linux-kernel - Re: [PATCH v1] mm: use ptep_get() instead of directly dereferencing pte

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Message-ID: <3157f1d4-7248-4268-90fd-62ef1d3cb868@lucifer.local>
Date: Mon, 10 Mar 2025 14:10:15 +0000
From: Lorenzo Stoakes <lorenzo.stoakes@...cle.com>
To: Ryan Roberts <ryan.roberts@....com>
Cc: Andrew Morton <akpm@...ux-foundation.org>, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v1] mm: use ptep_get() instead of directly dereferencing
 pte_t*

On Mon, Mar 10, 2025 at 02:04:17PM +0000, Ryan Roberts wrote:
> It is best practice for all pte accesses to go via the arch helpers, to
> ensure non-torn values and to allow the arch to intervene where needed
> (contpte for arm64 for example). While in this case it was probably safe
> to directly dereference, let's tidy it up for consistency.
>
> Signed-off-by: Ryan Roberts <ryan.roberts@....com>

LGTM, so:

Reviewed-by: Lorenzo Stoakes <lorenzo.stoakes@...cle.com>

> ---
>  mm/migrate.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/mm/migrate.c b/mm/migrate.c
> index 22e270f727ed..33a22c2d6b20 100644
> --- a/mm/migrate.c
> +++ b/mm/migrate.c
> @@ -202,7 +202,7 @@ static bool try_to_map_unused_to_zeropage(struct page_vma_mapped_walk *pvmw,
>  		return false;
>  	VM_BUG_ON_PAGE(!PageAnon(page), page);
>  	VM_BUG_ON_PAGE(!PageLocked(page), page);
> -	VM_BUG_ON_PAGE(pte_present(*pvmw->pte), page);
> +	VM_BUG_ON_PAGE(pte_present(ptep_get(pvmw->pte)), page);
>
>  	if (folio_test_mlocked(folio) || (pvmw->vma->vm_flags & VM_LOCKED) ||
>  	    mm_forbids_zeropage(pvmw->vma->vm_mm))
> --
> 2.43.0
>