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 <20210308165847.GF15644@arm.com>
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From:   Andrey Konovalov <andreyknvl@google.com>
Date:   Tue, 9 Mar 2021 14:09:21 +0100
Message-ID: <CAAeHK+yaHufdycvawHAQ-Lt9GHKrGkzKkdJnTA3qN1MTtwiS5g@mail.gmail.com>
Subject: Re: [PATCH v2 1/5] arm64: kasan: allow to init memory when setting tags
To:     Catalin Marinas <catalin.marinas@arm.com>
Cc:     Vincenzo Frascino <vincenzo.frascino@arm.com>,
        Alexander Potapenko <glider@google.com>,
        Marco Elver <elver@google.com>,
        Andrew Morton <akpm@linux-foundation.org>,
        Will Deacon <will.deacon@arm.com>,
        Dmitry Vyukov <dvyukov@google.com>,
        Andrey Ryabinin <aryabinin@virtuozzo.com>,
        Peter Collingbourne <pcc@google.com>,
        Evgenii Stepanov <eugenis@google.com>,
        Branislav Rankov <Branislav.Rankov@arm.com>,
        Kevin Brodsky <kevin.brodsky@arm.com>,
        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>
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On Mon, Mar 8, 2021 at 5:58 PM Catalin Marinas <catalin.marinas@arm.com> wrote:
>
> On Mon, Mar 08, 2021 at 04:55:14PM +0100, Andrey Konovalov wrote:
> > @@ -68,10 +69,16 @@ static inline void mte_set_mem_tag_range(void *addr, size_t size, u8 tag)
> >                * 'asm volatile' is required to prevent the compiler to move
> >                * the statement outside of the loop.
> >                */
> > -             asm volatile(__MTE_PREAMBLE "stg %0, [%0]"
> > -                          :
> > -                          : "r" (curr)
> > -                          : "memory");
> > +             if (init)
> > +                     asm volatile(__MTE_PREAMBLE "stzg %0, [%0]"
> > +                                  :
> > +                                  : "r" (curr)
> > +                                  : "memory");
> > +             else
> > +                     asm volatile(__MTE_PREAMBLE "stg %0, [%0]"
> > +                                  :
> > +                                  : "r" (curr)
> > +                                  : "memory");
> >
> >               curr += MTE_GRANULE_SIZE;
> >       } while (curr != end);
>
> Is 'init' always a built-in constant here? If not, checking it once
> outside the loop may be better (or check the code generation, maybe the
> compiler is smart enough).

I think it's worth moving the init check outside the loop anyway. Will do in v3.

Thanks!