linux-kernel - Re: [PATCH] x86/intel/quark: Parameterize the kernel's IMR lock logic

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Message-ID: <1455791503.31619.246.camel@nexus-software.ie>
Date:	Thu, 18 Feb 2016 10:31:43 +0000
From:	Bryan O'Donoghue <pure.logic@...us-software.ie>
To:	Ingo Molnar <mingo@...nel.org>
Cc:	linux-kernel@...r.kernel.org, corbet@....net, tglx@...utronix.de,
	mingo@...hat.com, hpa@...or.com, x86@...nel.org,
	andriy.shevchenko@...ux.intel.com, boon.leong.ong@...el.com,
	fengguang.wu@...el.com, linux-doc@...r.kernel.org
Subject: Re: [PATCH] x86/intel/quark: Parameterize the kernel's IMR lock
 logic

On Thu, 2016-02-18 at 08:58 +0100, Ingo Molnar wrote:
> So why not simply do the patch below? Very few people use boot
> parameters, and the 
> complexity does not seem to be worth it.
> 
> Furthermore I think an IMR range in itself is safe enough - it's not
> like such 
> register state is going to be randomly corrupted, even with the
> 'lock' bit unset. 


Hi Ingo.

I agree - to flip the lock bit you need to be in ring-0 anyway.

> So it's a perfectly fine protective measure against accidental memory
> corruption 
> from the DMA space. It should not try to be more than that.
> 
> And once we do this, I suggest we get rid of the 'lock' parameter
> altogether - 
> that will further simplify the code.
> 
> Thanks,
> 
>         Ingo

That was the V1 of this patch

https://groups.google.com/forum/#!topic/linux.kernel/6ZuVOF3TJow

Andriy asked for the boot parameter to control the state of the IMR
lock bit, I'm just as happy to go back to that version TBH