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SubjectRe: [PATCH] x86/intel/quark: Parameterize the kernel's IMR lock logic
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On Thu, 2016-02-18 at 19:53 +0100, Ingo Molnar wrote:
> * Bryan O'Donoghue <pure.logic@nexus-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.

I'm in favour of that too. Charitably I think locking a register like
this makes sense only when you talk about it in a meeting room
somewhere; as soon as you go to try to use it in a real situation you
find its far more trouble than its really worth.

So, I'm going to trim that out of this code unless I hear some pushback
from elsewhere in the 1/2 day or so.

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

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