linux-kernel - Re: [PATCH v1] ARM: A9: Add ARM ERRATA 764319 workaround

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Message-ID: <CAK8P3a1AG5RXW74LbskwMh1yJzXUjrzdL=iqaVz_7W2hExVuGw@mail.gmail.com>
Date:   Wed, 11 May 2022 14:45:27 +0200
From:   Arnd Bergmann <arnd@...db.de>
To:     "Hawkins, Nick" <nick.hawkins@....com>
Cc:     Will Deacon <will@...nel.org>, Arnd Bergmann <arnd@...db.de>,
        "Verdun, Jean-Marie" <verdun@....com>,
        Russell King - ARM Linux <linux@...linux.org.uk>,
        Mark Rutland <mark.rutland@....com>,
        Linux ARM <linux-arm-kernel@...ts.infradead.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Joel Stanley <joel@....id.au>
Subject: Re: [PATCH v1] ARM: A9: Add ARM ERRATA 764319 workaround

On Wed, May 11, 2022 at 2:23 PM Hawkins, Nick <nick.hawkins@....com> wrote:
> On Tue, May 10, 2022 at 03:01:26PM +0200, Arnd Bergmann wrote:
> > > On Tue, May 10, 2022 at 1:53 PM Verdun, Jean-Marie <verdun@....com> wrote:
> > >
> > > I got a little lost trying to find where the breakpoint instruction
> > > comes from that gets trapped here, but I would guess that they had to
> > > do this using an undef_hook because the ex_table approach does not
> > > work there for some reason.
> > >
> > > I would still pick the ex_table method here if that works.
>
> > IIRC, the ex_table handlers are called only for data aborts and are intended to be used to handle cases where we take a fault on a memory access (e.g.
> translation fault). In this case, we're taking an undefined instruction exception on a cp14 access and so the undef_hook is the right thing to use.
>
> Given Will's input would you like me to still use the ex_table method?

If it doesn't work, then there is no point trying. You could try
changing the exception
handling so it searches the ex_table for Undefined Instruction
exceptions as well,
but that's probably more complicated.

       Arnd