From d74e85dbb9aba51f1ffc63a0ebae250559a8fcd9 Mon Sep 17 00:00:00 2001
From: alc <alc@FreeBSD.org>
Date: Sun, 6 Jul 2014 17:42:38 +0000
Subject: Introduce pmap_unwire().  It will replace pmap_change_wiring(). 
 There are several reasons for this change:

pmap_change_wiring() has never (in my memory) been used to set the wired
attribute on a virtual page.  We have always used pmap_enter() to do that.
Moreover, it is not really safe to use pmap_change_wiring() to set the wired
attribute on a virtual page.  The description of pmap_change_wiring() says
that it assumes the existence of a mapping in the pmap.  However, non-wired
mappings may be reclaimed by the pmap at any time.  (See pmap_collect().)
Many implementations of pmap_change_wiring() will crash if the mapping does
not exist.

pmap_unwire() accepts a range of virtual addresses, whereas
pmap_change_wiring() acts upon a single virtual page.  Since we are
typically unwiring a range of virtual addresses, pmap_unwire() will be more
efficient.  Moreover, pmap_unwire() allows us to unwire superpage mappings.
Previously, we were forced to demote the superpage mapping, because
pmap_change_wiring() only allowed us to express the unwiring of a single
base page mapping at a time.  This added to the overhead of unwiring for
large ranges of addresses, including the implicit unwiring that occurs at
process termination.

Implementations for arm and powerpc will follow.

Discussed with:	jeff, marcel
Reviewed by:	kib
Sponsored by:	EMC / Isilon Storage Division
---
 sys/i386/xen/pmap.c | 51 +++++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 51 insertions(+)

(limited to 'sys/i386/xen/pmap.c')

diff --git a/sys/i386/xen/pmap.c b/sys/i386/xen/pmap.c
index fdc64bc..54ee3a6 100644
--- a/sys/i386/xen/pmap.c
+++ b/sys/i386/xen/pmap.c
@@ -3199,6 +3199,57 @@ pmap_change_wiring(pmap_t pmap, vm_offset_t va, boolean_t wired)
 	rw_wunlock(&pvh_global_lock);
 }
 
+/*
+ *	Clear the wired attribute from the mappings for the specified range of
+ *	addresses in the given pmap.  Every valid mapping within that range
+ *	must have the wired attribute set.  In contrast, invalid mappings
+ *	cannot have the wired attribute set, so they are ignored.
+ *
+ *	The wired attribute of the page table entry is not a hardware feature,
+ *	so there is no need to invalidate any TLB entries.
+ */
+void
+pmap_unwire(pmap_t pmap, vm_offset_t sva, vm_offset_t eva)
+{
+	vm_offset_t pdnxt;
+	pd_entry_t *pde;
+	pt_entry_t *pte;
+
+	CTR3(KTR_PMAP, "pmap_unwire: pmap=%p sva=0x%x eva=0x%x", pmap, sva,
+	    eva);
+	rw_wlock(&pvh_global_lock);
+	sched_pin();
+	PMAP_LOCK(pmap);
+	for (; sva < eva; sva = pdnxt) {
+		pdnxt = (sva + NBPDR) & ~PDRMASK;
+		if (pdnxt < sva)
+			pdnxt = eva;
+		pde = pmap_pde(pmap, sva);
+		if ((*pde & PG_V) == 0)
+			continue;
+		if ((*pde & PG_PS) != 0)
+			panic("pmap_unwire: unexpected PG_PS in pde %#jx",
+			    (uintmax_t)*pde);
+		if (pdnxt > eva)
+			pdnxt = eva;
+		for (pte = pmap_pte_quick(pmap, sva); sva != pdnxt; pte++,
+		    sva += PAGE_SIZE) {
+			if ((*pte & PG_V) == 0)
+				continue;
+			if ((*pte & PG_W) == 0)
+				panic("pmap_unwire: pte %#jx is missing PG_W",
+				    (uintmax_t)*pte);
+			PT_SET_VA_MA(pte, *pte & ~PG_W, FALSE);
+			pmap->pm_stats.wired_count--;
+		}
+	}
+	if (*PMAP1)
+		PT_CLEAR_VA(PMAP1, FALSE);
+	PT_UPDATES_FLUSH();
+	sched_unpin();
+	rw_wunlock(&pvh_global_lock);
+	PMAP_UNLOCK(pmap);
+}
 
 
 /*
-- 
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