linux-kernel - Re: [PATCH] pstore/ram: Clarify resource reservation labels

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Date:   Thu, 18 Oct 2018 13:31:15 -0700
From:   Kees Cook <keescook@...omium.org>
To:     Dan Williams <dan.j.williams@...el.com>
Cc:     Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Anton Vorontsov <anton@...msg.org>,
        Colin Cross <ccross@...roid.com>,
        "Luck, Tony" <tony.luck@...el.com>,
        Joel Fernandes <joel@...lfernandes.org>, zwisler@...gle.com
Subject: Re: [PATCH] pstore/ram: Clarify resource reservation labels

On Thu, Oct 18, 2018 at 8:33 AM, Dan Williams <dan.j.williams@...el.com> wrote:
> [ add Ross ]

Hi Ross! :)

> On Thu, Oct 18, 2018 at 12:15 AM Kees Cook <keescook@...omium.org> wrote:
>> As for nvdimm specifically, yes, I'd love to get pstore hooked up
>> correctly to nvdimm. How do the namespaces work? Right now pstore
>> depends one of platform driver data, device tree specification, or
>> manual module parameters.
>
> From the userspace side we have the ndctl utility to wrap
> personalities on top of namespaces. So for example, I envision we
> would be able to do:
>
>     ndctl create-namespace --mode=pstore --size=128M
>
> ...and create a small namespace that will register with the pstore sub-system.
>
> On the kernel side this would involve registering a 'pstore_dev' child
> / seed device under each region device. The 'seed-device' sysfs scheme
> is described in our documentation [1]. The short summary is ndctl
> finds a seed device assigns a namespace to it and then binding that
> device to a driver causes it to be initialized by the kernel.
>
> [1]: https://www.kernel.org/doc/Documentation/nvdimm/nvdimm.txt

Interesting!

Really, this would be a way to configure "ramoops" (the persistent RAM
backend to pstore), rather than pstore itself (pstore is just the
framework). From reading the ndctl man page it sounds like there isn't
a way to store configuration information beyond just size?

ramoops will auto-configure itself and fill available space using its
default parameters, but it might be nice to have a way to store that
somewhere (traditionally it's part of device tree or platform data).
ramoops could grow a "header", but normally the regions are very small
so I've avoided that.

I'm not sure I understand the right way to glue ramoops_probe() to the
"seed-device" stuff. (It needs to be probed VERY early to catch early
crashes -- ramoops uses postcore_initcall() normally.)

Thanks for the pointers!

-Kees

-- 
Kees Cook
Pixel Security