Re: [PATCH] fork: zero vmap stack using clear_pages() instead of memset()

["David Hildenbrand (Arm)" <david@kernel.org>]

On 2/24/26 11:26, Linus Walleij wrote:
> After the introduction of clear_pages() we exploit the
> fact that the process vm_area is allocated in contiguous
> pages to just clear them all in one swift operation.

The pages are virtually contiguous (vmalloc IIUC), not necessarily
physically contiguous. For clear_pages() that should work.

> 
> Suggested-by: Mateusz Guzik <mjguzik@gmail.com>
> Link: https://lore.kernel.org/linux-mm/dpnwsp7dl4535rd7qmszanw6u5an2p74uxfex4dh53frpb7pu3@2bnjjavjrepe/
> Suggested-by: Pasha Tatashin <pasha.tatashin@soleen.com>
> Link: https://lore.kernel.org/20240311164638.2015063-7-pasha.tatashin@soleen.com
> Signed-off-by: Linus Walleij <linusw@kernel.org>
> ---
>  kernel/fork.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/kernel/fork.c b/kernel/fork.c
> index e832da9d15a4..88d78ccef245 100644
> --- a/kernel/fork.c
> +++ b/kernel/fork.c
> @@ -345,7 +345,7 @@ static int alloc_thread_stack_node(struct task_struct *tsk, int node)
>  		stack = kasan_reset_tag(vm_area->addr);
>  
>  		/* Clear stale pointers from reused stack. */
> -		memset(stack, 0, THREAD_SIZE);
> +		clear_pages(vm_area->addr, vm_area->nr_pages);

LGTM.

Do we have any idea about performance impact etc?

-- 
Cheers,

David