Re: [PATCH 1/2] mm/memblock: Add "reserve_mem" to reserved named memory at boot up

[Steven Rostedt <rostedt@goodmis.org>]

On Mon, 03 Jun 2024 22:52:37 -0700
Kees Cook <kees@kernel.org> wrote:

> On June 3, 2024 4:33:31 PM PDT, Steven Rostedt <rostedt@goodmis.org> 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 layout is not the
> >same, add a new option to the kernel command line called "reserve_mem".
> >
> >The format is:  reserve_mem=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:
> >
> >  reserve_mem=12M:4096:oops ramoops.mem_name=oops  
> 
> How does this interact with KASLR? It has chosen its physical location
> before this parsing happens, so I'd expect this to fail once in a while,
> unless the size/alignment is lucky enough that KASLR never uses that
> portion of the physical memory...
> 

From looking at the KASLR code, it looks to me that it picks from 100
different locations. I could be wrong, but if you have sufficient memory,
I'm thinking that it should not conflict. But if it does, yes, it will fail
to pick the same location.

-- Steve