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Subject[PATCH 14/21] mm: pte_offset_map_lock loops
Convert those common loops using page_table_lock on the outside and
pte_offset_map within to use just pte_offset_map_lock within instead.

These all hold mmap_sem (some exclusively, some not), so at no level can
a page table be whipped away from beneath them. But whereas pte_alloc
loops tested with the "atomic" pmd_present, these loops are testing with
pmd_none, which on i386 PAE tests both lower and upper halves.

That's now unsafe, so add a cast into pmd_none to test only the vital
lower half: we lose a little sensitivity to a corrupt middle directory,
but not enough to worry about. It appears that i386 and UML were the
only architectures vulnerable in this way, and pgd and pud no problem.

Signed-off-by: Hugh Dickins <hugh@veritas.com>
---
fs/proc/task_mmu.c | 17 ++++++-----------
include/asm-i386/pgtable.h | 3 ++-
include/asm-um/pgtable.h | 2 +-
mm/mempolicy.c | 7 +++----
mm/mprotect.c | 7 +++----
mm/msync.c | 21 ++++++---------------
mm/swapfile.c | 20 +++++++++-----------
7 files changed, 30 insertions(+), 47 deletions(-)
--- mm13/fs/proc/task_mmu.c 2005-10-11 23:54:33.000000000 +0100
+++ mm14/fs/proc/task_mmu.c 2005-10-11 23:57:10.000000000 +0100
@@ -203,13 +203,14 @@ static void smaps_pte_range(struct vm_ar
struct mem_size_stats *mss)
{
pte_t *pte, ptent;
+ spinlock_t *ptl;
unsigned long pfn;
struct page *page;

- pte = pte_offset_map(pmd, addr);
+ pte = pte_offset_map_lock(vma->vm_mm, pmd, addr, &ptl);
do {
ptent = *pte;
- if (pte_none(ptent) || !pte_present(ptent))
+ if (!pte_present(ptent))
continue;

mss->resident += PAGE_SIZE;
@@ -230,8 +231,8 @@ static void smaps_pte_range(struct vm_ar
mss->private_clean += PAGE_SIZE;
}
} while (pte++, addr += PAGE_SIZE, addr != end);
- pte_unmap(pte - 1);
- cond_resched_lock(&vma->vm_mm->page_table_lock);
+ pte_unmap_unlock(pte - 1, ptl);
+ cond_resched();
}

static inline void smaps_pmd_range(struct vm_area_struct *vma, pud_t *pud,
@@ -285,17 +286,11 @@ static inline void smaps_pgd_range(struc
static int show_smap(struct seq_file *m, void *v)
{
struct vm_area_struct *vma = v;
- struct mm_struct *mm = vma->vm_mm;
struct mem_size_stats mss;

memset(&mss, 0, sizeof mss);
-
- if (mm) {
- spin_lock(&mm->page_table_lock);
+ if (vma->vm_mm)
smaps_pgd_range(vma, vma->vm_start, vma->vm_end, &mss);
- spin_unlock(&mm->page_table_lock);
- }
-
return show_map_internal(m, v, &mss);
}

--- mm13/include/asm-i386/pgtable.h 2005-09-30 11:59:09.000000000 +0100
+++ mm14/include/asm-i386/pgtable.h 2005-10-11 23:57:10.000000000 +0100
@@ -213,7 +213,8 @@ extern unsigned long pg0[];
#define pte_present(x) ((x).pte_low & (_PAGE_PRESENT | _PAGE_PROTNONE))
#define pte_clear(mm,addr,xp) do { set_pte_at(mm, addr, xp, __pte(0)); } while (0)

-#define pmd_none(x) (!pmd_val(x))
+/* To avoid harmful races, pmd_none(x) should check only the lower when PAE */
+#define pmd_none(x) (!(unsigned long)pmd_val(x))
#define pmd_present(x) (pmd_val(x) & _PAGE_PRESENT)
#define pmd_clear(xp) do { set_pmd(xp, __pmd(0)); } while (0)
#define pmd_bad(x) ((pmd_val(x) & (~PAGE_MASK & ~_PAGE_USER)) != _KERNPG_TABLE)
--- mm13/include/asm-um/pgtable.h 2005-0OB9-30 11:59:10.000000000 +0100
+++ mm14/include/asm-um/pgtable.h 2005-10-11 23:57:10.000000000 +0100
@@ -138,7 +138,7 @@ extern unsigned long pg0[1024];

#define pte_clear(mm,addr,xp) pte_set_val(*(xp), (phys_t) 0, __pgprot(_PAGE_NEWPAGE))

-#define pmd_none(x) (!(pmd_val(x) & ~_PAGE_NEWPAGE))
+#define pmd_none(x) (!((unsigned long)pmd_val(x) & ~_PAGE_NEWPAGE))
#define pmd_bad(x) ((pmd_val(x) & (~PAGE_MASK & ~_PAGE_USER)) != _KERNPG_TABLE)
#define pmd_present(x) (pmd_val(x) & _PAGE_PRESENT)
#define pmd_clear(xp) do { pmd_val(*(xp)) = _PAGE_NEWPAGE; } while (0)
--- mm13/mm/mempolicy.c 2005-10-11 12:16:50.000000000 +0100
+++ mm14/mm/mempolicy.c 2005-10-11 23:57:10.000000000 +0100
@@ -228,9 +228,9 @@ static int check_pte_range(struct vm_are
{
pte_t *orig_pte;
pte_t *pte;
+ spinlock_t *ptl;

- spin_lock(&vma->vm_mm->page_table_lock);
- orig_pte = pte = pte_offset_map(pmd, addr);
+ orig_pte = pte = pte_offset_map_lock(vma->vm_mm, pmd, addr, &ptl);
do {
unsigned long pfn;
unsigned int nid;
@@ -246,8 +246,7 @@ static int check_pte_range(struct vm_are
if (!node_isset(nid, *nodes))
break;
} while (pte++, addr += PAGE_SIZE, addr != end);
- pte_unmap(orig_pte);
- spin_unlock(&vma->vm_mm->page_table_lock);
+ pte_unmap_unlock(orig_pte, ptl);
return addr != end;
}

--- mm13/mm/mprotect.c 2005-10-11 12:16:50.000000000 +0100
+++ mm14/mm/mprotect.c 2005-10-11 23:57:10.000000000 +0100
@@ -29,8 +29,9 @@ static void change_pte_range(struct mm_s
unsigned long addr, unsigned long end, pgprot_t newprot)
{
pte_t *pte;
+ spinlock_t *ptl;

- pte = pte_offset_map(pmd, addr);
+ pte = pte_offset_map_lock(mm, pmd, addr, &ptl);
do {
if (pte_present(*pte)) {
pte_t ptent;
@@ -44,7 +45,7 @@ static void change_pte_range(struct mm_s
lazy_mmu_prot_update(ptent);
}
} while (pte++, addr += PAGE_SIZE, addr != end);
- pte_unmap(pte - 1);
+ pte_unmap_unlock(pte - 1, ptl);
}

static inline void change_pmd_range(struct mm_struct *mm, pud_t *pud,
@@ -88,7 +89,6 @@ static void change_protection(struct vm_
BUG_ON(addr >= end);
pgd = pgd_offset(mm, addr);
flush_cache_range(vma, addr, end);
- spin_lock(&mm->page_table_lock);
do {
next = pgd_addr_end(addr, end);
if (pgd_none_or_clear_bad(pgd))
@@ -96,7 +96,6 @@ static void change_protection(struct vm_
change_pud_range(mm, pgd, addr, next, newprot);
} while (pgd++, addr = next, addr != end);
flush_tlb_range(vma, start, end);
- spin_unlock(&mm->page_table_lock);
}

static int
--- mm13/mm/msync.c 2005-10-11 12:16:50.000000000 +0100
+++ mm14/mm/msync.c 2005-10-11 23:57:10.000000000 +0100
@@ -17,28 +17,22 @@
#include <asm/pgtable.h>
#include <asm/tlbflush.h>

-/*
- * Called with mm->page_table_lock held to protect against other
- * threads/the swapper from ripping pte's out from under us.
- */
-
static void msync_pte_range(struct vm_area_struct *vma, pmd_t *pmd,
unsigned long addr, unsigned long end)
{
- struct mm_struct *mm = vma->vm_mm;
pte_t *pte;
+ spinlock_t *ptl;
int progress = 0;

again:
- pte = pte_offset_map(pmd, addr);
+ pte = pte_offset_map_lock(vma->vm_mm, pmd, addr, &ptl);
do {
unsigned long pfn;
struct page *page;

if (progress >= 64) {
progress = 0;
- if (need_resched() ||
- need_lockbreak(&mm->page_table_lock))
+ if (need_resched() || need_lockbreak(ptl))
break;
}
progress++;
@@ -58,8 +52,8 @@ again:
set_page_dirty(page);
progress += 3;
} while (pte++, addr += PAGE_SIZE, addr != end);
- pte_unmap(pte - 1);
- cond_resched_lock(&mm->page_table_lock);
+ pte_unmap_unlock(pte - 1, ptl);
+ cond_resched();
if (addr != end)
goto again;
}
@@ -97,7 +91,6 @@ static inline void msync_pud_range(struc
static void msync_page_range(struct vm_area_struct *vma,
unsigned long addr, unsigned long end)
{
- struct mm_struct *mm = vma->vm_mm;
pgd_t *pgd;
unsigned long next;

@@ -110,16 +103,14 @@ static void msync_page_range(struct vm_a
return;

BUG_ON(addr >= end);
- pgd = pgd_offset(mm, addr);
+ pgd = pgd_offset(vma->vm_mm, addr);
flush_cache_range(vma, addr, end);
- spin_lock(&mm->page_table_lock);
do {
next = pgd_addr_end(addr, end);
if (pgd_none_or_clear_bad(pgd))
continue;
msync_pud_range(vma, pgd, addr, next);
} while (pgd++, addr = next, addr != end);
- spin_unlock(&mm->page_table_lock);
}

/*
--- mm13/mm/swapfile.c 2005-09-30 11:59:12.000000000 +0100
+++ mm14/mm/swapfile.c 2005-10-11 23:57:10.000000000 +0100
@@ -399,8 +399,6 @@ void free_swap_and_cache(swp_entry_t ent
* No need to decide whether this PTE shares the swap entry with others,
* just let do_wp_page work it out if a write is requested later - to
* force COW, vm_page_prot omits write permission from any private vma.
- *
- * vma->vm_mm->page_table_lock is held.
*/
static void unuse_pte(struct vm_area_struct *vma, pte_t *pte,
unsigned long addr, swp_entry_t entry, struct page *page)
@@ -422,23 +420,25 @@ static int unuse_pte_range(struct vm_are
unsigned long addr, unsigned long end,
swp_entry_t entry, struct page *page)
{
- pte_t *pte;
pte_t swp_pte = swp_entry_to_pte(entry);
+ pte_t *pte;
+ spinlock_t *ptl;
+ int found = 0;

- pte = pte_offset_map(pmd, addr);
+ pte = pte_offset_map_lock(vma->vm_mm, pmd, addr, &ptl);
do {
/*
* swapoff spends a _lot_ of time in this loop!
* Test inline before going to call unuse_pte.
*/
if (unlikely(pte_same(*pte, swp_pte))) {
- unuse_pte(vma, pte, addr, entry, page);
- pte_unmap(pte);
- return 1;
+ unuse_pte(vma, pte++, addr, entry, page);
+ found = 1;
+ break;
}
} while (pte++, addr += PAGE_SIZE, addr != end);
- pte_unmap(pte - 1);
- return 0;
+ pte_unmap_unlock(pte - 1, ptl);
+ return found;
}

static inline int unuse_pmd_range(struct vm_area_struct *vma, pud_t *pud,
@@ -520,12 +520,10 @@ static int unuse_mm(struct mm_struct *mm
down_read(&mm->mmap_sem);
lock_page(page);
}
- spin_lock(&mm->page_table_lock);
for (vma = mm->mmap; vma; vma = vma->vm_next) {
if (vma->anon_vma && unuse_vma(vma, entry, page))
break;
}
- spin_unlock(&mm->page_table_lock);
up_read(&mm->mmap_sem);
/*
* Currently unuse_mm cannot fail, but leave error handling
-
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