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authorNaoya Horiguchi <n-horiguchi@ah.jp.nec.com>2015-02-11 15:27:37 -0800
committerLinus Torvalds <torvalds@linux-foundation.org>2015-02-11 17:06:05 -0800
commitfafaa4264eba49fd10695c193a82760558d093f4 (patch)
tree2ba4ceadd17b4b93b3ba52e410af9e3c93312c4c /mm/pagewalk.c
parent0b1fbfe50006c41014cc25660c0e735d21c34939 (diff)
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pagewalk: improve vma handling
Current implementation of page table walker has a fundamental problem in vma handling, which started when we tried to handle vma(VM_HUGETLB). Because it's done in pgd loop, considering vma boundary makes code complicated and bug-prone. From the users viewpoint, some user checks some vma-related condition to determine whether the user really does page walk over the vma. In order to solve these, this patch moves vma check outside pgd loop and introduce a new callback ->test_walk(). Signed-off-by: Naoya Horiguchi <n-horiguchi@ah.jp.nec.com> Acked-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com> Cc: "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com> Cc: Andrea Arcangeli <aarcange@redhat.com> Cc: Cyrill Gorcunov <gorcunov@openvz.org> Cc: Dave Hansen <dave.hansen@intel.com> Cc: Pavel Emelyanov <xemul@parallels.com> Cc: Benjamin Herrenschmidt <benh@kernel.crashing.org> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Diffstat (limited to 'mm/pagewalk.c')
-rw-r--r--mm/pagewalk.c206
1 files changed, 117 insertions, 89 deletions
diff --git a/mm/pagewalk.c b/mm/pagewalk.c
index b793ef149da2..d9cc3caae802 100644
--- a/mm/pagewalk.c
+++ b/mm/pagewalk.c
@@ -59,7 +59,7 @@ again:
continue;
split_huge_page_pmd_mm(walk->mm, addr, pmd);
- if (pmd_none_or_trans_huge_or_clear_bad(pmd))
+ if (pmd_trans_unstable(pmd))
goto again;
err = walk_pte_range(pmd, addr, next, walk);
if (err)
@@ -95,6 +95,32 @@ static int walk_pud_range(pgd_t *pgd, unsigned long addr, unsigned long end,
return err;
}
+static int walk_pgd_range(unsigned long addr, unsigned long end,
+ struct mm_walk *walk)
+{
+ pgd_t *pgd;
+ unsigned long next;
+ int err = 0;
+
+ pgd = pgd_offset(walk->mm, addr);
+ do {
+ next = pgd_addr_end(addr, end);
+ if (pgd_none_or_clear_bad(pgd)) {
+ if (walk->pte_hole)
+ err = walk->pte_hole(addr, next, walk);
+ if (err)
+ break;
+ continue;
+ }
+ if (walk->pmd_entry || walk->pte_entry)
+ err = walk_pud_range(pgd, addr, next, walk);
+ if (err)
+ break;
+ } while (pgd++, addr = next, addr != end);
+
+ return err;
+}
+
#ifdef CONFIG_HUGETLB_PAGE
static unsigned long hugetlb_entry_end(struct hstate *h, unsigned long addr,
unsigned long end)
@@ -103,10 +129,10 @@ static unsigned long hugetlb_entry_end(struct hstate *h, unsigned long addr,
return boundary < end ? boundary : end;
}
-static int walk_hugetlb_range(struct vm_area_struct *vma,
- unsigned long addr, unsigned long end,
+static int walk_hugetlb_range(unsigned long addr, unsigned long end,
struct mm_walk *walk)
{
+ struct vm_area_struct *vma = walk->vma;
struct hstate *h = hstate_vma(vma);
unsigned long next;
unsigned long hmask = huge_page_mask(h);
@@ -119,15 +145,14 @@ static int walk_hugetlb_range(struct vm_area_struct *vma,
if (pte && walk->hugetlb_entry)
err = walk->hugetlb_entry(pte, hmask, addr, next, walk);
if (err)
- return err;
+ break;
} while (addr = next, addr != end);
- return 0;
+ return err;
}
#else /* CONFIG_HUGETLB_PAGE */
-static int walk_hugetlb_range(struct vm_area_struct *vma,
- unsigned long addr, unsigned long end,
+static int walk_hugetlb_range(unsigned long addr, unsigned long end,
struct mm_walk *walk)
{
return 0;
@@ -135,112 +160,115 @@ static int walk_hugetlb_range(struct vm_area_struct *vma,
#endif /* CONFIG_HUGETLB_PAGE */
+/*
+ * Decide whether we really walk over the current vma on [@start, @end)
+ * or skip it via the returned value. Return 0 if we do walk over the
+ * current vma, and return 1 if we skip the vma. Negative values means
+ * error, where we abort the current walk.
+ *
+ * Default check (only VM_PFNMAP check for now) is used when the caller
+ * doesn't define test_walk() callback.
+ */
+static int walk_page_test(unsigned long start, unsigned long end,
+ struct mm_walk *walk)
+{
+ struct vm_area_struct *vma = walk->vma;
+ if (walk->test_walk)
+ return walk->test_walk(start, end, walk);
+
+ /*
+ * Do not walk over vma(VM_PFNMAP), because we have no valid struct
+ * page backing a VM_PFNMAP range. See also commit a9ff785e4437.
+ */
+ if (vma->vm_flags & VM_PFNMAP)
+ return 1;
+ return 0;
+}
+
+static int __walk_page_range(unsigned long start, unsigned long end,
+ struct mm_walk *walk)
+{
+ int err = 0;
+ struct vm_area_struct *vma = walk->vma;
+
+ if (vma && is_vm_hugetlb_page(vma)) {
+ if (walk->hugetlb_entry)
+ err = walk_hugetlb_range(start, end, walk);
+ } else
+ err = walk_pgd_range(start, end, walk);
+
+ return err;
+}
/**
- * walk_page_range - walk a memory map's page tables with a callback
- * @addr: starting address
- * @end: ending address
- * @walk: set of callbacks to invoke for each level of the tree
- *
- * Recursively walk the page table for the memory area in a VMA,
- * calling supplied callbacks. Callbacks are called in-order (first
- * PGD, first PUD, first PMD, first PTE, second PTE... second PMD,
- * etc.). If lower-level callbacks are omitted, walking depth is reduced.
+ * walk_page_range - walk page table with caller specific callbacks
*
- * Each callback receives an entry pointer and the start and end of the
- * associated range, and a copy of the original mm_walk for access to
- * the ->private or ->mm fields.
+ * Recursively walk the page table tree of the process represented by @walk->mm
+ * within the virtual address range [@start, @end). During walking, we can do
+ * some caller-specific works for each entry, by setting up pmd_entry(),
+ * pte_entry(), and/or hugetlb_entry(). If you don't set up for some of these
+ * callbacks, the associated entries/pages are just ignored.
+ * The return values of these callbacks are commonly defined like below:
+ * - 0 : succeeded to handle the current entry, and if you don't reach the
+ * end address yet, continue to walk.
+ * - >0 : succeeded to handle the current entry, and return to the caller
+ * with caller specific value.
+ * - <0 : failed to handle the current entry, and return to the caller
+ * with error code.
*
- * Usually no locks are taken, but splitting transparent huge page may
- * take page table lock. And the bottom level iterator will map PTE
- * directories from highmem if necessary.
+ * Before starting to walk page table, some callers want to check whether
+ * they really want to walk over the current vma, typically by checking
+ * its vm_flags. walk_page_test() and @walk->test_walk() are used for this
+ * purpose.
*
- * If any callback returns a non-zero value, the walk is aborted and
- * the return value is propagated back to the caller. Otherwise 0 is returned.
+ * struct mm_walk keeps current values of some common data like vma and pmd,
+ * which are useful for the access from callbacks. If you want to pass some
+ * caller-specific data to callbacks, @walk->private should be helpful.
*
- * walk->mm->mmap_sem must be held for at least read if walk->hugetlb_entry
- * is !NULL.
+ * Locking:
+ * Callers of walk_page_range() and walk_page_vma() should hold
+ * @walk->mm->mmap_sem, because these function traverse vma list and/or
+ * access to vma's data.
*/
-int walk_page_range(unsigned long addr, unsigned long end,
+int walk_page_range(unsigned long start, unsigned long end,
struct mm_walk *walk)
{
- pgd_t *pgd;
- unsigned long next;
int err = 0;
+ unsigned long next;
+ struct vm_area_struct *vma;
- if (addr >= end)
- return err;
+ if (start >= end)
+ return -EINVAL;
if (!walk->mm)
return -EINVAL;
VM_BUG_ON_MM(!rwsem_is_locked(&walk->mm->mmap_sem), walk->mm);
- pgd = pgd_offset(walk->mm, addr);
+ vma = find_vma(walk->mm, start);
do {
- struct vm_area_struct *vma = NULL;
+ if (!vma) { /* after the last vma */
+ walk->vma = NULL;
+ next = end;
+ } else if (start < vma->vm_start) { /* outside vma */
+ walk->vma = NULL;
+ next = min(end, vma->vm_start);
+ } else { /* inside vma */
+ walk->vma = vma;
+ next = min(end, vma->vm_end);
+ vma = vma->vm_next;
- next = pgd_addr_end(addr, end);
-
- /*
- * This function was not intended to be vma based.
- * But there are vma special cases to be handled:
- * - hugetlb vma's
- * - VM_PFNMAP vma's
- */
- vma = find_vma(walk->mm, addr);
- if (vma) {
- /*
- * There are no page structures backing a VM_PFNMAP
- * range, so do not allow split_huge_page_pmd().
- */
- if ((vma->vm_start <= addr) &&
- (vma->vm_flags & VM_PFNMAP)) {
- if (walk->pte_hole)
- err = walk->pte_hole(addr, next, walk);
- if (err)
- break;
- pgd = pgd_offset(walk->mm, next);
+ err = walk_page_test(start, next, walk);
+ if (err > 0)
continue;
- }
- /*
- * Handle hugetlb vma individually because pagetable
- * walk for the hugetlb page is dependent on the
- * architecture and we can't handled it in the same
- * manner as non-huge pages.
- */
- if (walk->hugetlb_entry && (vma->vm_start <= addr) &&
- is_vm_hugetlb_page(vma)) {
- if (vma->vm_end < next)
- next = vma->vm_end;
- /*
- * Hugepage is very tightly coupled with vma,
- * so walk through hugetlb entries within a
- * given vma.
- */
- err = walk_hugetlb_range(vma, addr, next, walk);
- if (err)
- break;
- pgd = pgd_offset(walk->mm, next);
- continue;
- }
- }
-
- if (pgd_none_or_clear_bad(pgd)) {
- if (walk->pte_hole)
- err = walk->pte_hole(addr, next, walk);
- if (err)
+ if (err < 0)
break;
- pgd++;
- continue;
}
- if (walk->pmd_entry || walk->pte_entry)
- err = walk_pud_range(pgd, addr, next, walk);
+ if (walk->vma || walk->pte_hole)
+ err = __walk_page_range(start, next, walk);
if (err)
break;
- pgd++;
- } while (addr = next, addr < end);
-
+ } while (start = next, start < end);
return err;
}