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

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Date:	Thu, 18 Feb 2016 19:53:22 +0100
From:	Ingo Molnar <mingo@...nel.org>
To:	Bryan O'Donoghue <pure.logic@...us-software.ie>
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


* Bryan O'Donoghue <pure.logic@...us-software.ie> wrote:

> 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

heh ;-)

> 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

I really think it's over-engineered - especially considering that with the kernel 
lock-down removed there's no other IMR area that is really locked down - so we 
could get rid of the whole 'locked' logic that would simplify the code throughout.

Yeah, it's a nice looking hardware feature - but I don't think it's particularly 
useful in terms of extra protection.

Thanks,

	Ingo