linux-kernel - Re: [PATCH] kasan: fix mention for KASAN_HW

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Date:   Mon, 19 Jun 2023 12:14:49 +0200
From:   Dmitry Vyukov <dvyukov@...gle.com>
To:     Chanho Min <chanho.min@....com>
Cc:     Andrey Ryabinin <ryabinin.a.a@...il.com>,
        Alexander Potapenko <glider@...gle.com>,
        Andrey Konovalov <andreyknvl@...il.com>,
        Vincenzo Frascino <vincenzo.frascino@....com>,
        elver@...gle.com, kasan-dev@...glegroups.com, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org, gunho.lee@....com
Subject: Re: [PATCH] kasan: fix mention for KASAN_HW_TAGS

On Mon, 19 Jun 2023 at 12:12, Chanho Min <chanho.min@....com> wrote:
>
> This patch removes description of the KASAN_HW_TAGS's memory consumption.
> KASAN_HW_TAGS does not set 1/32nd shadow memory.

The hardware still allocates/uses shadow in MTE.
Though, it may be 1/16-th, not sure.

> Signed-off-by: Chanho Min <chanho.min@....com>
> ---
>  lib/Kconfig.kasan | 2 --
>  1 file changed, 2 deletions(-)
>
> diff --git a/lib/Kconfig.kasan b/lib/Kconfig.kasan
> index fdca89c05745..5be1740234b9 100644
> --- a/lib/Kconfig.kasan
> +++ b/lib/Kconfig.kasan
> @@ -124,8 +124,6 @@ config KASAN_HW_TAGS
>           Supported only on arm64 CPUs starting from ARMv8.5 and relies on
>           Memory Tagging Extension and Top Byte Ignore.
>
> -         Consumes about 1/32nd of available memory.
> -
>           May potentially introduce problems related to pointer casting and
>           comparison, as it embeds a tag into the top byte of each pointer.
>
> --
> 2.17.1
>