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Date: Tue, 9 Apr 2024 15:23:07 -0700
From: Kees Cook <keescook@chromium.org>
To: Steven Rostedt <rostedt@goodmis.org>
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Subject: Re: [POC][RFC][PATCH 1/2] mm/x86: Add wildcard * option as
 memmap=nn*align:name
Message-ID: <202404091521.B63E85D@keescook>
References: <20240409210254.660888920@goodmis.org>
 <20240409211351.075320273@goodmis.org>
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On Tue, Apr 09, 2024 at 05:02:55PM -0400, Steven Rostedt wrote:
> From: "Steven Rostedt (Google)" <rostedt@goodmis.org>
> 
> In order to allow for requesting a memory region that can be used for
> things like pstore on multiple machines where the memory is not the same,
> add a new option to the memmap=nn$ kernel command line.
> 
> The memmap=nn$addr will reserve nn amount of memory at the physical
> address addr. To use this, one must know the physical memory layout and
> know where usable memory exists in the physical layout.
> 
> Add a '*' option that will assign memory by looking for a range that can
> fit the given size and alignment. It will start at the high addresses, and
> then work its way down.
> 
> The format is:  memmap=nn*align:name
> 
> Where it will find nn amount of memory at the given alignment of align.
> The name field is to allow another subsystem to retrieve where the memory
> was found. For example:
> 
>   memmap=12M*4096:oops ramoops.mem_name=oops
> 
> Where ramoops.mem_name will tell ramoops that memory was reserved for it
> via the wildcard '*' option and it can find it by calling:
> 
>   if (memmap_named("oops", &start, &size)) {
> 	// start holds the start address and size holds the size given
> 
> Signed-off-by: Steven Rostedt (Google) <rostedt@goodmis.org>
> ---
>  arch/x86/kernel/e820.c | 91 ++++++++++++++++++++++++++++++++++++++++++
>  include/linux/mm.h     |  2 +
>  mm/memory.c            |  7 ++++
>  3 files changed, 100 insertions(+)

Do we need to involve e820 at all? I think it might be possible to just
have pstore call request_mem_region() very early? Or does KASLR make
that unstable?

-- 
Kees Cook