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

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Message-ID: <Pine.LNX.4.64.0801291153520.25300@schroedinger.engr.sgi.com>
Date:	Tue, 29 Jan 2008 11:55:10 -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>, Nick Piggin <npiggin@...e.de>,
	kvm-devel@...ts.sourceforge.net,
	Benjamin Herrenschmidt <benh@...nel.crashing.org>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>, steiner@....com,
	linux-kernel@...r.kernel.org, linux-mm@...ck.org,
	daniel.blueman@...drics.com, Hugh Dickins <hugh@...itas.com>
Subject: Re: [patch 2/6] mmu_notifier: Callbacks to invalidate address ranges

On Tue, 29 Jan 2008, Andrea Arcangeli wrote:

> > +	mmu_notifier(invalidate_range, mm, address,
> > +				address + PAGE_SIZE - 1, 0);
> >  	page_table = pte_offset_map_lock(mm, pmd, address, &ptl);
> >  	if (likely(pte_same(*page_table, orig_pte))) {
> >  		if (old_page) {
> 
> What's the point of invalidate_range when the size is PAGE_SIZE? And
> how can it be right to invalidate_range _before_ ptep_clear_flush?

I am not sure. AFAICT you wrote that code.

It seems to be okay to invalidate range if you hold mmap_sem writably. In 
that case no additional faults can happen that would create new ptes.



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