linux-kernel - Re: [PATCH v8 30/43] arm64: kasan: Allow enabling in-kernel MTE

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Date:   Thu, 5 Nov 2020 17:39:02 +0000
From:   Catalin Marinas <catalin.marinas@....com>
To:     Andrey Konovalov <andreyknvl@...gle.com>
Cc:     Will Deacon <will.deacon@....com>,
        Vincenzo Frascino <vincenzo.frascino@....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>,
        Kevin Brodsky <kevin.brodsky@....com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        kasan-dev <kasan-dev@...glegroups.com>,
        Linux ARM <linux-arm-kernel@...ts.infradead.org>,
        Linux Memory Management List <linux-mm@...ck.org>,
        LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v8 30/43] arm64: kasan: Allow enabling in-kernel MTE

On Thu, Nov 05, 2020 at 06:29:17PM +0100, Andrey Konovalov wrote:
> On Thu, Nov 5, 2020 at 6:26 PM Catalin Marinas <catalin.marinas@....com> wrote:
> >
> > On Thu, Nov 05, 2020 at 12:18:45AM +0100, Andrey Konovalov wrote:
> > > diff --git a/arch/arm64/kernel/mte.c b/arch/arm64/kernel/mte.c
> > > index 06ba6c923ab7..fcfbefcc3174 100644
> > > --- a/arch/arm64/kernel/mte.c
> > > +++ b/arch/arm64/kernel/mte.c
> > > @@ -121,6 +121,13 @@ void *mte_set_mem_tag_range(void *addr, size_t size, u8 tag)
> > >       return ptr;
> > >  }
> > >
> > > +void __init mte_init_tags(u64 max_tag)
> > > +{
> > > +     /* Enable MTE Sync Mode for EL1. */
> > > +     sysreg_clear_set(sctlr_el1, SCTLR_ELx_TCF_MASK, SCTLR_ELx_TCF_SYNC);
> > > +     isb();
> > > +}
> >
> > Is this going to be called on each CPU? I quickly went through the rest
> > of the patches and couldn't see how.
> 
> Yes, on each CPU. This is done via kasan_init_hw_tags() that is called
> from cpu_enable_mte(). This change is added in the "kasan, arm64:
> implement HW_TAGS runtime".

Ah, I got there eventually in patch 38. Too many indirections ;) (I'm
sure we could have trimmed them down a bit, hw_init_tags ==
arch_init_tags == mte_init_tags).

> Would it make sense to put it into a separate patch?

I think that's fine. I had the impression that kasan_init_hw_tags()
should only be called once.

-- 
Catalin