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Date: Tue, 9 Apr 2024 19:14:15 -0400
From: Steven Rostedt <rostedt@goodmis.org>
To: Kees Cook <keescook@chromium.org>
Cc: 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>, Tony Luck
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 linux-hardening@vger.kernel.org, Guenter Roeck <linux@roeck-us.net>, Ross
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 Suleiman Souhlal <suleiman@google.com>, Linus Torvalds
 <torvalds@linuxfoundation.org>, Catalin Marinas <catalin.marinas@arm.com>,
 Will Deacon <will@kernel.org>
Subject: Re: [POC][RFC][PATCH 2/2] pstore/ramoops: Add ramoops.mem_name=
 command line option
Message-ID: <20240409191415.5a7b445f@gandalf.local.home>
In-Reply-To: <202404091514.B97720B8@keescook>
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	<20240409211351.234897475@goodmis.org>
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On Tue, 9 Apr 2024 15:18:45 -0700
Kees Cook <keescook@chromium.org> wrote:

> > @@ -914,6 +919,19 @@ static void __init ramoops_register_dummy(void)
> >  {
> >  	struct ramoops_platform_data pdata;
> >  
> > +#ifndef MODULE
> > +	/* Only allowed when builtin */  
> 
> Why only when builtin?

Well, because the memory table that maps the found physical memory to a
lable is marked as __initdata, and will not be available after boot. If you
wanted it for a module, you would need some builtin code to find it.

> 
> > +	if (mem_name) {
> > +		u64 start;
> > +		u64 size;
> > +
> > +		if (memmap_named(mem_name, &start, &size)) {
> > +			mem_address = start;
> > +			mem_size = size;
> > +		}
> > +	}
> > +#endif  
> 
> Otherwise this looks good, though I'd prefer some comments about what's
> happening here.
> 
> (And in retrospect, separately, I probably need to rename "dummy" to
> "commandline" or something, since it's gathering valid settings here...)

Yeah, that was a bit confusing. I kept thinking "is this function stable?".

-- Steve