On Thu, Aug 15, 2019 at 08:52:56PM +0000, Yang, Philip wrote:
> hmm_range_fault may return NULL pages because some of pfns are equal to
> HMM_PFN_NONE. This happens randomly under memory pressure. The reason is
> for swapped out page pte path, hmm_vma_handle_pte doesn't update fault
> variable from cpu_flags, so it failed to call hmm_vam_do_fault to swap
> the page in.
>
> The fix is to call hmm_pte_need_fault to update fault variable.
>
> Change-Id: I2e8611485563d11d938881c18b7935fa1e7c91ee
> Signed-off-by: Philip Yang <Philip.Yang@xxxxxxx>
Reviewed-by: Jérôme Glisse <jglisse@xxxxxxxxxx>
> ---
> mm/hmm.c | 3 +++
> 1 file changed, 3 insertions(+)
>
> diff --git a/mm/hmm.c b/mm/hmm.c
> index 9f22562e2c43..7ca4fb39d3d8 100644
> --- a/mm/hmm.c
> +++ b/mm/hmm.c
> @@ -544,6 +544,9 @@ static int hmm_vma_handle_pte(struct mm_walk *walk, unsigned long addr,
> swp_entry_t entry = pte_to_swp_entry(pte);
>
> if (!non_swap_entry(entry)) {
> + cpu_flags = pte_to_hmm_pfn_flags(range, pte);
> + hmm_pte_need_fault(hmm_vma_walk, orig_pfn, cpu_flags,
> + &fault, &write_fault);
> if (fault || write_fault)
> goto fault;
> return 0;
> --
> 2.17.1
>
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