The patch titled
Subject: mm/hugetlb.c: use the right pte val for compare in hugetlb_cow
has been added to the -mm tree. Its filename is
mm-hugetlb-use-the-right-pte-val-for-compare-in-hugetlb_cow.patch
This patch should soon appear at
http://ozlabs.org/~akpm/mmots/broken-out/mm-hugetlb-use-the-right-pte-val-for-compare-in-hugetlb_cow.patch
and later at
http://ozlabs.org/~akpm/mmotm/broken-out/mm-hugetlb-use-the-right-pte-val-for-compare-in-hugetlb_cow.patch
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From: "Aneesh Kumar K.V" <aneesh.kumar@xxxxxxxxxxxxxxxxxx>
Subject: mm/hugetlb.c: use the right pte val for compare in hugetlb_cow
We cannot use the pte value used in set_pte_at for pte_same comparison,
because archs like ppc64, filter/add new pte flag in set_pte_at. Instead
fetch the pte value inside hugetlb_cow. We are comparing pte value to
make sure the pte didn't change since we dropped the page table lock.
hugetlb_cow get called with page table lock held, and we can take a copy
of the pte value before we drop the page table lock.
With hugetlbfs, we optimize the MAP_PRIVATE write fault path with no
previous mapping (huge_pte_none entries), by forcing a cow in the fault
path. This avoid take an addition fault to covert a read-only mapping
to read/write. Here we were comparing a recently instantiated pte (via
set_pte_at) to the pte values from linux page table. As explained above
on ppc64 such pte_same check returned wrong result, resulting in us
taking an additional fault on ppc64.
Fixes: 6a119eae942c ("powerpc/mm: Add a _PAGE_PTE bit")
Link: http://lkml.kernel.org/r/20161018154245.18023-1-aneesh.kumar@xxxxxxxxxxxxxxxxxx
Signed-off-by: Aneesh Kumar K.V <aneesh.kumar@xxxxxxxxxxxxxxxxxx>
Reported-by: Jan Stancek <jstancek@xxxxxxxxxx>
Cc: Mike Kravetz <mike.kravetz@xxxxxxxxxx>
Cc: Scott Wood <scottwood@xxxxxxxxxxxxx>
Cc: Michael Ellerman <mpe@xxxxxxxxxxxxxx>
Cc: Kirill A. Shutemov <kirill.shutemov@xxxxxxxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
mm/hugetlb.c | 12 +++++++-----
1 file changed, 7 insertions(+), 5 deletions(-)
diff -puN mm/hugetlb.c~mm-hugetlb-use-the-right-pte-val-for-compare-in-hugetlb_cow mm/hugetlb.c
--- a/mm/hugetlb.c~mm-hugetlb-use-the-right-pte-val-for-compare-in-hugetlb_cow
+++ a/mm/hugetlb.c
@@ -3386,15 +3386,17 @@ static void unmap_ref_private(struct mm_
* Keep the pte_same checks anyway to make transition from the mutex easier.
*/
static int hugetlb_cow(struct mm_struct *mm, struct vm_area_struct *vma,
- unsigned long address, pte_t *ptep, pte_t pte,
- struct page *pagecache_page, spinlock_t *ptl)
+ unsigned long address, pte_t *ptep,
+ struct page *pagecache_page, spinlock_t *ptl)
{
+ pte_t pte;
struct hstate *h = hstate_vma(vma);
struct page *old_page, *new_page;
int ret = 0, outside_reserve = 0;
unsigned long mmun_start; /* For mmu_notifiers */
unsigned long mmun_end; /* For mmu_notifiers */
+ pte = huge_ptep_get(ptep);
old_page = pte_page(pte);
retry_avoidcopy:
@@ -3668,7 +3670,7 @@ retry:
hugetlb_count_add(pages_per_huge_page(h), mm);
if ((flags & FAULT_FLAG_WRITE) && !(vma->vm_flags & VM_SHARED)) {
/* Optimization, do the COW without a second fault */
- ret = hugetlb_cow(mm, vma, address, ptep, new_pte, page, ptl);
+ ret = hugetlb_cow(mm, vma, address, ptep, page, ptl);
}
spin_unlock(ptl);
@@ -3822,8 +3824,8 @@ int hugetlb_fault(struct mm_struct *mm,
if (flags & FAULT_FLAG_WRITE) {
if (!huge_pte_write(entry)) {
- ret = hugetlb_cow(mm, vma, address, ptep, entry,
- pagecache_page, ptl);
+ ret = hugetlb_cow(mm, vma, address, ptep,
+ pagecache_page, ptl);
goto out_put_page;
}
entry = huge_pte_mkdirty(entry);
_
Patches currently in -mm which might be from aneesh.kumar@xxxxxxxxxxxxxxxxxx are
mm-hugetlb-use-the-right-pte-val-for-compare-in-hugetlb_cow.patch
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