linux-kernel - Re: [PATCH] mte: Follow arm64.nomte override in MMU setup.

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Message-ID: <87v8r1uztz.wl-maz@kernel.org>
Date:   Tue, 09 Aug 2022 17:49:28 +0100
From:   Marc Zyngier <maz@...nel.org>
To:     Evgenii Stepanov <eugenis@...gle.com>
Cc:     Catalin Marinas <catalin.marinas@....com>,
        Will Deacon <will@...nel.org>,
        Peter Collingbourne <pcc@...gle.com>,
        Vincenzo Frascino <vincenzo.frascino@....com>,
        Andrey Konovalov <andreyknvl@...il.com>,
        Mark Brown <broonie@...nel.org>,
        Linux ARM <linux-arm-kernel@...ts.infradead.org>,
        LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] mte: Follow arm64.nomte override in MMU setup.

On Tue, 09 Aug 2022 17:41:28 +0100,
Evgenii Stepanov <eugenis@...gle.com> wrote:
> 
> On Tue, Aug 9, 2022 at 1:50 AM Marc Zyngier <maz@...nel.org> wrote:
> > How comes such memory is being used? How comes it is in the linear
> > map?
> >
> > arm64.nomte is affecting the use of MTE feature on the platform. It
> > doesn't guard the use of a MTE carve-out, and doesn't allow it to be
> > used in any shape or form.
> >
> > To use this memory, you should remove the MTE configuration
> > altogether, as you cannot infer what the CPU is doing with it.
> 
> This can be used to enable MTE in TZ but not in the NS memory.

In which case what is the tag memory doing in the linear map?
Shouldn't it be marked as reserved, not mapped, and in general
completely ignored by the NS OS?

	M.

-- 
Without deviation from the norm, progress is not possible.