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

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Message-ID: <20151012103235.GB2579@codeblueprint.co.uk>
Date:	Mon, 12 Oct 2015 11:32:35 +0100
From:	Matt Fleming <matt@...eblueprint.co.uk>
To:	"Luck, Tony" <tony.luck@...el.com>
Cc:	"Hansen, Dave" <dave.hansen@...el.com>,
	Xishi Qiu <qiuxishi@...wei.com>,
	Kamezawa Hiroyuki <kamezawa.hiroyu@...fujitsu.com>,
	Taku Izumi <izumi.taku@...fujitsu.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"linux-mm@...ck.org" <linux-mm@...ck.org>,
	"mel@....ul.ie" <mel@....ul.ie>,
	"akpm@...ux-foundation.org" <akpm@...ux-foundation.org>,
	Mel Gorman <mgorman@...e.de>, Ingo Molnar <mingo@...nel.org>,
	"zhongjiang@...wei.com" <zhongjiang@...wei.com>
Subject: Re: [PATCH][RFC] mm: Introduce kernelcore=reliable option

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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