Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 2620:137:e000::1:20 as permitted sender) client-ip=2620:137:e000::1:20;
MIME-Version: 1.0
References: <20230619101224.22978-1-chanho.min@lge.com> <CACT4Y+Zn49-6R00buq-y_H0qs=4gBh6PBsJDFBptL8=h6GPQYA@mail.gmail.com>
 <CANpmjNMSfVeDa-YC-RQcZ-V=wvHGi43xvXSvaR0GQkEP0OOmOQ@mail.gmail.com>
In-Reply-To: <CANpmjNMSfVeDa-YC-RQcZ-V=wvHGi43xvXSvaR0GQkEP0OOmOQ@mail.gmail.com>
From:   Andrey Konovalov <andreyknvl@gmail.com>
Date:   Tue, 20 Jun 2023 18:32:50 +0200
Message-ID: <CA+fCnZfi_o6QbfDamUjsPXjtnEwKyBn8y+T8=zxV2mEpA=DUyQ@mail.gmail.com>
Subject: Re: [PATCH] kasan: fix mention for KASAN_HW_TAGS
To:     Marco Elver <elver@google.com>, Chanho Min <chanho.min@lge.com>
Cc:     Dmitry Vyukov <dvyukov@google.com>,
        Andrey Ryabinin <ryabinin.a.a@gmail.com>,
        Alexander Potapenko <glider@google.com>,
        Vincenzo Frascino <vincenzo.frascino@arm.com>,
        kasan-dev@googlegroups.com, linux-mm@kvack.org,
        linux-kernel@vger.kernel.org, gunho.lee@lge.com
Content-Type: text/plain; charset="UTF-8"
Content-Transfer-Encoding: quoted-printable
Precedence: bulk

On Mon, Jun 19, 2023 at 1:36=E2=80=AFPM Marco Elver <elver@google.com> wrot=
e:
>
> On Mon, 19 Jun 2023 at 12:15, Dmitry Vyukov <dvyukov@google.com> wrote:
> > On Mon, 19 Jun 2023 at 12:12, Chanho Min <chanho.min@lge.com> wrote:
> > >
> > > This patch removes description of the KASAN_HW_TAGS's memory consumpt=
ion.
> > > 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.

1/32 is correct: 4 bits for every 16 bytes.

> 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.

Yeah, saying that HW_TAGS consumes memory is wrong.

But it might reasonable to spell out what happens with memory in the
config options description. Something like:

"Does not consume memory by itself but relies on the 1/32nd of
available memory being reserved by the firmware when MTE is enabled."