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From:   Dmitry Vyukov <dvyukov@google.com>
Date:   Tue, 20 Oct 2020 07:20:05 +0200
Message-ID: <CACT4Y+a=twL5eKnpZE18g4j57+PEYMPC0Loyx_mepn4u+hJTxg@mail.gmail.com>
Subject: Re: [PATCH RFC 0/8] kasan: hardware tag-based mode for production use
 on arm64
To:     Marco Elver <elver@google.com>
Cc:     Andrey Konovalov <andreyknvl@google.com>,
        Catalin Marinas <catalin.marinas@arm.com>,
        Will Deacon <will.deacon@arm.com>,
        Vincenzo Frascino <vincenzo.frascino@arm.com>,
        Alexander Potapenko <glider@google.com>,
        Evgenii Stepanov <eugenis@google.com>,
        Andrey Ryabinin <aryabinin@virtuozzo.com>,
        Elena Petrova <lenaptr@google.com>,
        Branislav Rankov <Branislav.Rankov@arm.com>,
        Kevin Brodsky <kevin.brodsky@arm.com>,
        Andrew Morton <akpm@linux-foundation.org>,
        kasan-dev <kasan-dev@googlegroups.com>,
        Linux ARM <linux-arm-kernel@lists.infradead.org>,
        Linux Memory Management List <linux-mm@kvack.org>,
        LKML <linux-kernel@vger.kernel.org>,
        Serban Constantinescu <serbanc@google.com>,
        Kostya Serebryany <kcc@google.com>
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On Mon, Oct 19, 2020 at 2:23 PM Marco Elver <elver@google.com> wrote:
>
> On Wed, 14 Oct 2020 at 22:44, Andrey Konovalov <andreyknvl@google.com> wrote:
> [...]
> > A question to KASAN maintainers: what would be the best way to support the
> > "off" mode? I see two potential approaches: add a check into each kasan
> > callback (easier to implement, but we still call kasan callbacks, even
> > though they immediately return), or add inline header wrappers that do the
> > same.
>
> This is tricky, because we don't know how bad the performance will be
> if we keep them as calls. We'd have to understand the performance
> impact of keeping them as calls, and if the performance impact is
> acceptable or not.
>
> Without understanding the performance impact, the only viable option I
> see is to add __always_inline kasan_foo() wrappers, which use the
> static branch to guard calls to __kasan_foo().

This sounds reasonable to me.