From 971238ae4833b351a7eeed8e812fce88553c0e6a Mon Sep 17 00:00:00 2001
From: Alan Cox <alc@FreeBSD.org>
Date: Tue, 20 Dec 2011 20:16:12 +0000
Subject: [PATCH] The Xen pmap doesn't support superpages.  So, there is no
 point in it initializing structures, like the pv table, that are only used to
 implement superpages.  In fact, some of the unnecessary code in pmap_init()
 was actually doing harm.  It was preventing the kernel from booting on
 virtual machines with more than 768 MB of memory.

Tested by:	sbruno
---
 sys/i386/xen/pmap.c | 53 ++-------------------------------------------
 1 file changed, 2 insertions(+), 51 deletions(-)

diff --git a/sys/i386/xen/pmap.c b/sys/i386/xen/pmap.c
index c81834be67f9..5468520c249b 100644
--- a/sys/i386/xen/pmap.c
+++ b/sys/i386/xen/pmap.c
@@ -184,9 +184,6 @@ __FBSDID("$FreeBSD$");
 #define PV_STAT(x)	do { } while (0)
 #endif
 
-#define	pa_index(pa)	((pa) >> PDRSHIFT)
-#define	pa_to_pvh(pa)	(&pv_table[pa_index(pa)])
-
 /*
  * Get PDEs and PTEs for user/kernel address space
  */
@@ -230,7 +227,6 @@ static int pat_works;			/* Is page attribute table sane? */
  * Data for the pv entry allocation mechanism
  */
 static int pv_entry_count = 0, pv_entry_max = 0, pv_entry_high_water = 0;
-static struct md_page *pv_table;
 static int shpgperproc = PMAP_SHPGPERPROC;
 
 struct pv_chunk *pv_chunkbase;		/* KVA block for pv_chunks */
@@ -278,9 +274,6 @@ SYSCTL_INT(_debug, OID_AUTO, PMAP1unchanged, CTLFLAG_RD,
 static struct mtx PMAP2mutex;
 
 static SYSCTL_NODE(_vm, OID_AUTO, pmap, CTLFLAG_RD, 0, "VM/pmap parameters");
-static int pg_ps_enabled;
-SYSCTL_INT(_vm_pmap, OID_AUTO, pg_ps_enabled, CTLFLAG_RDTUN, &pg_ps_enabled, 0,
-    "Are large page mappings enabled?");
 
 SYSCTL_INT(_vm_pmap, OID_AUTO, pv_entry_max, CTLFLAG_RD, &pv_entry_max, 0,
 	"Max number of PV entries");
@@ -636,24 +629,8 @@ pmap_ptelist_init(vm_offset_t *head, void *base, int npages)
 void
 pmap_init(void)
 {
-	vm_page_t mpte;
-	vm_size_t s;
-	int i, pv_npg;
 
 	/*
-	 * Initialize the vm page array entries for the kernel pmap's
-	 * page table pages.
-	 */ 
-	for (i = 0; i < nkpt; i++) {
-		mpte = PHYS_TO_VM_PAGE(xpmap_mtop(PTD[i + KPTDI] & PG_FRAME));
-		KASSERT(mpte >= vm_page_array &&
-		    mpte < &vm_page_array[vm_page_array_size],
-		    ("pmap_init: page table page is out of range"));
-		mpte->pindex = i + KPTDI;
-		mpte->phys_addr = xpmap_mtop(PTD[i + KPTDI] & PG_FRAME);
-	}
-
-        /*
 	 * Initialize the address space (zone) for the pv entries.  Set a
 	 * high water mark so that the system can recover from excessive
 	 * numbers of pv entries.
@@ -664,26 +641,6 @@ pmap_init(void)
 	pv_entry_max = roundup(pv_entry_max, _NPCPV);
 	pv_entry_high_water = 9 * (pv_entry_max / 10);
 
-	/*
-	 * Are large page mappings enabled?
-	 */
-	TUNABLE_INT_FETCH("vm.pmap.pg_ps_enabled", &pg_ps_enabled);
-
-	/*
-	 * Calculate the size of the pv head table for superpages.
-	 */
-	for (i = 0; phys_avail[i + 1]; i += 2);
-	pv_npg = round_4mpage(phys_avail[(i - 2) + 1]) / NBPDR;
-
-	/*
-	 * Allocate memory for the pv head table for superpages.
-	 */
-	s = (vm_size_t)(pv_npg * sizeof(struct md_page));
-	s = round_page(s);
-	pv_table = (struct md_page *)kmem_alloc(kernel_map, s);
-	for (i = 0; i < pv_npg; i++)
-		TAILQ_INIT(&pv_table[i].pv_list);
-
 	pv_maxchunks = MAX(pv_entry_max / _NPCPV, maxproc);
 	pv_chunkbase = (struct pv_chunk *)kmem_alloc_nofault(kernel_map,
 	    PAGE_SIZE * pv_maxchunks);
@@ -3448,21 +3405,15 @@ pmap_page_wired_mappings(vm_page_t m)
 }
 
 /*
- * Returns TRUE if the given page is mapped individually or as part of
- * a 4mpage.  Otherwise, returns FALSE.
+ * Returns TRUE if the given page is mapped.  Otherwise, returns FALSE.
  */
 boolean_t
 pmap_page_is_mapped(vm_page_t m)
 {
-	boolean_t rv;
 
 	if ((m->oflags & VPO_UNMANAGED) != 0)
 		return (FALSE);
-	vm_page_lock_queues();
-	rv = !TAILQ_EMPTY(&m->md.pv_list) ||
-	    !TAILQ_EMPTY(&pa_to_pvh(VM_PAGE_TO_PHYS(m))->pv_list);
-	vm_page_unlock_queues();
-	return (rv);
+	return (!TAILQ_EMPTY(&m->md.pv_list));
 }
 
 /*