svn commit: r214938 - head/sys/i386/i386

[Alan Cox]

Author: alc
Date: Sun Nov  7 18:42:37 2010
New Revision: 214938
URL: http://svn.freebsd.org/changeset/base/214938

Log:
  Eliminate a possible race between pmap_pinit() and pmap_kenter_pde() on
  superpage promotion or demotion.
  
  Micro-optimize pmap_kenter_pde().
  
  Reviewed by:	kib, jhb (an earlier version)
  MFC after:	1 week

Modified:
  head/sys/i386/i386/pmap.c

Modified: head/sys/i386/i386/pmap.c
==============================================================================
--- head/sys/i386/i386/pmap.c	Sun Nov  7 18:25:42 2010	(r214937)
+++ head/sys/i386/i386/pmap.c	Sun Nov  7 18:42:37 2010	(r214938)
@@ -1678,11 +1678,19 @@ pmap_unuse_pt(pmap_t pmap, vm_offset_t v
 	return (pmap_unwire_pte_hold(pmap, mpte, free));
 }
 
+/*
+ * Initialize the pmap for the swapper process.
+ */
 void
 pmap_pinit0(pmap_t pmap)
 {
 
 	PMAP_LOCK_INIT(pmap);
+	/*
+	 * Since the page table directory is shared with the kernel pmap,
+	 * which is already included in the list "allpmaps", this pmap does
+	 * not need to be inserted into that list.
+	 */
 	pmap->pm_pdir = (pd_entry_t *)(KERNBASE + (vm_offset_t)IdlePTD);
 #ifdef PAE
 	pmap->pm_pdpt = (pdpt_entry_t *)(KERNBASE + (vm_offset_t)IdlePDPT);
@@ -1692,9 +1700,6 @@ pmap_pinit0(pmap_t pmap)
 	PCPU_SET(curpmap, pmap);
 	TAILQ_INIT(&pmap->pm_pvchunk);
 	bzero(&pmap->pm_stats, sizeof pmap->pm_stats);
-	mtx_lock_spin(&allpmaps_lock);
-	LIST_INSERT_HEAD(&allpmaps, pmap, pm_list);
-	mtx_unlock_spin(&allpmaps_lock);
 }
 
 /*
@@ -1759,9 +1764,9 @@ pmap_pinit(pmap_t pmap)
 
 	mtx_lock_spin(&allpmaps_lock);
 	LIST_INSERT_HEAD(&allpmaps, pmap, pm_list);
-	mtx_unlock_spin(&allpmaps_lock);
-	/* Wire in kernel global address entries. */
+	/* Copy the kernel page table directory entries. */
 	bcopy(PTD + KPTDI, pmap->pm_pdir + KPTDI, nkpt * sizeof(pd_entry_t));
+	mtx_unlock_spin(&allpmaps_lock);
 
 	/* install self-referential address mapping entry(s) */
 	for (i = 0; i < NPGPTD; i++) {