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

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Message-ID: <20240509163310.2aa0b2e1@rorschach.local.home>
Date: Thu, 9 May 2024 16:33:10 -0400
From: Steven Rostedt <rostedt@...dmis.org>
To: Mike Rapoport <rppt@...nel.org>
Cc: "Guilherme G. Piccoli" <gpiccoli@...lia.com>, "Luck, Tony"
 <tony.luck@...el.com>, Kees Cook <keescook@...omium.org>, Joel Fernandes
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 <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>,
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 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, 9 May 2024 23:24:20 +0300
Mike Rapoport <rppt@...nel.org> wrote:

> On Thu, May 09, 2024 at 01:31:22PM -0400, Steven Rostedt wrote:
> > On Thu, 9 May 2024 00:00:23 -0400
> > Steven Rostedt <rostedt@...dmis.org> wrote:
> >   
> > > I tried this approach and it unfortunately picks a different physical
> > > location every time :-(
> > > 
> > > So it is either adding to e820 tables or we create a new way to
> > > allocate memory at early boot up.
> > >   
> > 
> > Hmm, now I'm testing it more and it always seems to end up in the same
> > location. I'm not sure why it failed the first three times I tried it :-/  
> 
> If the kernel and the command line were the same, they shouldn't have. 
> e820 translates to memblock the same way every boot and the early
> allocations also do not change from boot to boot.
> 
> Could it be that three runs that failed had some differences in the kernel
> parameters?
> 

I wonder if KASLR caused it or not. But when I first added it to
another machine, it failed to get the same address on the second boot,
but was fine after that.

Could be just something with my setup. I'm going to backport this to
5.15 and test this on a Chromebook and see what happens there (as
that's the motivation behind this work).

-- Steve