Author: alc
Date: Fri Aug 17 05:02:29 2012
New Revision: 239352
URL: http://svn.freebsd.org/changeset/base/239352
Log:
Fix two problems with pmap_clear_modify().
First, pmap_clear_modify() is write protecting all mappings to the specified
page, not just clearing the modified bit. Specifically, it sets PTE_RO on
the PTE, which is wrong. Moreover, it is calling vm_page_dirty(), which is
not the expected behavior for pmap_clear_modify(). Generally speaking, the
machine-independent VM layer masks these mistakes. For example, setting
PTE_RO will result in additional soft faults, but not a catastrophe.
Second, pmap_clear_modify() may not clear the modified bits because it only
iterates over the PV list when the page has the PV_TABLE_MOD flag set and
elsewhere the pmap clears the PV_TABLE_MOD flag anytime a modified mapping
is write protected or destroyed. However, the page may still have other
mappings with the modified bit set.
Eliminate a stale comment.
Modified:
head/sys/mips/mips/pmap.c
Modified: head/sys/mips/mips/pmap.c
==============================================================================
--- head/sys/mips/mips/pmap.c Fri Aug 17 04:44:57 2012 (r239351)
+++ head/sys/mips/mips/pmap.c Fri Aug 17 05:02:29 2012 (r239352)
@@ -179,7 +179,6 @@ static vm_page_t pmap_pv_reclaim(pmap_t
static void pmap_pvh_free(struct md_page *pvh, pmap_t pmap, vm_offset_t va);
static pv_entry_t pmap_pvh_remove(struct md_page *pvh, pmap_t pmap,
vm_offset_t va);
-static __inline void pmap_changebit(vm_page_t m, int bit, boolean_t setem);
static vm_page_t pmap_enter_quick_locked(pmap_t pmap, vm_offset_t va,
vm_page_t m, vm_prot_t prot, vm_page_t mpte);
static int pmap_remove_pte(struct pmap *pmap, pt_entry_t *ptq, vm_offset_t va,
@@ -2664,8 +2663,6 @@ pmap_remove_pages(pmap_t pmap)
/*
* pmap_testbit tests bits in pte's
- * note that the testbit/changebit routines are inline,
- * and a lot of things compile-time evaluate.
*/
static boolean_t
pmap_testbit(vm_page_t m, int bit)
@@ -2692,51 +2689,6 @@ pmap_testbit(vm_page_t m, int bit)
}
/*
- * this routine is used to clear dirty bits in ptes
- */
-static __inline void
-pmap_changebit(vm_page_t m, int bit, boolean_t setem)
-{
- pv_entry_t pv;
- pmap_t pmap;
- pt_entry_t *pte;
-
- if (m->oflags & VPO_UNMANAGED)
- return;
-
- rw_assert(&pvh_global_lock, RA_WLOCKED);
- /*
- * Loop over all current mappings setting/clearing as appropos If
- * setting RO do we need to clear the VAC?
- */
- TAILQ_FOREACH(pv, &m->md.pv_list, pv_list) {
- pmap = PV_PMAP(pv);
- PMAP_LOCK(pmap);
- pte = pmap_pte(pmap, pv->pv_va);
- if (setem) {
- *pte |= bit;
- pmap_update_page(pmap, pv->pv_va, *pte);
- } else {
- pt_entry_t pbits = *pte;
-
- if (pbits & bit) {
- if (bit == PTE_D) {
- if (pbits & PTE_D)
- vm_page_dirty(m);
- *pte = (pbits & ~PTE_D) | PTE_RO;
- } else {
- *pte = pbits & ~bit;
- }
- pmap_update_page(pmap, pv->pv_va, *pte);
- }
- }
- PMAP_UNLOCK(pmap);
- }
- if (!setem && bit == PTE_D)
- vm_page_aflag_clear(m, PGA_WRITEABLE);
-}
-
-/*
* pmap_page_wired_mappings:
*
* Return the number of managed mappings to the given physical page
@@ -2896,6 +2848,9 @@ pmap_is_prefaultable(pmap_t pmap, vm_off
void
pmap_clear_modify(vm_page_t m)
{
+ pmap_t pmap;
+ pt_entry_t *pte;
+ pv_entry_t pv;
KASSERT((m->oflags & VPO_UNMANAGED) == 0,
("pmap_clear_modify: page %p is not managed", m));
@@ -2911,10 +2866,17 @@ pmap_clear_modify(vm_page_t m)
if ((m->aflags & PGA_WRITEABLE) == 0)
return;
rw_wlock(&pvh_global_lock);
- if (m->md.pv_flags & PV_TABLE_MOD) {
- pmap_changebit(m, PTE_D, FALSE);
- m->md.pv_flags &= ~PV_TABLE_MOD;
+ TAILQ_FOREACH(pv, &m->md.pv_list, pv_list) {
+ pmap = PV_PMAP(pv);
+ PMAP_LOCK(pmap);
+ pte = pmap_pte(pmap, pv->pv_va);
+ if (pte_test(pte, PTE_D)) {
+ pte_clear(pte, PTE_D);
+ pmap_update_page(pmap, pv->pv_va, *pte);
+ }
+ PMAP_UNLOCK(pmap);
}
+ m->md.pv_flags &= ~PV_TABLE_MOD;
rw_wunlock(&pvh_global_lock);
}
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