Re: [PATCH 4/6] x86/kasan: Prepare clear_pgds() to switch to <asm-generic/pgtable-nop4d.h>

[Andrey Ryabinin]

On 03/17/2017 09:55 PM, Kirill A. Shutemov wrote:
> With folded p4d, pgd_clear() is nop. Change clear_pgds() to use
> p4d_clear() instead.
> 

You could probably just use set_pgd(pgd_offset_k(start), __pgd(0)); instead of pgd_clear()
as we already do in arm64.
It's basically pgd_clear() except it's not a nop wih p4d folded.


> Signed-off-by: Kirill A. Shutemov <kirill.shutemov@xxxxxxxxxxxxxxx>
> Cc: Dmitry Vyukov <dvyukov@xxxxxxxxxx>
> ---
>  arch/x86/mm/kasan_init_64.c | 15 +++++++++++++--
>  1 file changed, 13 insertions(+), 2 deletions(-)
> 
> diff --git a/arch/x86/mm/kasan_init_64.c b/arch/x86/mm/kasan_init_64.c
> index 0a56059a95c7..b775ffd7989d 100644
> --- a/arch/x86/mm/kasan_init_64.c
> +++ b/arch/x86/mm/kasan_init_64.c
> @@ -35,8 +35,19 @@ static int __init map_range(struct range *range)
>  static void __init clear_pgds(unsigned long start,
>  			unsigned long end)
>  {
> -	for (; start < end; start += PGDIR_SIZE)
> -		pgd_clear(pgd_offset_k(start));
> +	pgd_t *pgd;
> +
> +	for (; start < end; start += PGDIR_SIZE) {
> +		pgd = pgd_offset_k(start);
> +		/*
> +		 * With folded p4d, pgd_clear() is nop, use p4d_clear()
> +		 * instead.
> +		 */
> +		if (CONFIG_PGTABLE_LEVELS < 5)
> +			p4d_clear(p4d_offset(pgd, start));
> +		else
> +			pgd_clear(pgd);
> +	}
>  }
>  
>  static void __init kasan_map_early_shadow(pgd_t *pgd)
>