linux-kernel - Re: [PATCH] mm: userfaultfd: fix unexpected change to src_folio when UFFDIO

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Date: Thu, 22 Feb 2024 09:43:27 +0100
From: David Hildenbrand <david@...hat.com>
To: Qi Zheng <zhengqi.arch@...edance.com>, akpm@...ux-foundation.org,
 aarcange@...hat.com, surenb@...gle.com
Cc: linux-mm@...ck.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] mm: userfaultfd: fix unexpected change to src_folio when
 UFFDIO_MOVE fails

On 22.02.24 09:08, Qi Zheng wrote:
> After ptep_clear_flush(), if we find that src_folio is pinned we will fail
> UFFDIO_MOVE and put src_folio back to src_pte entry, but the change to
> src_folio->{mapping,index} is not restored in this process. This is not
> what we expected, so fix it.
> 
> Fixes: adef440691ba ("userfaultfd: UFFDIO_MOVE uABI")
> Signed-off-by: Qi Zheng <zhengqi.arch@...edance.com>
> ---
>   mm/userfaultfd.c | 6 +++---
>   1 file changed, 3 insertions(+), 3 deletions(-)
> 
> diff --git a/mm/userfaultfd.c b/mm/userfaultfd.c
> index 4744d6a96f96..503ea77c81aa 100644
> --- a/mm/userfaultfd.c
> +++ b/mm/userfaultfd.c
> @@ -1008,9 +1008,6 @@ static int move_present_pte(struct mm_struct *mm,
>   		goto out;
>   	}
>   
> -	folio_move_anon_rmap(src_folio, dst_vma);
> -	WRITE_ONCE(src_folio->index, linear_page_index(dst_vma, dst_addr));
> -
>   	orig_src_pte = ptep_clear_flush(src_vma, src_addr, src_pte);
>   	/* Folio got pinned from under us. Put it back and fail the move. */
>   	if (folio_maybe_dma_pinned(src_folio)) {
> @@ -1019,6 +1016,9 @@ static int move_present_pte(struct mm_struct *mm,
>   		goto out;
>   	}
>   
> +	folio_move_anon_rmap(src_folio, dst_vma);
> +	WRITE_ONCE(src_folio->index, linear_page_index(dst_vma, dst_addr));
> +
>   	orig_dst_pte = mk_pte(&src_folio->page, dst_vma->vm_page_prot);
>   	/* Follow mremap() behavior and treat the entry dirty after the move */
>   	orig_dst_pte = pte_mkwrite(pte_mkdirty(orig_dst_pte), dst_vma);

Indeed, LGTM.

Reviewed-by: David Hildenbrand <david@...hat.com>

-- 
Cheers,

David / dhildenb