Subject: Re: [kvm-devel] [PATCH] export notifier #1
From: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Reply-To: benh@kernel.crashing.org
To: Christoph Lameter <clameter@sgi.com>
Cc: Andrea Arcangeli <andrea@qumranet.com>, Avi Kivity <avi@qumranet.com>,
       Izik Eidus <izike@qumranet.com>, Andrew Morton <akpm@osdl.org>,
       Nick Piggin <npiggin@suse.de>, kvm-devel@lists.sourceforge.net,
       steiner@sgi.com, linux-kernel@vger.kernel.org, linux-mm@kvack.org,
       daniel.blueman@quadrics.com, holt@sgi.com,
       Hugh Dickins <hugh@veritas.com>
In-Reply-To: <Pine.LNX.4.64.0801221232040.28197@schroedinger.engr.sgi.com>
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Date: Wed, 23 Jan 2008 10:36:29 +1100
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On Tue, 2008-01-22 at 12:34 -0800, Christoph Lameter wrote:
> 
> - Notifiers are called *after* we tore down ptes. At that point pages
>   may already have been freed and reused. This means that there can
>   still be uses of the page by the user of mmu_ops after the OS has
>   dropped its mapping. IMHO the foreign entity needs to drop its
>   mappings first. That also ensures that the entities operated
>   upon continue to exist.

That's definitely an issue. Maybe having the foreign entity get a
reference to the page and drop it when it unmaps would help ?

> - anon_vma/inode and pte locks are held during callbacks.

So how does that fix the problem of sleeping then ?

Ben.


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