linux-kernel - Re: mmu_notifier: close hole in fork

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Message-ID: <Pine.LNX.4.64.0801311745080.24297@schroedinger.engr.sgi.com>
Date:	Thu, 31 Jan 2008 17:48:19 -0800 (PST)
From:	Christoph Lameter <clameter@....com>
To:	Andrea Arcangeli <andrea@...ranet.com>
cc:	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>, steiner@....com,
	linux-kernel@...r.kernel.org, linux-mm@...ck.org,
	daniel.blueman@...drics.com
Subject: Re: mmu_notifier: close hole in fork

On Fri, 1 Feb 2008, Andrea Arcangeli wrote:

> Good catch! This was missing also in my #v5 (KVM doesn't need that
> because the only possible cows on sptes can be generated by ksm, but
> it would have been a problem for GRU). The more I think about it, the

How do you think the GRU should know when to drop the refcount? There is 
no page table and thus no way of tracking that a refcount was taken. 
Without the refcount you cannot defer the freeing of the page. So 
shootdown on invalidate_range_begin and lock out until 
invalidate_range_end seems to be the only workable solution.

BTW what do you think about adding a flag parameter to the invalidate 
calls that allows shooting down writable ptes only? That could be useful 
for COW and page_mkclean.

So

#define MMU_ATOMIC 1
#define MMU_WRITABLE 2

insted of the atomic parameter?

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