linux-kernel - Re: [PATCH mm v3 28/38] kasan, page_alloc: allow skipping memory init for HW

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Message-ID: <Ybjbw5iPg2BWsgqF@elver.google.com>
Date:   Tue, 14 Dec 2021 19:00:35 +0100
From:   Marco Elver <elver@...gle.com>
To:     andrey.konovalov@...ux.dev
Cc:     Alexander Potapenko <glider@...gle.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Andrey Konovalov <andreyknvl@...il.com>,
        Dmitry Vyukov <dvyukov@...gle.com>,
        Andrey Ryabinin <ryabinin.a.a@...il.com>,
        kasan-dev@...glegroups.com, linux-mm@...ck.org,
        Vincenzo Frascino <vincenzo.frascino@....com>,
        Catalin Marinas <catalin.marinas@....com>,
        Will Deacon <will@...nel.org>,
        Mark Rutland <mark.rutland@....com>,
        linux-arm-kernel@...ts.infradead.org,
        Peter Collingbourne <pcc@...gle.com>,
        Evgenii Stepanov <eugenis@...gle.com>,
        linux-kernel@...r.kernel.org,
        Andrey Konovalov <andreyknvl@...gle.com>
Subject: Re: [PATCH mm v3 28/38] kasan, page_alloc: allow skipping memory
 init for HW_TAGS

On Mon, Dec 13, 2021 at 10:54PM +0100, andrey.konovalov@...ux.dev wrote:
> From: Andrey Konovalov <andreyknvl@...gle.com>
> 
> Add a new GFP flag __GFP_SKIP_ZERO that allows to skip memory
> initialization. The flag is only effective with HW_TAGS KASAN.
[...]
> - * is being zeroed (either via __GFP_ZERO or via init_on_alloc).
> + * is being zeroed (either via __GFP_ZERO or via init_on_alloc, provided that
> + * __GFP_SKIP_ZERO is not set).
> + *
> + * %__GFP_SKIP_ZERO makes page_alloc skip zeroing memory.
> + * Only effective when HW_TAGS KASAN is enabled.
>   *
>   * %__GFP_SKIP_KASAN_UNPOISON makes KASAN skip unpoisoning on page allocation.
>   * Only effective in HW_TAGS mode.
> @@ -242,6 +247,7 @@ struct vm_area_struct;
>  #define __GFP_COMP	((__force gfp_t)___GFP_COMP)
>  #define __GFP_ZERO	((__force gfp_t)___GFP_ZERO)
>  #define __GFP_ZEROTAGS	((__force gfp_t)___GFP_ZEROTAGS)
> +#define __GFP_SKIP_ZERO ((__force gfp_t)___GFP_SKIP_ZERO)
>  #define __GFP_SKIP_KASAN_UNPOISON ((__force gfp_t)___GFP_SKIP_KASAN_UNPOISON)
>  #define __GFP_SKIP_KASAN_POISON   ((__force gfp_t)___GFP_SKIP_KASAN_POISON)
>  
> @@ -249,7 +255,7 @@ struct vm_area_struct;
>  #define __GFP_NOLOCKDEP ((__force gfp_t)___GFP_NOLOCKDEP)
>  
>  /* Room for N __GFP_FOO bits */
> -#define __GFP_BITS_SHIFT (26 + IS_ENABLED(CONFIG_LOCKDEP))
> +#define __GFP_BITS_SHIFT (27 + IS_ENABLED(CONFIG_LOCKDEP))

You're adding several new flags, I think you should also make a
corresponding change to include/trace/events/mmflags.h?

At least __GFP_SKIP_KASAN_POISON is currently in there.