1. Introduce a new function make_migration_entry() to
isolate common code between copy_pte_range and change_pte_range.
2. Modify change_pte_range() to check for a migration entry.
If a write migration entry is found and there is a request for
a READ permissions then change the migration entry.
I am a bit concerned about the check of newprot. Are there other
values than PAGE_READONLY that indicate read only access?
Signed-off-by: Christoph Lameter <[email protected]>
Index: linux-2.6.17-rc1-mm3/mm/memory.c
===================================================================
--- linux-2.6.17-rc1-mm3.orig/mm/memory.c 2006-04-18 11:09:23.252982000 -0700
+++ linux-2.6.17-rc1-mm3/mm/memory.c 2006-04-20 12:22:50.626800376 -0700
@@ -447,14 +447,11 @@
}
if (is_migration_entry(entry) &&
is_cow_mapping(vm_flags)) {
- page = migration_entry_to_page(entry);
-
/*
* COW mappings require pages in both parent
- * and child to be set to read.
+ * and child to be set to read.
*/
- entry = make_migration_entry(page,
- SWP_MIGRATION_READ);
+ make_migration_entry_read(&entry);
pte = swp_entry_to_pte(entry);
set_pte_at(src_mm, addr, src_pte, pte);
}
Index: linux-2.6.17-rc1-mm3/mm/mprotect.c
===================================================================
--- linux-2.6.17-rc1-mm3.orig/mm/mprotect.c 2006-04-18 11:12:30.614603000 -0700
+++ linux-2.6.17-rc1-mm3/mm/mprotect.c 2006-04-20 12:17:03.771210036 -0700
@@ -19,6 +19,8 @@
#include <linux/mempolicy.h>
#include <linux/personality.h>
#include <linux/syscalls.h>
+#include <linux/swap.h>
+#include <linux/swapops.h>
#include <asm/uaccess.h>
#include <asm/pgtable.h>
@@ -28,22 +30,35 @@
static void change_pte_range(struct mm_struct *mm, pmd_t *pmd,
unsigned long addr, unsigned long end, pgprot_t newprot)
{
- pte_t *pte;
+ pte_t *pte, oldpte;
spinlock_t *ptl;
pte = pte_offset_map_lock(mm, pmd, addr, &ptl);
do {
- if (pte_present(*pte)) {
+ oldpte = *pte;
+ if (pte_present(oldpte)) {
pte_t ptent;
/* Avoid an SMP race with hardware updated dirty/clean
* bits by wiping the pte and then setting the new pte
* into place.
*/
- ptent = pte_modify(ptep_get_and_clear(mm, addr, pte), newprot);
+ ptent = pte_modify(ptep_get_and_clear(mm, addr, pte),
+ newprot);
set_pte_at(mm, addr, pte, ptent);
lazy_mmu_prot_update(ptent);
+ } else
+ if (!pte_file(oldpte) && pgprot_val(newprot) ==
+ pgprot_val(PAGE_READONLY)) {
+ swp_entry_t entry = pte_to_swp_entry(oldpte);
+
+ if (is_write_migration_entry(entry)) {
+ make_migration_entry_read(&entry);
+ set_pte_at(mm, addr, pte,
+ swp_entry_to_pte(entry));
+ }
}
+
} while (pte++, addr += PAGE_SIZE, addr != end);
pte_unmap_unlock(pte - 1, ptl);
}
Index: linux-2.6.17-rc1-mm3/include/linux/swapops.h
===================================================================
--- linux-2.6.17-rc1-mm3.orig/include/linux/swapops.h 2006-04-18 10:58:33.675573000 -0700
+++ linux-2.6.17-rc1-mm3/include/linux/swapops.h 2006-04-20 12:00:29.279539838 -0700
@@ -98,6 +98,11 @@
return p;
}
+static inline void make_migration_entry_read(swp_entry_t *entry)
+{
+ *entry = swp_entry(SWP_MIGRATION_READ, swp_offset(*entry));
+}
+
extern void migration_entry_wait(struct mm_struct *mm, pmd_t *pmd,
unsigned long address);
#else
@@ -105,6 +110,7 @@
#define make_migration_entry(page, write) swp_entry(0, 0)
#define is_migration_entry(swp) 0
#define migration_entry_to_page(swp) NULL
+static inline void make_migration_entry_read(entryp) { }
static inline void migration_entry_wait(struct mm_struct *mm, pmd_t *pmd,
unsigned long address) { }
-
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