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Commit a9ff785e authored by Cliff Wickman's avatar Cliff Wickman Committed by Linus Torvalds
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mm/pagewalk.c: walk_page_range should avoid VM_PFNMAP areas 



A panic can be caused by simply cat'ing /proc/<pid>/smaps while an
application has a VM_PFNMAP range.  It happened in-house when a
benchmarker was trying to decipher the memory layout of his program.

/proc/<pid>/smaps and similar walks through a user page table should not
be looking at VM_PFNMAP areas.

Certain tests in walk_page_range() (specifically split_huge_page_pmd())
assume that all the mapped PFN's are backed with page structures.  And
this is not usually true for VM_PFNMAP areas.  This can result in panics
on kernel page faults when attempting to address those page structures.

There are a half dozen callers of walk_page_range() that walk through a
task's entire page table (as N.  Horiguchi pointed out).  So rather than
change all of them, this patch changes just walk_page_range() to ignore
VM_PFNMAP areas.

The logic of hugetlb_vma() is moved back into walk_page_range(), as we
want to test any vma in the range.

VM_PFNMAP areas are used by:
- graphics memory manager   gpu/drm/drm_gem.c
- global reference unit     sgi-gru/grufile.c
- sgi special memory        char/mspec.c
- and probably several out-of-tree modules

[akpm@linux-foundation.org: remove now-unused hugetlb_vma() stub]
Signed-off-by: default avatarCliff Wickman <cpw@sgi.com>
Reviewed-by: default avatarNaoya Horiguchi <n-horiguchi@ah.jp.nec.com>
Cc: Mel Gorman <mel@csn.ul.ie>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: Dave Hansen <dave.hansen@intel.com>
Cc: David Sterba <dsterba@suse.cz>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: KOSAKI Motohiro <kosaki.motohiro@gmail.com>
Cc: "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>
Cc: <stable@vger.kernel.org>
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
parent 43c523bf

mm/pagewalk.c

+36 −34
Original line number Diff line number Diff line
@@ -127,28 +127,7 @@ static int walk_hugetlb_range(struct vm_area_struct *vma, 
	return 0;

}



static struct vm_area_struct* hugetlb_vma(unsigned long addr, struct mm_walk *walk)

{

	struct vm_area_struct *vma;



	/* We don't need vma lookup at all. */

	if (!walk->hugetlb_entry)

		return NULL;



	VM_BUG_ON(!rwsem_is_locked(&walk->mm->mmap_sem));

	vma = find_vma(walk->mm, addr);

	if (vma && vma->vm_start <= addr && is_vm_hugetlb_page(vma))

		return vma;



	return NULL;

}



#else /* CONFIG_HUGETLB_PAGE */

static struct vm_area_struct* hugetlb_vma(unsigned long addr, struct mm_walk *walk)

{

	return NULL;

}



static int walk_hugetlb_range(struct vm_area_struct *vma,

			      unsigned long addr, unsigned long end,

			      struct mm_walk *walk)
@@ -198,24 +177,46 @@ int walk_page_range(unsigned long addr, unsigned long end, 
	if (!walk->mm)

		return -EINVAL;



	VM_BUG_ON(!rwsem_is_locked(&walk->mm->mmap_sem));



	pgd = pgd_offset(walk->mm, addr);

	do {

		struct vm_area_struct *vma;

		struct vm_area_struct *vma = NULL;



		next = pgd_addr_end(addr, end);



		/*

		 * 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.

		 * 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 = hugetlb_vma(addr, walk);

		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)) {

				next = vma->vm_end;

				pgd = pgd_offset(walk->mm, next);

				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.

				 * 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)
@@ -223,6 +224,7 @@ int walk_page_range(unsigned long addr, unsigned long end, 
				pgd = pgd_offset(walk->mm, next);

				continue;

			}

		}



		if (pgd_none_or_clear_bad(pgd)) {

			if (walk->pte_hole)