Date:   Tue, 14 Dec 2021 19:00:35 +0100
From:   Marco Elver <elver@google.com>
To:     andrey.konovalov@linux.dev
Cc:     Alexander Potapenko <glider@google.com>,
        Andrew Morton <akpm@linux-foundation.org>,
        Andrey Konovalov <andreyknvl@gmail.com>,
        Dmitry Vyukov <dvyukov@google.com>,
        Andrey Ryabinin <ryabinin.a.a@gmail.com>,
        kasan-dev@googlegroups.com, linux-mm@kvack.org,
        Vincenzo Frascino <vincenzo.frascino@arm.com>,
        Catalin Marinas <catalin.marinas@arm.com>,
        Will Deacon <will@kernel.org>,
        Mark Rutland <mark.rutland@arm.com>,
        linux-arm-kernel@lists.infradead.org,
        Peter Collingbourne <pcc@google.com>,
        Evgenii Stepanov <eugenis@google.com>,
        linux-kernel@vger.kernel.org,
        Andrey Konovalov <andreyknvl@google.com>
Subject: Re: [PATCH mm v3 28/38] kasan, page_alloc: allow skipping memory
 init for HW_TAGS
Message-ID: <Ybjbw5iPg2BWsgqF@elver.google.com>
References: <cover.1639432170.git.andreyknvl@google.com>
 <cd8667450f7a0daf6b4081276e11a5f7bed60128.1639432170.git.andreyknvl@google.com>
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On Mon, Dec 13, 2021 at 10:54PM +0100, andrey.konovalov@linux.dev wrote:
> From: Andrey Konovalov <andreyknvl@google.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.