linux-hardening - Re: [POC][RFC][PATCH 0/2] pstore/mm/x86: Add wildcard memmap to map pstore consistently

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Date: Thu, 11 Apr 2024 16:11:55 -0300
From: "Guilherme G. Piccoli" <gpiccoli@...lia.com>
To: "Luck, Tony" <tony.luck@...el.com>, Kees Cook <keescook@...omium.org>,
 Steven Rostedt <rostedt@...dmis.org>, Joel Fernandes <joel@...lfernandes.org>
Cc: "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
 "linux-trace-kernel@...r.kernel.org" <linux-trace-kernel@...r.kernel.org>,
 Masami Hiramatsu <mhiramat@...nel.org>, Mark Rutland <mark.rutland@....com>,
 Mathieu Desnoyers <mathieu.desnoyers@...icios.com>,
 Andrew Morton <akpm@...ux-foundation.org>,
 "Liam R. Howlett" <Liam.Howlett@...cle.com>, Vlastimil Babka
 <vbabka@...e.cz>, Lorenzo Stoakes <lstoakes@...il.com>,
 "linux-mm@...ck.org" <linux-mm@...ck.org>,
 Thomas Gleixner <tglx@...utronix.de>, Ingo Molnar <mingo@...hat.com>,
 Borislav Petkov <bp@...en8.de>, Dave Hansen <dave.hansen@...ux.intel.com>,
 "x86@...nel.org" <x86@...nel.org>, "H. Peter Anvin" <hpa@...or.com>,
 Peter Zijlstra <peterz@...radead.org>,
 "linux-hardening@...r.kernel.org" <linux-hardening@...r.kernel.org>,
 Guenter Roeck <linux@...ck-us.net>, Ross Zwisler <zwisler@...gle.com>,
 "wklin@...gle.com" <wklin@...gle.com>,
 Vineeth Remanan Pillai <vineeth@...byteword.org>,
 Suleiman Souhlal <suleiman@...gle.com>,
 Linus Torvalds <torvalds@...uxfoundation.org>,
 Catalin Marinas <catalin.marinas@....com>, Will Deacon <will@...nel.org>
Subject: Re: [POC][RFC][PATCH 0/2] pstore/mm/x86: Add wildcard memmap to map
 pstore consistently

On 09/04/2024 19:25, Luck, Tony wrote:
>>> I forgot to mention that this makes it trivial for any machine that doesn't
>>> clear memory on soft-reboot, to enable console ramoops (to have access to
>>> the last boot dmesg without needing serial).
>>>
>>> I tested this on a couple of my test boxes and on QEMU, and it works rather
>>> well.
>>
>> I've long wanted a "stable for this machine and kernel" memory region
>> like this for pstore. It would make testing much easier.
> 
> Which systems does this work on? I'd assume that servers (and anything
> else with ECC memory) would nuke contents while resetting ECC to clean
> state.
> 
> -Tony

Thanks Steve! Like Kees, I've been wanting a consistent way of mapping
some RAM for pstore for a while, without resorting to platform drivers
like Chromebooks do...

The idea seems very interesting and helpful, I'll test it here. My only
concern / "complain" is that it's currently only implemented for builtin
ramoops, which is not the default in many distros (like Arch, Ubuntu,
Debian). I read patch 2 (and discussion), so I think would be good to
have that builtin helper implemented upfront to allow modular usage of
ramoops.

Now, responding to Tony: Steam Deck also uses pstore/ram to store logs,
and I've tested in my AMD desktop, it does work. Seems disabling memory
retraining in BIOS (to speedup boot?) is somewhat common, not sure for
servers though. As Joel mentioned as well, quite common to use
pstore/ram in ARM embedded world.

Cheers,

Guilherme