From: Janosch Frank frankja@linux.ibm.com Subject: userfaultfd: hugetlbfs: fix userfaultfd_huge_must_wait() pte access

Use huge_ptep_get() to translate huge ptes to normal ptes so we can check them with the huge_pte_* functions. Otherwise some architectures will check the wrong values and will not wait for userspace to bring in the memory.

Link: http://lkml.kernel.org/r/20180626132421.78084-1-frankja@linux.ibm.com Fixes: 369cd2121be4 ("userfaultfd: hugetlbfs: userfaultfd_huge_must_wait for hugepmd ranges") Signed-off-by: Janosch Frank frankja@linux.ibm.com Reviewed-by: David Hildenbrand david@redhat.com Reviewed-by: Mike Kravetz mike.kravetz@oracle.com Cc: Andrea Arcangeli aarcange@redhat.com Cc: stable@vger.kernel.org Signed-off-by: Andrew Morton akpm@linux-foundation.org ---

fs/userfaultfd.c | 12 +++++++----- 1 file changed, 7 insertions(+), 5 deletions(-)

diff -puN fs/userfaultfd.c~userfaultfd-hugetlbfs-fix-userfaultfd_huge_must_wait-pte-access fs/userfaultfd.c --- a/fs/userfaultfd.c~userfaultfd-hugetlbfs-fix-userfaultfd_huge_must_wait-pte-access +++ a/fs/userfaultfd.c @@ -222,24 +222,26 @@ static inline bool userfaultfd_huge_must unsigned long reason) { struct mm_struct *mm = ctx->mm; - pte_t *pte; + pte_t *ptep, pte; bool ret = true;

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

- pte = huge_pte_offset(mm, address, vma_mmu_pagesize(vma)); - if (!pte) + ptep = huge_pte_offset(mm, address, vma_mmu_pagesize(vma)); + + if (!ptep) goto out;

ret = false; + pte = huge_ptep_get(ptep);

/* * Lockless access: we're in a wait_event so it's ok if it * changes under us. */ - if (huge_pte_none(*pte)) + if (huge_pte_none(pte)) ret = true; - if (!huge_pte_write(*pte) && (reason & VM_UFFD_WP)) + if (!huge_pte_write(pte) && (reason & VM_UFFD_WP)) ret = true; out: return ret; _