Skip to content

Commit

Permalink
pagewalk: improve vma handling
Browse files Browse the repository at this point in the history 
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>
  • Loading branch information
Naoya Horiguchi authored and Linus Torvalds committed Feb 12, 2015
1 parent 0b1fbfe commit fafaa42
Show file tree
Hide file tree
Showing 2 changed files with 129 additions and 92 deletions.
15 changes: 12 additions & 3 deletions include/linux/mm.h
View file
Original file line number Diff line number Diff line change
Expand Up @@ -1171,10 +1171,16 @@ void unmap_vmas(struct mmu_gather *tlb, struct vm_area_struct *start_vma,
* @pte_entry: if set, called for each non-empty PTE (4th-level) entry
* @pte_hole: if set, called for each hole at all levels
* @hugetlb_entry: if set, called for each hugetlb entry
* *Caution*: The caller must hold mmap_sem() if @hugetlb_entry
* is used.
* @test_walk: caller specific callback function to determine whether
* we walk over the current vma or not. A positive returned
* value means "do page table walk over the current vma,"
* and a negative one means "abort current page table walk
* right now." 0 means "skip the current vma."
* @mm: mm_struct representing the target process of page table walk
* @vma: vma currently walked (NULL if walking outside vmas)
* @private: private data for callbacks' usage
*
* (see walk_page_range for more details)
* (see the comment on walk_page_range() for more details)
*/
struct mm_walk {
int (*pmd_entry)(pmd_t *pmd, unsigned long addr,
Expand All @@ -1186,7 +1192,10 @@ struct mm_walk {
int (*hugetlb_entry)(pte_t *pte, unsigned long hmask,
unsigned long addr, unsigned long next,
struct mm_walk *walk);
int (*test_walk)(unsigned long addr, unsigned long next,
struct mm_walk *walk);
struct mm_struct *mm;
struct vm_area_struct *vma;
void *private;
};

Expand Down
206 changes: 117 additions & 89 deletions mm/pagewalk.c
View file
Original file line number Diff line number Diff line change
Expand Up @@ -59,7 +59,7 @@ static int walk_pmd_range(pud_t *pud, unsigned long addr, unsigned long end,
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)
Expand Down Expand Up @@ -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)
Expand All @@ -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);
Expand All @@ -119,128 +145,130 @@ 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;
}

#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;
}

0 comments on commit fafaa42

Please sign in to comment.