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From: Joel Fernandes <joel@joelfernandes.org>
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Subject: Re: [POC][RFC][PATCH 0/2] pstore/mm/x86: Add wildcard memmap to map pstore consistently
Date: Wed, 10 Apr 2024 04:11:05 +0530
Message-Id: <9F1B6537-F0BF-46E1-92A2-92C082DDB573@joelfernandes.org>
References: <SJ1PR11MB608317E066B6B3390F55FCB1FC072@SJ1PR11MB6083.namprd11.prod.outlook.com>
Cc: Kees Cook <keescook@chromium.org>,
 Steven Rostedt <rostedt@goodmis.org>, linux-kernel@vger.kernel.org,
 linux-trace-kernel@vger.kernel.org, Masami Hiramatsu <mhiramat@kernel.org>,
 Mark Rutland <mark.rutland@arm.com>,
 Mathieu Desnoyers <mathieu.desnoyers@efficios.com>,
 Andrew Morton <akpm@linux-foundation.org>,
 "Liam R. Howlett" <Liam.Howlett@oracle.com>,
 Vlastimil Babka <vbabka@suse.cz>, Lorenzo Stoakes <lstoakes@gmail.com>,
 linux-mm@kvack.org, Thomas Gleixner <tglx@linutronix.de>,
 Ingo Molnar <mingo@redhat.com>, Borislav Petkov <bp@alien8.de>,
 Dave Hansen <dave.hansen@linux.intel.com>, x86@kernel.org,
 "H. Peter Anvin" <hpa@zytor.com>, Peter Zijlstra <peterz@infradead.org>,
 "Guilherme G. Piccoli" <gpiccoli@igalia.com>,
 linux-hardening@vger.kernel.org, Guenter Roeck <linux@roeck-us.net>,
 Ross Zwisler <zwisler@google.com>, wklin@google.com,
 Vineeth Remanan Pillai <vineeth@bitbyteword.org>,
 Suleiman Souhlal <suleiman@google.com>,
 Linus Torvalds <torvalds@linuxfoundation.org>,
 Catalin Marinas <catalin.marinas@arm.com>, Will Deacon <will@kernel.org>
In-Reply-To: <SJ1PR11MB608317E066B6B3390F55FCB1FC072@SJ1PR11MB6083.namprd11.prod.outlook.com>
To: "Luck, Tony" <tony.luck@intel.com>


> On Apr 10, 2024, at 3:55=E2=80=AFAM, Luck, Tony <tony.luck@intel.com> wrot=
e:
>=20
> =EF=BB=BF
>>=20
>>> I forgot to mention that this makes it trivial for any machine that does=
n't
>>> clear memory on soft-reboot, to enable console ramoops (to have access t=
o
>>> the last boot dmesg without needing serial).
>>>=20
>>> I tested this on a couple of my test boxes and on QEMU, and it works rat=
her
>>> well.
>>=20
>> I've long wanted a "stable for this machine and kernel" memory region
>> like this for pstore. It would make testing much easier.
>=20
> 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 wor=
k either?

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

=46rom my reading, ECC-enabled DRAM is not present on lots of systems and II=
RC, pstore ramoops has its own ECC.

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

- Joel


>=20
> -Tony