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

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Message-ID: <20240411154007.5bdf8d95@gandalf.local.home>
Date: Thu, 11 Apr 2024 15:40:07 -0400
From: Steven Rostedt <rostedt@...dmis.org>
To: "Guilherme G. Piccoli" <gpiccoli@...lia.com>
Cc: "Luck, Tony" <tony.luck@...el.com>, Kees Cook <keescook@...omium.org>,
 Joel Fernandes <joel@...lfernandes.org>, "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 Thu, 11 Apr 2024 16:11:55 -0300
"Guilherme G. Piccoli" <gpiccoli@...lia.com> wrote:

> 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...

Great!

> 
> 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.

What I think I could do is to have a check after memory is allocated to
copy the table mapping (in the heap) if it is filled. The reason I did it
this way was because it was the easiest way to save the label to address
memory before memory is initialized. I use a __initdata array (why waste
memory if it's hardly ever used).

But, after memory is initialized, we can check if the table has content,
and if so allocate a copy and store it there and use that table instead.
That would give modules a way to find the address as well.

-- Steve