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

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Date:   Mon, 19 Jun 2023 13:36:19 +0200
From:   Marco Elver <elver@...gle.com>
To:     Dmitry Vyukov <dvyukov@...gle.com>
Cc:     Chanho Min <chanho.min@....com>,
        Andrey Ryabinin <ryabinin.a.a@...il.com>,
        Alexander Potapenko <glider@...gle.com>,
        Andrey Konovalov <andreyknvl@...il.com>,
        Vincenzo Frascino <vincenzo.frascino@....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 12:15, Dmitry Vyukov <dvyukov@...gle.com> wrote:
> 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.

I think the point is that it depends on the hardware implementation of
MTE. There are a range of possibilities, but enabling KASAN_HW_TAGS
doesn't consume any extra memory for tags itself if the hardware has
to enable MTE and provision tag space via firmware to begin with.

> > Signed-off-by: Chanho Min <chanho.min@....com>

I think you just have to be a bit clearer in the commit description,
just briefly mentioning how/where the tag space is allocated in
hardware that do support MTE. Then removing this line is probably
fair, if KASAN_HW_TAGS isn't the direct reason for tag memory being
allocated.