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authorAneesh Kumar K.V <aneesh.kumar@linux.vnet.ibm.com>2016-12-13 03:41:56 +0300
committerLinus Torvalds <torvalds@linux-foundation.org>2016-12-13 05:55:07 +0300
commit3999f52e3198e76607446ab1a4610c1ddc406c56 (patch)
tree78469e2ed7888389cabfe8270e51fdcd3b308d2a /mm/hugetlb.c
parent771ab4302c592d1de9e6b73f58979e9e5c424f4c (diff)
downloadlinux-3999f52e3198e76607446ab1a4610c1ddc406c56.tar.xz
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@linux.vnet.ibm.com Signed-off-by: Aneesh Kumar K.V <aneesh.kumar@linux.vnet.ibm.com> Reported-by: Jan Stancek <jstancek@redhat.com> Acked-by: Hillf Danton <hillf.zj@alibaba-inc.com> Cc: Mike Kravetz <mike.kravetz@oracle.com> Cc: Scott Wood <scottwood@freescale.com> Cc: Michael Ellerman <mpe@ellerman.id.au> Cc: Kirill A. Shutemov <kirill.shutemov@linux.intel.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Diffstat (limited to 'mm/hugetlb.c')
-rw-r--r--mm/hugetlb.c12
1 files changed, 7 insertions, 5 deletions
diff --git a/mm/hugetlb.c b/mm/hugetlb.c
index 418bf01a50ed..23aec01836aa 100644
--- a/mm/hugetlb.c
+++ b/mm/hugetlb.c
@@ -3450,15 +3450,17 @@ static void unmap_ref_private(struct mm_struct *mm, struct vm_area_struct *vma,
* 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:
@@ -3733,7 +3735,7 @@ 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);
@@ -3888,8 +3890,8 @@ int hugetlb_fault(struct mm_struct *mm, struct vm_area_struct *vma,
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);