linux-kernel - Re: [PATCH] x86: Add warning when memmap=nn!ss and CONFIG_RANDOMIZE

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Date:   Fri, 18 Nov 2016 12:33:35 +0100 (CET)
From:   Thomas Gleixner <tglx@...utronix.de>
To:     Dave Jiang <dave.jiang@...el.com>
cc:     Ingo Molnar <mingo@...nel.org>, "H. Peter Anvin" <hpa@...or.com>,
        dan.j.williams@...el.com, x86@...nel.org, david@...morbit.com,
        LKML <linux-kernel@...r.kernel.org>, linux-nvdimm@...1.01.org
Subject: Re: [PATCH] x86: Add warning when memmap=nn!ss and CONFIG_RANDOMIZE_BASE
 enabled

On Thu, 17 Nov 2016, Dave Jiang wrote:
> CONFIG_RANDOMIZE_BASE can place the kernel anywhere. This causes a problem
> for when memmap=nn!ss is used. This information is not known until after
> the kernel starts executing and the decision for where the randomized
> base goes happens before the kernel is uncompressed. memmap=nn!ss is not
> reliable in the presence of CONFIG_RANDOMIZE_BASE.

So this is a description of a problem. Now what's missing is a useful
explanation why you think that adding a warning will make things better.

IMNSHO adding that warning is just a pointless exercise. 

Why aren't you addressing the real issue and make the boot code parse that
option and prevent that region from being used for kernel placement?

The same issue exists for other memmap options as well, not just for that
PMEM thingy.

Thanks,

	tglx