Re: [PATCH] mm/hmm: hmm_range_fault handle pages swapped out

[Jerome Glisse <jglisse@redhat.com>]

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@amd.com>

Reviewed-by: Jérôme Glisse <jglisse@redhat.com>

> ---
>  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
>