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Message-Id: <E1Ucb6K-00047X-9I@eag09.americas.sgi.com>
Date: Wed, 15 May 2013 07:46:36 -0500
From: Cliff Wickman <cpw@....com>
To: linux-kernel@...r.kernel.org
Cc: akpm@...ux-foundation.org, mgorman@...e.de, aarcange@...hat.com,
dave.hansen@...el.com, dsterba@...e.cz, hannes@...xchg.org,
kosaki.motohiro@...il.com, kirill.shutemov@...ux.intel.com,
mpm@...enic.com, n-horiguchi@...jp.nec.com, rdunlap@...radead.org
Subject: [PATCH v3] mm/pagewalk.c: walk_page_range should avoid VM_PFNMAP areas
/proc/<pid>/smaps and similar walks through a user page table should not
be looking at VM_PFNMAP areas.
v2:
- moves the VM_BUG_ON out of the loop
- adds the needed test for vma->vm_start <= addr
v3 adds comments to make this clearer, as N. Horiguchi recommends:
> I recommend that you check VM_PFNMAP in the possible callers' side.
> But this patch seems to solve your problem, so with properly commenting
> this somewhere, I do not oppose it.
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
I'm copying everyone who has changed this file recently, in case
there is some reason that I am not aware of to provide
/proc/<pid>/smaps|clear_refs|maps|numa_maps for these VM_PFNMAP areas.
Signed-off-by: Cliff Wickman <cpw@....com>
---
mm/pagewalk.c | 65 ++++++++++++++++++++++++++++++++--------------------------
1 file changed, 36 insertions(+), 29 deletions(-)
Index: linux/mm/pagewalk.c
===================================================================
--- linux.orig/mm/pagewalk.c
+++ linux/mm/pagewalk.c
@@ -127,22 +127,6 @@ static int walk_hugetlb_range(struct vm_
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)
{
@@ -198,30 +182,53 @@ int walk_page_range(unsigned long addr,
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) {
- if (vma->vm_end < next)
+ /*
+ * 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;
+ }
/*
- * Hugepage is very tightly coupled with vma, so
- * walk through hugetlb entries within a given vma.
+ * 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.
*/
- err = walk_hugetlb_range(vma, addr, next, walk);
- if (err)
- break;
- pgd = pgd_offset(walk->mm, next);
- continue;
+ 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)) {
--
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