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

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Date:   Mon, 5 Aug 2019 21:52:58 -0400
From:   Luis Araneda <luaraneda@...il.com>
To:     Michal Simek <michal.simek@...inx.com>
Cc:     Russell King - ARM Linux admin <linux@...linux.org.uk>,
        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 Michal,

Thanks for the review.

On Mon, Aug 5, 2019 at 5:53 AM Michal Simek <michal.simek@...inx.com> wrote:
>
> On 31. 07. 19 6:12, Luis Araneda wrote:
> > 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.
> >
>
> There are two things together. Thanks Russel to pointing to it.
> 1. How to support SMP in thumb2 mode?
> Adding .arm mode to headsmp.S which ensure that cpu starts in proper
> mode and correct code size is copied.
> And also point to secondary_startup_arm in zynq_boot_secondary to switch
> cpu from arm to thumb mode.
>
> 2. And the second is this patch to fix FORTIFY_SOURCE.
>
> Feel free to create the first patch too or I will do it myself.

I'll be sending the two patches as a series (I already tested that
they work), so they can be picked by the stable trees.

Thanks,
Luis Araneda.