linux-kernel - Re: [PATCH v3 26/39] arm64: mte: Add in-kernel tag fault handler

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Date:   Fri, 25 Sep 2020 13:26:02 +0200
From:   Andrey Konovalov <andreyknvl@...gle.com>
To:     Catalin Marinas <catalin.marinas@....com>
Cc:     Dmitry Vyukov <dvyukov@...gle.com>,
        Vincenzo Frascino <vincenzo.frascino@....com>,
        kasan-dev <kasan-dev@...glegroups.com>,
        Andrey Ryabinin <aryabinin@...tuozzo.com>,
        Alexander Potapenko <glider@...gle.com>,
        Marco Elver <elver@...gle.com>,
        Evgenii Stepanov <eugenis@...gle.com>,
        Elena Petrova <lenaptr@...gle.com>,
        Branislav Rankov <Branislav.Rankov@....com>,
        Kevin Brodsky <kevin.brodsky@....com>,
        Will Deacon <will.deacon@....com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        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 v3 26/39] arm64: mte: Add in-kernel tag fault handler

On Fri, Sep 25, 2020 at 12:49 PM Catalin Marinas
<catalin.marinas@....com> wrote:
>
> > diff --git a/arch/arm64/mm/fault.c b/arch/arm64/mm/fault.c
> > index a3bd189602df..d110f382dacf 100644
> > --- a/arch/arm64/mm/fault.c
> > +++ b/arch/arm64/mm/fault.c
> > @@ -33,6 +33,7 @@
> >  #include <asm/debug-monitors.h>
> >  #include <asm/esr.h>
> >  #include <asm/kprobes.h>
> > +#include <asm/mte.h>
> >  #include <asm/processor.h>
> >  #include <asm/sysreg.h>
> >  #include <asm/system_misc.h>
> > @@ -294,6 +295,11 @@ static void die_kernel_fault(const char *msg, unsigned long addr,
> >       do_exit(SIGKILL);
> >  }
> >
> > +static void report_tag_fault(unsigned long addr, unsigned int esr,
> > +                          struct pt_regs *regs)
> > +{
> > +}
>
> Do we need to introduce report_tag_fault() in this patch? It's fine but
> add a note in the commit log that it will be populated in a subsequent
> patch.

I did, see the last line of the commit description.

> > +
> >  static void __do_kernel_fault(unsigned long addr, unsigned int esr,
> >                             struct pt_regs *regs)
> >  {
> > @@ -641,10 +647,40 @@ static int do_sea(unsigned long addr, unsigned int esr, struct pt_regs *regs)
> >       return 0;
> >  }
> >
> > +static void do_tag_recovery(unsigned long addr, unsigned int esr,
> > +                        struct pt_regs *regs)
> > +{
> > +     static bool reported = false;
> > +
> > +     if (!READ_ONCE(reported)) {
> > +             report_tag_fault(addr, esr, regs);
> > +             WRITE_ONCE(reported, true);
> > +     }
>
> I don't mind the READ_ONCE/WRITE_ONCE here but not sure what they help
> with.

The fault can happen on multiple cores at the same time, right? In
that case without READ/WRITE_ONCE() we'll have a data-race here.