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

From: Andrey Konovalov <andreyknvl@google.com>
To: Catalin Marinas <catalin.marinas@arm.com>
Cc: Dmitry Vyukov <dvyukov@google.com>,
	Vincenzo Frascino <vincenzo.frascino@arm.com>,
	 kasan-dev <kasan-dev@googlegroups.com>,
	Andrey Ryabinin <aryabinin@virtuozzo.com>,
	 Alexander Potapenko <glider@google.com>,
	Marco Elver <elver@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>
Subject: Re: [PATCH v3 26/39] arm64: mte: Add in-kernel tag fault handler
Date: Fri, 25 Sep 2020 13:26:02 +0200	[thread overview]
Message-ID: <CAAeHK+zLFRgR9eiLNyn7-iqbXJe6HGYpHYbBXXOVqOk4MyrhAA@mail.gmail.com> (raw)
In-Reply-To: <20200925104933.GD4846@gaia>

On Fri, Sep 25, 2020 at 12:49 PM Catalin Marinas
<catalin.marinas@arm.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.