linux-kernel - Re: [PATCH 1/2] mm: Mark nr_node_ids __ro_after

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Message-ID: <20230802145809.GE2607694@kernel.org>
Date:   Wed, 2 Aug 2023 17:58:09 +0300
From:   Mike Rapoport <rppt@...nel.org>
To:     Peter Zijlstra <peterz@...radead.org>
Cc:     yury.norov@...il.com, andriy.shevchenko@...ux.intel.com,
        linux@...musvillemoes.dk,
        Andrew Morton <akpm@...ux-foundation.org>,
        linux-kernel@...r.kernel.org, linux-mm@...ck.org,
        tglx@...utronix.de
Subject: Re: [PATCH 1/2] mm: Mark nr_node_ids __ro_after_init

On Wed, Aug 02, 2023 at 01:24:59PM +0200, Peter Zijlstra wrote:
> Just like nr_cpu_ids, nr_node_ids covers the side of possible_map and
> is thus constant after init.
> 
> Mark the variable __ro_after_init to both improve performance and
> enhance security, since the variable is exported. A module writing to
> it would be 'unfortunate'.
> 
> Signed-off-by: Peter Zijlstra (Intel) <peterz@...radead.org>

Reviewed-by: Mike Rapoport (IBM) <rppt@...nel.org>

> ---
>  mm/page_alloc.c |    2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> --- a/mm/page_alloc.c
> +++ b/mm/page_alloc.c
> @@ -305,7 +305,7 @@ int movable_zone;
>  EXPORT_SYMBOL(movable_zone);
>  
>  #if MAX_NUMNODES > 1
> -unsigned int nr_node_ids __read_mostly = MAX_NUMNODES;
> +unsigned int nr_node_ids __ro_after_init = MAX_NUMNODES;
>  unsigned int nr_online_nodes __read_mostly = 1;
>  EXPORT_SYMBOL(nr_node_ids);
>  EXPORT_SYMBOL(nr_online_nodes);
> 
> 

-- 
Sincerely yours,
Mike.