linux-kernel - Re: [RFC PATCH] ARM: zynq: Use memcpy_toio instead of memcpy on smp bring-up

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Message-ID: <CAHbBuxoMBiq23Rkt7-jm42O4ePY=23ZsgNEVf3UJKQ2Dg+3fbg@mail.gmail.com>
Date:   Wed, 31 Jul 2019 00:12:11 -0400
From:   Luis Araneda <luaraneda@...il.com>
To:     Russell King - ARM Linux admin <linux@...linux.org.uk>
Cc:     Michal Simek <michal.simek@...inx.com>,
        linux-arm-kernel <linux-arm-kernel@...ts.infradead.org>,
        linux-kernel@...r.kernel.org
Subject: Re: [RFC PATCH] ARM: zynq: Use memcpy_toio instead of memcpy on smp bring-up

Hi Russell,

Thanks for reviewing.

On Tue, Jul 30, 2019 at 6:47 AM Russell King - ARM Linux admin
<linux@...linux.org.uk> wrote:
>
> On Tue, Jul 30, 2019 at 12:43:26AM -0400, Luis Araneda wrote:
> > This fixes a kernel panic (read overflow) on memcpy when
> > FORTIFY_SOURCE is enabled.
[...]
>
> I'm not convinced that this is correct.  It looks like
> zynq_secondary_trampoline could be either ARM or Thumb code - there is
> no .arm directive before it.  If it's ARM code, then this is fine.  If
> Thumb code, then zynq_secondary_trampoline will be offset by one, and
> we will miss copying the first byte of code.

You're right, I tested what happens if the zynq_secondary_trampoline
is ARM or Thumb by editing the file where it's defined, headsmp.S

When the .arm directive is used, the CPU is brought-up correctly,
but if I use .thumb, I get the following message (no panic):
> CPU1: failed to come online

This seems unrelated to solving the panic, as the message
even appears with memcpy and FORTIFY_SOURCE disabled.

I could add the .arm directive to headsmp.S
Is that your expected solution?
Should that change be on a separate commit?

I'd like to know Michal's opinion, as he wrote the code.