[PATCH] userfaultfd: hugetlbfs: Fix userfaultfd_huge_must_wait pte access

[Janosch Frank]

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.

Signed-off-by: Janosch Frank <fran...@linux.ibm.com>
Fixes: 369cd2121be4 ("userfaultfd: hugetlbfs: userfaultfd_huge_must_wait for 
hugepmd ranges")
---
 fs/userfaultfd.c | 12 +++++++-----
 1 file changed, 7 insertions(+), 5 deletions(-)

diff --git a/fs/userfaultfd.c b/fs/userfaultfd.c
index 123bf7d516fc..594d192b2331 100644
--- a/fs/userfaultfd.c
+++ b/fs/userfaultfd.c
@@ -222,24 +222,26 @@ static inline bool userfaultfd_huge_must_wait(struct 
userfaultfd_ctx *ctx,
                                         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;
-- 
2.14.3