Date: Tue, 5 Feb 2008 06:25:25 +0100
From: Andrea Arcangeli <andrea@qumranet.com>
To: Christoph Lameter <clameter@sgi.com>
Cc: Robin Holt <holt@sgi.com>, Avi Kivity <avi@qumranet.com>,
       Izik Eidus <izike@qumranet.com>, kvm-devel@lists.sourceforge.net,
       Peter Zijlstra <a.p.zijlstra@chello.nl>, steiner@sgi.com,
       linux-kernel@vger.kernel.org, linux-mm@kvack.org,
       daniel.blueman@quadrics.com
Subject: Re: [PATCH] mmu notifiers #v5
Message-ID: <20080205052525.GD7441@v2.random>
References: <20080131045750.855008281@sgi.com> <20080131171806.GN7185@v2.random> <Pine.LNX.4.64.0801311207540.25477@schroedinger.engr.sgi.com> <Pine.LNX.4.64.0801311508080.23624@schroedinger.engr.sgi.com> <20080131234101.GS7185@v2.random> <Pine.LNX.4.64.0801311738570.24297@schroedinger.engr.sgi.com> <20080201120955.GX7185@v2.random> <Pine.LNX.4.64.0802011118060.18163@schroedinger.engr.sgi.com> <20080203021704.GC7185@v2.random> <Pine.LNX.4.64.0802041106370.9656@schroedinger.engr.sgi.com>
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On Mon, Feb 04, 2008 at 11:09:01AM -0800, Christoph Lameter wrote:
> On Sun, 3 Feb 2008, Andrea Arcangeli wrote:
> 
> > > Right but that pin requires taking a refcount which we cannot do.
> > 
> > GRU can use my patch without the pin. XPMEM obviously can't use my
> > patch as my invalidate_page[s] are under the PT lock (a feature to fit
> > GRU/KVM in the simplest way), this is why an incremental patch adding
> > invalidate_range_start/end would be required to support XPMEM too.
> 
> Doesnt the kernel in some situations release the page before releasing the 
> pte lock? Then there will be an external pte pointing to a page that may 
> now have a different use. Its really bad if that pte does allow writes.

Sure the kernel does that most of the time, which is for example why I
had to use invalidate_page instead of invalidate_pages inside
zap_pte_range. Zero problems with that (this is also the exact reason
why I mentioned the tlb flushing code would need changes to convert
some page in pages).
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