linux-kernel - Re: [PATCH] mm/ptdump: Replace READ_ONCE() with standard page table accessors

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Message-ID: <9736fd6a-8987-4b10-9b05-e03106463c34@arm.com>
Date: Tue, 30 Sep 2025 10:07:27 +0530
From: Dev Jain <dev.jain@....com>
To: Anshuman Khandual <anshuman.khandual@....com>, linux-mm@...ck.org
Cc: Andrew Morton <akpm@...ux-foundation.org>,
 David Hildenbrand <david@...hat.com>, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] mm/ptdump: Replace READ_ONCE() with standard page table
 accessors


On 30/09/25 8:22 am, Anshuman Khandual wrote:
> Replace READ_ONCE() with standard page table accessors i.e pxdp_get() which
> anyways default into READ_ONCE() in cases where platform does not override.
>
> Cc: Andrew Morton <akpm@...ux-foundation.org>
> Cc: David Hildenbrand <david@...hat.com>
> Cc: linux-mm@...ck.org
> Cc: linux-kernel@...r.kernel.org
> Signed-off-by: Anshuman Khandual <anshuman.khandual@....com>
> ---
>   mm/ptdump.c | 8 ++++----
>   1 file changed, 4 insertions(+), 4 deletions(-)
>
> diff --git a/mm/ptdump.c b/mm/ptdump.c
> index b600c7f864b8..18861501b533 100644
> --- a/mm/ptdump.c
> +++ b/mm/ptdump.c
> @@ -31,7 +31,7 @@ static int ptdump_pgd_entry(pgd_t *pgd, unsigned long addr,
>   			    unsigned long next, struct mm_walk *walk)
>   {
>   	struct ptdump_state *st = walk->private;
> -	pgd_t val = READ_ONCE(*pgd);
> +	pgd_t val = pgdp_get(pgd);
>   
>   #if CONFIG_PGTABLE_LEVELS > 4 && \
>   		(defined(CONFIG_KASAN_GENERIC) || defined(CONFIG_KASAN_SW_TAGS))
> @@ -54,7 +54,7 @@ static int ptdump_p4d_entry(p4d_t *p4d, unsigned long addr,
>   			    unsigned long next, struct mm_walk *walk)
>   {
>   	struct ptdump_state *st = walk->private;
> -	p4d_t val = READ_ONCE(*p4d);
> +	p4d_t val = p4dp_get(p4d);
>   
>   #if CONFIG_PGTABLE_LEVELS > 3 && \
>   		(defined(CONFIG_KASAN_GENERIC) || defined(CONFIG_KASAN_SW_TAGS))
> @@ -77,7 +77,7 @@ static int ptdump_pud_entry(pud_t *pud, unsigned long addr,
>   			    unsigned long next, struct mm_walk *walk)
>   {
>   	struct ptdump_state *st = walk->private;
> -	pud_t val = READ_ONCE(*pud);
> +	pud_t val = pudp_get(pud);
>   
>   #if CONFIG_PGTABLE_LEVELS > 2 && \
>   		(defined(CONFIG_KASAN_GENERIC) || defined(CONFIG_KASAN_SW_TAGS))
> @@ -100,7 +100,7 @@ static int ptdump_pmd_entry(pmd_t *pmd, unsigned long addr,
>   			    unsigned long next, struct mm_walk *walk)
>   {
>   	struct ptdump_state *st = walk->private;
> -	pmd_t val = READ_ONCE(*pmd);
> +	pmd_t val = pmdp_get(pmd);

I believe this should go through pmdp_get_lockless(). I can see in pgtable.h that
some magic is required on some arches to decode the pmd correctly in case walking
without locks.

Reviewed-by: Dev Jain <dev.jain@....com>