From ee1990f3bbcb3247eca0059c0f1e71886f934da1 Mon Sep 17 00:00:00 2001
From: David du Colombier <0intro@gmail.com>
Date: Fri, 31 Jan 1992 00:00:00 +0000
Subject: [PATCH] Plan 9 from Bell Labs 1992-01-31

---
 pc/mmu.c       | 30 +++++++++++++++++-------------
 port/page.c    | 12 ++++++++----
 port/portdat.h | 10 ++++------
 port/sysproc.c |  2 +-
 4 files changed, 30 insertions(+), 24 deletions(-)

diff --git a/pc/mmu.c b/pc/mmu.c
index 8ae0718f1804b8648efd9d7c9f7f181bb75590dc..1850294392126fb0d31ebed1673826ba877b18de 100644
--- a/pc/mmu.c
+++ b/pc/mmu.c
@@ -183,9 +183,12 @@ mmugetpage(int clear)
 }
 
 /*
- *  Put all page map pages on the process's free list and
+ *  Put all bottom level page map pages on the process's free list and
  *  call mapstack to set up the prototype page map.  This
  *  effectively forgets all of the process's mappings.
+ *
+ *  Don't free the top level page.  Just zero the used entries.  This
+ *  avoids a 4k copy each flushmmu.
  */
 void
 flushmmu(void)
@@ -193,19 +196,20 @@ flushmmu(void)
 	int s;
 	Proc *p;
 	Page *pg;
+	ulong *top;
 
 	if(u == 0)
 		return;
 
 	p = u->p;
 	s = splhi();
-	if(p->mmutop){
-		p->mmutop->next = p->mmufree;
-		p->mmufree = p->mmutop;
-		for(pg = p->mmufree; pg->next; pg = pg->next)
-			;
-		pg->next = p->mmuused;
-		p->mmutop = 0;
+	if(p->mmutop && p->mmuused){
+		top = (ulong*)p->mmutop->va;
+		for(pg = p->mmuused; pg->next; pg = pg->next)
+			top[pg->daddr] = 0;
+		top[pg->daddr] = 0;
+		pg->next = p->mmufree;
+		p->mmufree = p->mmuused;
 		p->mmuused = 0;
 	}
 	mapstack(u->p);
@@ -227,15 +231,14 @@ mapstack(Proc *p)
 	if(p->upage->va != (USERADDR|(p->pid&0xFFFF)) && p->pid != 0)
 		panic("mapstack %d 0x%lux 0x%lux", p->pid, p->upage->pa, p->upage->va);
 
-	if(p->mmutop)
-		pg = p->mmutop;
-	else
-		pg = &ktoppg;
-
 	/* map in u area */
 	upt[0] = PPN(p->upage->pa) | PTEVALID | PTEKERNEL | PTEWRITE;
 
 	/* tell processor about new page table (flushes cached entries) */
+	if(p->mmutop)
+		pg = p->mmutop;
+	else
+		pg = &ktoppg;
 	putcr3(pg->pa);
 
 	u = (User*)USERADDR;
@@ -322,6 +325,7 @@ putmmu(ulong va, ulong pa, Page *pg)
 		top[topoff] = PPN(pg->pa) | PTEVALID | PTEUSER | PTEWRITE;
 		pg->next = p->mmuused;
 		p->mmuused = pg;
+		pg->daddr = topoff;
 	}
 
 	/*
diff --git a/port/page.c b/port/page.c
index 869957593b1d551f63dd1e4ca7e02058409e7de0..0edc2ee7b133f61eebf5464e0024fbd764772d96 100644
--- a/port/page.c
+++ b/port/page.c
@@ -461,7 +461,7 @@ ptealloc(void)
 	while(ptealloclk.free == 0) {
 		unlock(&ptealloclk);
 
-		k = kmap(newpage(0, 0, 0));
+		k = kmap(newpage(1, 0, 0));
 		new = (Pte*)VA(k);
 		n = (BY2PG/sizeof(Pte))-1;
 		for(i = 0; i < n; i++)
@@ -476,9 +476,9 @@ ptealloc(void)
 	new = ptealloclk.free;
 	ptealloclk.free = new->next;
 	unlock(&ptealloclk);
-	memset(new->pages, 0, sizeof(new->pages));
 	new->first = &new->pages[PTEPERTAB];
 	new->last = new->pages;
+
 	return new;
 }
 
@@ -491,13 +491,17 @@ freepte(Segment *s, Pte *p)
 	case SG_PHYSICAL:
 		ptop = &p->pages[PTEPERTAB];
 		for(pg = p->pages; pg < ptop; pg++)
-			if(*pg)
+			if(*pg) {
 				(*s->pgfree)(*pg);
+				*pg = 0;
+			}
 		break;
 	default:
 		for(pg = p->first; pg <= p->last; pg++)
-			if(*pg)
+			if(*pg) {
 				putpage(*pg);
+				*pg = 0;
+			}
 	}
 
 	lock(&ptealloclk);
diff --git a/port/portdat.h b/port/portdat.h
index 95cd8e554394285482837c2b819286b0a5acdb80..2d22822166ac41788354aefef3b72adb7de2e902 100644
--- a/port/portdat.h
+++ b/port/portdat.h
@@ -327,12 +327,10 @@ struct Image
 
 struct Pte
 {
-	union {
-		Pte	*next;			/* Free list */
-		Page	*pages[PTEPERTAB];	/* Page map for this chunk of pte */
-	};
-	Page	**first;			/* First used entry */
-	Page	**last;				/* Last used entry */
+	Page	*pages[PTEPERTAB];	/* Page map for this chunk of pte */
+	Page	**first;		/* First used entry */
+	Page	**last;			/* Last used entry */
+	Pte	*next;			/* Free list */
 };
 
 /* Segment types */
diff --git a/port/sysproc.c b/port/sysproc.c
index 0dae5f278f54af37212a58ead064441f7e74e5e3..752c4705e79f2d3b0ce8c3dcba804e414c81de73 100644
--- a/port/sysproc.c
+++ b/port/sysproc.c
@@ -49,7 +49,7 @@ rfork(ulong flag)
 	p = newproc();
 
 	/* Page va of upage used as check in mapstack */
-	p->upage = newpage(1, 0, USERADDR|(p->pid&0xFFFF));
+	p->upage = newpage(0, 0, USERADDR|(p->pid&0xFFFF));
 	k = kmap(p->upage);
 	upa = VA(k);