Re: [PATCH v3 1/2] secretmem/gup: don't check if page is secretmem without reference

On 20.04.21 17:00, Mike Rapoport wrote:
> From: Mike Rapoport <[email protected]>
> 
> The check in gup_pte_range() whether a page belongs to a secretmem mapping
> is performed before grabbing the page reference.
> 
> To avoid potential race move the check after try_grab_compound_head().
> 
> Signed-off-by: Mike Rapoport <[email protected]>
> ---
>   mm/gup.c | 8 +++++---
>   1 file changed, 5 insertions(+), 3 deletions(-)
> 
> diff --git a/mm/gup.c b/mm/gup.c
> index c3a17b189064..6515f82b0f32 100644
> --- a/mm/gup.c
> +++ b/mm/gup.c
> @@ -2080,13 +2080,15 @@ static int gup_pte_range(pmd_t pmd, unsigned long addr, unsigned long end,
>   		VM_BUG_ON(!pfn_valid(pte_pfn(pte)));
>   		page = pte_page(pte);
>   
> -		if (page_is_secretmem(page))
> -			goto pte_unmap;
> -
>   		head = try_grab_compound_head(page, 1, flags);
>   		if (!head)
>   			goto pte_unmap;
>   
> +		if (unlikely(page_is_secretmem(page))) {
> +			put_compound_head(head, 1, flags);
> +			goto pte_unmap;
> +		}
> +
>   		if (unlikely(pte_val(pte) != pte_val(*ptep))) {
>   			put_compound_head(head, 1, flags);
>   			goto pte_unmap;
> 

Reviewed-by: David Hildenbrand <[email protected]>

-- 
Thanks,

David / dhildenb
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