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

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Message-ID: <218853b4-3498-dab9-d1e9-02caed4d9322@virtuozzo.com>
Date:   Mon, 20 Mar 2017 19:21:20 +0300
From:   Andrey Ryabinin <aryabinin@...tuozzo.com>
To:     "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Andrew Morton <akpm@...ux-foundation.org>, <x86@...nel.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Arnd Bergmann <arnd@...db.de>,
        "H. Peter Anvin" <hpa@...or.com>
CC:     Andi Kleen <ak@...ux.intel.com>,
        Dave Hansen <dave.hansen@...el.com>,
        Andy Lutomirski <luto@...capital.net>,
        Michal Hocko <mhocko@...e.com>, <linux-arch@...r.kernel.org>,
        <linux-mm@...ck.org>, <linux-kernel@...r.kernel.org>,
        Dmitry Vyukov <dvyukov@...gle.com>
Subject: Re: [PATCH 4/6] x86/kasan: Prepare clear_pgds() to switch to
 <asm-generic/pgtable-nop4d.h>



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@...ux.intel.com>
> Cc: Dmitry Vyukov <dvyukov@...gle.com>
> ---
>  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)
>