linux-kernel - Re: [PATCH 2/4] arm64: mte: Add asynchronous mode support

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Date:   Fri, 8 Jan 2021 10:48:15 +0000
From:   Vincenzo Frascino <vincenzo.frascino@....com>
To:     Andrey Konovalov <andreyknvl@...gle.com>
Cc:     Linux ARM <linux-arm-kernel@...ts.infradead.org>,
        LKML <linux-kernel@...r.kernel.org>,
        kasan-dev <kasan-dev@...glegroups.com>,
        Catalin Marinas <catalin.marinas@....com>,
        Will Deacon <will.deacon@....com>,
        Dmitry Vyukov <dvyukov@...gle.com>,
        Andrey Ryabinin <aryabinin@...tuozzo.com>,
        Alexander Potapenko <glider@...gle.com>,
        Marco Elver <elver@...gle.com>,
        Evgenii Stepanov <eugenis@...gle.com>,
        Branislav Rankov <Branislav.Rankov@....com>
Subject: Re: [PATCH 2/4] arm64: mte: Add asynchronous mode support

Hi Andrey,

On 1/7/21 7:18 PM, Andrey Konovalov wrote:
>> Boolean arguments are generally bad for legibility, hence I tend to avoid them.
>> In this case exposing the constants does not seem a big issue especially because
>> the only user of this code is "KASAN_HW_TAGS" and definitely improves its
>> legibility hence I would prefer to keep it as is.
>
> I don't like that this spills KASAN internals to the arm64 code.

Could you please elaborate a bit more on this?

If I understand it correctly these enumerations I exposed are the direct
representation of a kernel command line parameter which, according to me, should
not be considered an internal interface.
Seems that in general the kernel subsystems expose the interface for the
architectures to consume which is the same design pattern I followed in this case.

> Let's add another enum with two values and pass it as an argument then.
> Something like:
> 
> enum mte_mode {
>   ARM_MTE_SYNC,
>   ARM_MTE_ASYNC
> }

I had something similar at the beginning of the development but I ended up in a
situation in which the generic kasan code had to know about "enum mte_mode",
hence I preferred to keep kasan agnostic to the hw implementation details.

What do you think?

-- 
Regards,
Vincenzo