2023-08-02 13:38:04

by Peter Zijlstra

Subject: [PATCH 1/2] mm: Mark nr_node_ids __ro_after_init

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) <[email protected]>
---
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);

2023-08-02 15:13:53

by Mike Rapoport

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) <[email protected]>

Reviewed-by: Mike Rapoport (IBM) <[email protected]>

> ---
> 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.