Re: [PATCH 08 of 11] anon-vma-rwsem

From: Nick Piggin <npiggin@suse.de>
To: Christoph Lameter <clameter@sgi.com>
Cc: Robin Holt <holt@sgi.com>, Nick Piggin <nickpiggin@yahoo.com.au>,
	Linus Torvalds <torvalds@linux-foundation.org>,
	Andrea Arcangeli <andrea@qumranet.com>,
	Andrew Morton <akpm@linux-foundation.org>,
	Jack Steiner <steiner@sgi.com>,
	Peter Zijlstra <a.p.zijlstra@chello.nl>,
	kvm-devel@lists.sourceforge.net,
	Kanoj Sarcar <kanojsarcar@yahoo.com>,
	Roland Dreier <rdreier@cisco.com>,
	Steve Wise <swise@opengridcomputing.com>,
	linux-kernel@vger.kernel.org, Avi Kivity <avi@qumranet.com>,
	linux-mm@kvack.org, general@lists.openfabrics.org,
	Hugh Dickins <hugh@veritas.com>,
	Rusty Russell <rusty@rustcorp.com.au>,
	Anthony Liguori <aliguori@us.ibm.com>,
	Chris Wright <chrisw@redhat.com>,
	Marcelo Tosatti <marcelo@kvack.org>,
	Eric Dumazet <dada1@cosmosbay.com>,
	"Paul E. McKenney" <paulmck@us.ibm.com>
Subject: Re: [PATCH 08 of 11] anon-vma-rwsem
Date: Fri, 16 May 2008 01:52:03 +0200	[thread overview]
Message-ID: <20080515235203.GB25305@wotan.suse.de> (raw)
In-Reply-To: <Pine.LNX.4.64.0805151031250.18708@schroedinger.engr.sgi.com>

On Thu, May 15, 2008 at 10:33:57AM -0700, Christoph Lameter wrote:
> On Thu, 15 May 2008, Nick Piggin wrote:
> 
> > Oh, I get that confused because of the mixed up naming conventions
> > there: unmap_page_range should actually be called zap_page_range. But
> > at any rate, yes we can easily zap pagetables without holding mmap_sem.
> 
> How is that synchronized with code that walks the same pagetable. These 
> walks may not hold mmap_sem either. I would expect that one could only 
> remove a portion of the pagetable where we have some sort of guarantee 
> that no accesses occur. So the removal of the vma prior ensures that?

I don't really understand the question. If you remove the pte and invalidate
the TLBS on the remote image's process (importing the page), then it can
of course try to refault the page in because it's vma is still there. But
you catch that refault in your driver , which can prevent the page from
being faulted back in.