linux-kernel - Re: [PATCH] pstore/ram: Improve backward compatibility with older Chromebooks

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Date:   Tue, 7 May 2019 15:17:38 -0700
From:   Frank Rowand <frowand.list@...il.com>
To:     Doug Anderson <dianders@...omium.org>,
        Kees Cook <keescook@...omium.org>
Cc:     Rob Herring <robh@...nel.org>, Anton Vorontsov <anton@...msg.org>,
        "open list:ARM/Rockchip SoC..." <linux-rockchip@...ts.infradead.org>,
        Julius Werner <jwerner@...omium.org>,
        Guenter Roeck <groeck@...omium.org>,
        Matthias Kaehlcke <mka@...omium.org>,
        Brian Norris <briannorris@...omium.org>,
        Colin Cross <ccross@...roid.com>,
        Tony Luck <tony.luck@...el.com>,
        LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] pstore/ram: Improve backward compatibility with older
 Chromebooks

On 5/6/19 4:58 PM, Doug Anderson wrote:
> Hi,
> 
> On Mon, May 6, 2019 at 2:10 PM Kees Cook <keescook@...omium.org> wrote:
>>
>> From: Douglas Anderson <dianders@...omium.org>
>> Date: Fri, May 3, 2019 at 10:48 AM
>> To: Kees Cook, Anton Vorontsov
>> Cc: <linux-rockchip@...ts.infradead.org>, <jwerner@...omium.org>,
>> <groeck@...omium.org>, <mka@...omium.org>, <briannorris@...omium.org>,
>> Douglas Anderson, Colin Cross, Tony Luck,
>> <linux-kernel@...r.kernel.org>
>>
>>> When you try to run an upstream kernel on an old ARM-based Chromebook
>>> you'll find that console-ramoops doesn't work.
>>>
>>> Old ARM-based Chromebooks, before <https://crrev.com/c/439792>
>>> ("ramoops: support upstream {console,pmsg,ftrace}-size properties")
>>> used to create a "ramoops" node at the top level that looked like:
>>>
>>> / {
>>>   ramoops {
>>>     compatible = "ramoops";
>>>     reg = <...>;
>>>     record-size = <...>;
>>>     dump-oops;
>>>   };
>>> };
>>>
>>> ...and these Chromebooks assumed that the downstream kernel would make
>>> console_size / pmsg_size match the record size.  The above ramoops
>>> node was added by the firmware so it's not easy to make any changes.
>>>
>>> Let's match the expected behavior, but only for those using the old
>>> backward-compatible way of working where ramoops is right under the
>>> root node.
>>>
>>> NOTE: if there are some out-of-tree devices that had ramoops at the
>>> top level, left everything but the record size as 0, and somehow
>>> doesn't want this behavior, we can try to add more conditions here.
>>>
>>> Signed-off-by: Douglas Anderson <dianders@...omium.org>
>>
>> I like this; thanks! Rob is this okay by you? I just want to
>> double-check since it's part of the DT parsing logic.
>>
>> I'll pick it up and add a Cc: stable.
> 
> Hold off a second--I may need to send out a v2 but out of time for the
> day.  I think I need a #include file to fix errors on x86:
> 
>> implicit declaration of function 'of_node_is_root' [-Werror,-Wimplicit-function-declaration

Instead of checking "of_node_is_root(parent_node)" the patch could check
for parent_node not "/reserved-memory".  Then the x86 error would not
occur.

The check I am suggesting is not as precise, but it should be good enough
for this case, correct?

-Frank

> 
> I'm unfortunately out of time for now, but I'll post a v2 within the next day.
> 
> 
> -Doug
>