From a5fa48bc2f70104f154998bd49e8b7e465957ab5 Mon Sep 17 00:00:00 2001
From: Bahadir Balban <bahadir@bahadir-laptop.(none)>
Date: Mon, 1 Sep 2008 17:26:49 +0300
Subject: [PATCH] When copying page tables, added excluding common kernel
 entries.

Normally common kernel entries in 2nd level page table need not get
copied to new tasks since those entries will be used commonly by all tasks.
On fork, we were copying those unnecessarily.
---
 src/arch/arm/v5/mm.c | 26 ++++++++++++++++++++++----
 1 file changed, 22 insertions(+), 4 deletions(-)

diff --git a/src/arch/arm/v5/mm.c b/src/arch/arm/v5/mm.c
index 8811fa9..e199eb7 100644
--- a/src/arch/arm/v5/mm.c
+++ b/src/arch/arm/v5/mm.c
@@ -359,6 +359,23 @@ void remove_mapping(unsigned long vaddr)
 	remove_mapping_pgd(vaddr, current->pgd);
 }
 
+/*
+ * Tell if a pgd index is a common kernel index. This is used to distinguish
+ * common kernel entries in a pgd, when copying page tables.
+ */
+int is_kern_pgdi(int i)
+{
+	if ((i >= PGD_INDEX(KERNEL_AREA_START) && i < PGD_INDEX(KERNEL_AREA_END)) ||
+	    (i >= PGD_INDEX(IO_AREA_START) && i < PGD_INDEX(IO_AREA_END)) ||
+	    (i == PGD_INDEX(USER_KIP_PAGE)) ||
+	    (i == PGD_INDEX(ARM_HIGH_VECTOR)) ||
+	    (i == PGD_INDEX(ARM_SYSCALL_VECTOR)) ||
+	    (i == PGD_INDEX(USERSPACE_UART_BASE)))
+		return 1;
+	else
+		return 0;
+}
+
 /*
  * Allocates and copies all levels of page tables from one task to another.
  * Useful when forking.
@@ -368,14 +385,15 @@ pgd_table_t *copy_page_tables(pgd_table_t *from)
 	pmd_table_t *pmd, *orig;
 	pgd_table_t *pgd;
 
-	/* Allocate and copy pgd */
+	/* Allocate and copy pgd. This includes all kernel entries */
 	pgd = alloc_pgd();
 	memcpy(pgd, from, sizeof(pgd_table_t));
 
-	/* Allocate and copy all valid pmds */
+	/* Allocate and copy all pmds that will be exclusive to new task. */
 	for (int i = 0; i < PGD_ENTRY_TOTAL; i++) {
-		/* Detect a pmd entry in original pgd? */
-		if ((pgd->entry[i] & PGD_TYPE_MASK) == PGD_TYPE_COARSE) {
+		/* Detect a pmd entry that is not a kernel pmd? */
+		if (!is_kern_pgdi(i) &&
+		    ((pgd->entry[i] & PGD_TYPE_MASK) == PGD_TYPE_COARSE)) {
 			/* Allocate new pmd */
 			pmd = alloc_pmd();