Re: [PATCH][RFC] mm: Introduce kernelcore=reliable option

[Matt Fleming <matt@codeblueprint.co.uk>]

On Fri, 09 Oct, at 06:51:34PM, Luck, Tony wrote:
> 
> Current hardware can map one mirrored region from each memory controller.
> We have two memory controllers per socket.  So on a 4-socket machine we will
> usually have 8 separate mirrored ranges. Two per NUMA node (assuming
> cluster on die is not enabled).
> 
> Practically I think it is safe to assume that any sane configuration will always
> choose to mirror the <4GB range:
> 
> 1) It's a trivial percentage of total memory on a system that supports mirror
> (2GB[1] out of my, essentially minimal, 512GB[2] machine). So 0.4% ... why would
> you not mirror it?
> 2) It contains a bunch of things that you are likely to want mirrored. Currently
> our boot loaders put the kernel there (don't they??). All sorts of BIOS space that
> might be accessed at any time by SMI is there.

Yeah, the bootloader and kernel image will most likely be in < 4GB
region. That's not a hard requirement, and there's certainly support
for loading things at higher addresses, but this low region is
currently still preferred (see CONFIG_PHYSICAL_START).

-- 
Matt Fleming, Intel Open Source Technology Center

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