linux-kernel - Re: [patch] my mmu notifiers

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Message-ID: <20080220024944.GB11364@sgi.com>
Date:	Tue, 19 Feb 2008 20:49:44 -0600
From:	Robin Holt <holt@....com>
To:	Nick Piggin <npiggin@...e.de>
Cc:	Andrea Arcangeli <andrea@...ranet.com>, akpm@...ux-foundation.org,
	Robin Holt <holt@....com>, Avi Kivity <avi@...ranet.com>,
	Izik Eidus <izike@...ranet.com>,
	kvm-devel@...ts.sourceforge.net,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	general@...ts.openfabrics.org,
	Steve Wise <swise@...ngridcomputing.com>,
	Roland Dreier <rdreier@...co.com>,
	Kanoj Sarcar <kanojsarcar@...oo.com>, steiner@....com,
	linux-kernel@...r.kernel.org, linux-mm@...ck.org,
	daniel.blueman@...drics.com, Christoph Lameter <clameter@....com>
Subject: Re: [patch] my mmu notifiers

On Wed, Feb 20, 2008 at 12:11:57AM +0100, Nick Piggin wrote:
> On Tue, Feb 19, 2008 at 02:58:51PM +0100, Andrea Arcangeli wrote:
> > On Tue, Feb 19, 2008 at 09:43:57AM +0100, Nick Piggin wrote:
> > > anything when changing the pte to be _more_ permissive, and I don't
> > 
> > Note that in my patch the invalidate_pages in mprotect can be
> > trivially switched to a mprotect_pages with proper params. This will
> > prevent page faults completely in the secondary MMU (there will only
> > be tlb misses after the tlb flush just like for the core linux pte),
> > and it'll allow all the secondary MMU pte blocks (512/1024 at time
> > with my PT lock design) to be updated to have proper permissions
> > matching the core linux pte.
> 
> Sorry, I realise I still didn't get this through my head yet (and also
> have not seen your patch recently). So I don't know exactly what you
> are doing...
> 
> But why does _anybody_ (why does Christoph's patches) need to invalidate
> when they are going to be more permissive? This should be done lazily by
> the driver, I would have thought.

I don't believe it should, but it probably does right now.  I do know
the case where a write fault where there is no need for a COW does
not call out on the PTE change.  I see no reason the others should not
handle this as well.  Just off the top of my head, I can only think of
the mprotect case needing to special case the more permissive state and
I don't think that changes PTEs at all, merely updates the VMA.

Thanks,
Robin
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