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Subject[PATCH 2.5.42-mm3] Fix mremap for shared page tables

Hugh Dickens was right. mremap was broken wrt shared page tables. Here's
the fix.

Dave McCracken

======================================================================
Dave McCracken IBM Linux Base Kernel Team 1-512-838-3059
dmccr@us.ibm.com T/L 678-3059
--- 2.5.42-mm3-shsent/mm/mremap.c 2002-10-15 09:59:37.000000000 -0500
+++ 2.5.42-mm3-shpte/mm/mremap.c 2002-10-15 17:16:59.000000000 -0500
@@ -15,6 +15,7 @@
#include <linux/swap.h>
#include <linux/fs.h>
#include <linux/highmem.h>
+#include <linux/rmap-locking.h>

#include <asm/uaccess.h>
#include <asm/pgalloc.h>
@@ -23,6 +24,7 @@

static pte_t *get_one_pte_map_nested(struct mm_struct *mm, unsigned long addr)
{
+ struct page *ptepage;
pgd_t * pgd;
pmd_t * pmd;
pte_t * pte = NULL;
@@ -45,8 +47,17 @@
goto end;
}

+ ptepage = pmd_page(*pmd);
+ pte_page_lock(ptepage);
+#ifdef CONFIG_SHAREPTE
+ if (page_count(ptepage) > 1) {
+ pte_unshare(mm, pmd, addr);
+ ptepage = pmd_page(*pmd);
+ }
+#endif
pte = pte_offset_map_nested(pmd, addr);
if (pte_none(*pte)) {
+ pte_page_unlock(ptepage);
pte_unmap_nested(pte);
pte = NULL;
}
@@ -54,6 +65,32 @@
return pte;
}

+static inline void drop_pte_nested(struct mm_struct *mm, unsigned long addr, pte_t *pte)
+{
+ struct page *ptepage;
+ pgd_t *pgd;
+ pmd_t *pmd;
+
+ pgd = pgd_offset(mm, addr);
+ pmd = pmd_offset(pgd, addr);
+ ptepage = pmd_page(*pmd);
+ pte_page_unlock(ptepage);
+ pte_unmap_nested(pte);
+}
+
+static inline void drop_pte(struct mm_struct *mm, unsigned long addr, pte_t *pte)
+{
+ struct page *ptepage;
+ pgd_t *pgd;
+ pmd_t *pmd;
+
+ pgd = pgd_offset(mm, addr);
+ pmd = pmd_offset(pgd, addr);
+ ptepage = pmd_page(*pmd);
+ pte_page_unlock(ptepage);
+ pte_unmap(pte);
+}
+
#ifdef CONFIG_HIGHPTE /* Save a few cycles on the sane machines */
static inline int page_table_present(struct mm_struct *mm, unsigned long addr)
{
@@ -72,12 +109,24 @@

static inline pte_t *alloc_one_pte_map(struct mm_struct *mm, unsigned long addr)
{
+ struct page *ptepage;
pmd_t * pmd;
pte_t * pte = NULL;

pmd = pmd_alloc(mm, pgd_offset(mm, addr), addr);
- if (pmd)
+ if (pmd) {
+ ptepage = pmd_page(*pmd);
+#ifdef CONFIG_SHAREPTE
+ pte_page_lock(ptepage);
+ if (page_count(ptepage) > 1) {
+ pte_unshare(mm, pmd, addr);
+ ptepage = pmd_page(*pmd);
+ }
+ pte_page_unlock(ptepage);
+#endif
pte = pte_alloc_map(mm, pmd, addr);
+ pte_page_lock(ptepage);
+ }
return pte;
}

@@ -121,15 +170,15 @@
* atomic kmap
*/
if (!page_table_present(mm, new_addr)) {
- pte_unmap_nested(src);
+ drop_pte_nested(mm, old_addr, src);
src = NULL;
}
dst = alloc_one_pte_map(mm, new_addr);
if (src == NULL)
src = get_one_pte_map_nested(mm, old_addr);
error = copy_one_pte(mm, src, dst);
- pte_unmap_nested(src);
- pte_unmap(dst);
+ drop_pte_nested(mm, old_addr, src);
+ drop_pte(mm, new_addr, dst);
}
flush_tlb_page(vma, old_addr);
spin_unlock(&mm->page_table_lock);
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