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From:   Andrey Konovalov <andreyknvl@google.com>
Date:   Fri, 18 Sep 2020 17:45:54 +0200
Message-ID: <CAAeHK+z5pqSYJifvpLoHNe83UaJSsuR8WdBS8-JOwgCeHTi8ow@mail.gmail.com>
Subject: Re: [PATCH v2 21/37] kasan: introduce CONFIG_KASAN_HW_TAGS
To:     Marco Elver <elver@google.com>
Cc:     Dmitry Vyukov <dvyukov@google.com>,
        Vincenzo Frascino <vincenzo.frascino@arm.com>,
        Catalin Marinas <catalin.marinas@arm.com>,
        kasan-dev <kasan-dev@googlegroups.com>,
        Andrey Ryabinin <aryabinin@virtuozzo.com>,
        Alexander Potapenko <glider@google.com>,
        Evgenii Stepanov <eugenis@google.com>,
        Elena Petrova <lenaptr@google.com>,
        Branislav Rankov <Branislav.Rankov@arm.com>,
        Kevin Brodsky <kevin.brodsky@arm.com>,
        Will Deacon <will.deacon@arm.com>,
        Andrew Morton <akpm@linux-foundation.org>,
        Linux ARM <linux-arm-kernel@lists.infradead.org>,
        Linux Memory Management List <linux-mm@kvack.org>,
        LKML <linux-kernel@vger.kernel.org>
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On Fri, Sep 18, 2020 at 5:36 PM Marco Elver <elver@google.com> wrote:
>
> > > How about something like the below change (introduce KASAN_INSTRUMENTED
> > > Kconfig var) to avoid the repeated "KASAN_GENERIC || KASAN_SW_TAGS".
> > > This could then also be used in the various .c/.h files (and make some
> > > of the code more readable hopefully).
> >
> > I tried doing that initially, but it didn't really look good. The
> > reason is that we actually have two properties that are currently
> > common for the software modes, but aren't actually tied to each other:
> > instrumentation and shadow memory. Therefore we will end up with two
> > new configs: KASAN_INSTRUMENTED and KASAN_USES_SHADOW (or something),
> > and things get quite confusing. I think it's better to keep
> > KASAN_GENERIC || KASAN_SW_TAGS everywhere.
>
> Ah, I see. So in some cases the reason the #ifdef exists is because of
> instrumentation, in other cases because there is some shadow memory
> (right?).

Correct.

> The only other option I see is to call it what it is ("KASAN_SW" or
> "KASAN_SOFTWARE"), but other than that, I don't mind if it stays
> as-is.

Let's leave it as is then. I don't think the code will get much better
in terms of readability if we add KASAN_SOFTWARE, but we'll get
another "indirect" config option, which makes things a bit more
confusing.