Re: [PATCH] kasan: fix mention for KASAN_HW_TAGS

[Andrey Konovalov]

On Mon, Jun 19, 2023 at 1:36 PM Marco Elver <elver@xxxxxxxxxx> wrote:
>
> On Mon, 19 Jun 2023 at 12:15, Dmitry Vyukov <dvyukov@xxxxxxxxxx> wrote:
> > On Mon, 19 Jun 2023 at 12:12, Chanho Min <chanho.min@xxxxxxx> 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.

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."