linux-kernel - Re: [kvm-devel] [patch 2/6] mmu_notifier: Callbacks to invalidate address ranges

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Date:	Wed, 30 Jan 2008 18:37:26 -0800 (PST)
From:	Christoph Lameter <clameter@....com>
To:	Robin Holt <holt@....com>
cc:	Andrea Arcangeli <andrea@...ranet.com>,
	Nick Piggin <npiggin@...e.de>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>, linux-mm@...ck.org,
	Benjamin Herrenschmidt <benh@...nel.crashing.org>,
	steiner@....com, linux-kernel@...r.kernel.org,
	Avi Kivity <avi@...ranet.com>, kvm-devel@...ts.sourceforge.net,
	daniel.blueman@...drics.com, Hugh Dickins <hugh@...itas.com>
Subject: Re: [kvm-devel] [patch 2/6] mmu_notifier: Callbacks to invalidate
 address ranges

On Wed, 30 Jan 2008, Robin Holt wrote:

> > Well the GRU uses follow_page() instead of get_user_pages. Performance is 
> > a major issue for the GRU. 
> 
> Worse, the GRU takes its TLB faults from within an interrupt so we
> use follow_page to prevent going to sleep.  That said, I think we
> could probably use follow_page() with FOLL_GET set to accomplish the
> requirements of mmu_notifier invalidate_range call.  Doesn't look too
> promising for hugetlb pages.

There may be no need to with the range_start/end scheme. The driver can 
have its own lock to make follow page secure. The lock needs to serialize 
the follow_page handler and the range_start/end calls as well as the 
invalidate_page callouts. I think that avoids the need for 
get_user_pages().


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