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

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Message-Id: <9F1B6537-F0BF-46E1-92A2-92C082DDB573@joelfernandes.org>
Date: Wed, 10 Apr 2024 04:11:05 +0530
From: Joel Fernandes <joel@...lfernandes.org>
To: "Luck, Tony" <tony.luck@...el.com>
Cc: Kees Cook <keescook@...omium.org>,
 Steven Rostedt <rostedt@...dmis.org>, linux-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, 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,
 "H. Peter Anvin" <hpa@...or.com>, Peter Zijlstra <peterz@...radead.org>,
 "Guilherme G. Piccoli" <gpiccoli@...lia.com>,
 linux-hardening@...r.kernel.org, Guenter Roeck <linux@...ck-us.net>,
 Ross Zwisler <zwisler@...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 Apr 10, 2024, at 3:55 AM, Luck, Tony <tony.luck@...el.com> 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.

If that were the case universally, then ramoops pstore backend would not work either?

And yet we get the last kernel logs via the pstore for many years now, on embedded-ish devices.

From my reading, ECC-enabled DRAM is not present on lots of systems and IIRC, pstore ramoops has its own ECC.

Or did I miss a recent trend with ECC-enabled DRAM?

- Joel

> 
> -Tony