386 KBI and avoiding the kernel data
sizing problems typical for the PAE config.

Intel documented that the PAE format for page tables is available
starting with the Pentium Pro, but it is possible that the plain
Pentium CPUs have the required support (Appendix H).  The goal is to
enable the option and non-exec mappings on i386 for the GENERIC
kernel.  Anybody wanting a useful system on 486, have to reconfigure
the modern i386 kernel anyway.

Discussed with:	alc, jhb
Sponsored by:	The FreeBSD Foundation
MFC after:	2 weeks

1 files changed, 13 insertions, 10 deletions

diff --git a/sys/i386/include/pmap.h b/sys/i386/include/pmap.h
index 2c9a409..0d8057f 100644
--- a/sys/i386/include/pmap.h
+++ b/sys/i386/include/pmap.h
@@ -63,7 +63,7 @@
 #define	PG_AVAIL2	0x400	/*   <	programmers use		*/
 #define	PG_AVAIL3	0x800	/*    \				*/
 #define	PG_PDE_PAT	0x1000	/* PAT	PAT index		*/
-#ifdef PAE
+#if defined(PAE) || defined(PAE_TABLES)
 #define	PG_NX		(1ull<<63) /* No-execute */
 #endif
 
@@ -71,7 +71,7 @@
 /* Our various interpretations of the above */
 #define PG_W		PG_AVAIL1	/* "Wired" pseudoflag */
 #define	PG_MANAGED	PG_AVAIL2
-#ifdef PAE
+#if defined(PAE) || defined(PAE_TABLES)
 #define	PG_FRAME	(0x000ffffffffff000ull)
 #define	PG_PS_FRAME	(0x000fffffffe00000ull)
 #else
@@ -110,7 +110,7 @@
  * is 1 Gigabyte.  Double everything.  It must be a multiple of 8 for PAE.
  */
 #ifndef KVA_PAGES
-#ifdef PAE
+#if defined(PAE) || defined(PAE_TABLES)
 #define KVA_PAGES	512
 #else
 #define KVA_PAGES	256
@@ -128,11 +128,14 @@
  * be calculated as follows:
  *     max_phys / PAGE_SIZE * sizeof(struct vm_page) / NBPDR
  * PAE:      max_phys 16G, sizeof(vm_page) 76, NBPDR 2M, 152 page table pages.
+ * PAE_TABLES: max_phys 4G,  sizeof(vm_page) 68, NBPDR 2M, 36 page table pages.
  * Non-PAE:  max_phys 4G,  sizeof(vm_page) 68, NBPDR 4M, 18 page table pages.
  */
 #ifndef NKPT
-#ifdef PAE
+#if defined(PAE)
 #define	NKPT		240
+#elif defined(PAE_TABLES)
+#define	NKPT		60
 #else
 #define	NKPT		30
 #endif
@@ -166,7 +169,7 @@
 
 #include <vm/_vm_radix.h>
 
-#ifdef PAE
+#if defined(PAE) || defined(PAE_TABLES)
 
 typedef uint64_t pdpt_entry_t;
 typedef uint64_t pd_entry_t;
@@ -193,7 +196,7 @@ extern pt_entry_t PTmap[];
 extern pd_entry_t PTD[];
 extern pd_entry_t PTDpde[];
 
-#ifdef PAE
+#if defined(PAE) || defined(PAE_TABLES)
 extern pdpt_entry_t *IdlePDPT;
 #endif
 extern pd_entry_t *IdlePTD;	/* physical address of "Idle" state directory */
@@ -331,7 +334,7 @@ pmap_kextract(vm_offset_t va)
 #define PT_UPDATES_FLUSH()
 #endif
 
-#if defined(PAE) && !defined(XEN)
+#if (defined(PAE) || defined(PAE_TABLES)) && !defined(XEN)
 
 #define	pde_cmpset(pdep, old, new)	atomic_cmpset_64_i586(pdep, old, new)
 #define	pte_load_store(ptep, pte)	atomic_swap_64_i586(ptep, pte)
@@ -340,7 +343,7 @@ pmap_kextract(vm_offset_t va)
 
 extern pt_entry_t pg_nx;
 
-#elif !defined(PAE) && !defined(XEN)
+#elif !defined(PAE) && !defined(PAE_TABLES) && !defined(XEN)
 
 #define	pde_cmpset(pdep, old, new)	atomic_cmpset_int(pdep, old, new)
 #define	pte_load_store(ptep, pte)	atomic_swap_int(ptep, pte)
@@ -375,8 +378,8 @@ struct pmap {
 	cpuset_t		pm_active;	/* active on cpus */
 	struct pmap_statistics	pm_stats;	/* pmap statistics */
 	LIST_ENTRY(pmap) 	pm_list;	/* List of all pmaps */
-#ifdef PAE
-	pdpt_entry_t		*pm_pdpt;	/* KVA of page director pointer
+#if defined(PAE) || defined(PAE_TABLES)
+	pdpt_entry_t		*pm_pdpt;	/* KVA of page directory pointer
 						   table */
 #endif
 	struct vm_radix		pm_root;	/* spare page table pages */