From 3999f52e3198e76607446ab1a4610c1ddc406c56 Mon Sep 17 00:00:00 2001 From: "Aneesh Kumar K.V" Date: Mon, 12 Dec 2016 16:41:56 -0800 Subject: [PATCH] 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 Reported-by: Jan Stancek Acked-by: Hillf Danton Cc: Mike Kravetz Cc: Scott Wood Cc: Michael Ellerman Cc: Kirill A. Shutemov Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds --- mm/hugetlb.c | 12 +++++++----- 1 file 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); -- 2.20.1