linux-kernel - Re: [PATCH v9 1/4] arm64: mte: implement CONFIG_ARM64_MTE

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Date:   Wed, 13 Dec 2023 12:16:05 +0000
From:   Will Deacon <will@...nel.org>
To:     Catalin Marinas <catalin.marinas@....com>
Cc:     Alexander Potapenko <glider@...gle.com>, pcc@...gle.com,
        andreyknvl@...il.com, andriy.shevchenko@...ux.intel.com,
        aleksander.lobakin@...el.com, linux@...musvillemoes.dk,
        yury.norov@...il.com, alexandru.elisei@....com,
        linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
        eugenis@...gle.com, syednwaris@...il.com, william.gray@...aro.org
Subject: Re: [PATCH v9 1/4] arm64: mte: implement CONFIG_ARM64_MTE_COMP

On Tue, Dec 12, 2023 at 05:16:15PM +0000, Catalin Marinas wrote:
> On Mon, Nov 13, 2023 at 11:52:30AM +0100, Alexander Potapenko wrote:
> > The config implements the algorithm compressing memory tags for ARM MTE
> > during swapping.
> > 
> > The algorithm is based on RLE and specifically targets buffers of tags
> > corresponding to a single page. In many cases a buffer can be compressed
> > into 63 bits, making it possible to store it without additional memory
> > allocation.
> > 
> > Suggested-by: Evgenii Stepanov <eugenis@...gle.com>
> > Signed-off-by: Alexander Potapenko <glider@...gle.com>
> 
> Acked-by: Catalin Marinas <catalin.marinas@....com>
> 
> > +void mte_tags_to_ranges(u8 *tags, u8 *out_tags, unsigned short *out_sizes,
> > +			size_t *out_len)
> > +{
> [...]
> > +}
> > +EXPORT_SYMBOL_NS(mte_tags_to_ranges, MTECOMP);
> 
> I may have asked before, what the reason for EXPORT_SYMBOL_NS? Is it for
> the kunit tests? Otherwise we don't expect those to be accessed from
> modules.

It looks like it. The Kconfig option for the test is tristate and it calls
this symbol directly.

Will