On 06/26/2018 06:24 AM, Janosch Frank wrote:
> 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 <frankja@xxxxxxxxxxxxx>
> Fixes: 369cd2121be4 ("userfaultfd: hugetlbfs: userfaultfd_huge_must_wait for hugepmd ranges")
Adding linux-mm and Andrew on Cc:
Thanks for catching and fixing this.
I think this needs to be fixed in stable as well. Correct? Assuming
userfaultfd is/can be enabled for impacted architectures.
Reviewed-by: Mike Kravetz <mike.kravetz@xxxxxxxxxx>
--
Mike Kravetz
> ---
> 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;
>
