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

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Message-ID: <c3dc208d-c604-0a45-13a4-2aa0e92a7ac7@intel.com>
Date:   Fri, 18 Nov 2016 09:47:01 -0700
From:   Dave Jiang <dave.jiang@...el.com>
To:     Thomas Gleixner <tglx@...utronix.de>
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

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On 11/18/2016 04:33 AM, Thomas Gleixner wrote:
> 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
> 

I wasn't planning to fix it because the pmem memmap option is really
only used for testing. Is it possible to parse the kernel commandline
parameters before the kernel is uncompressed?
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