linux-kernel - Re: [PATCH 02/36] mmu_notifier: keep track of active invalidation ranges v3

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Date:	Wed, 27 May 2015 10:32:00 -0400
From:	Jerome Glisse <j.glisse@...il.com>
To:	"Aneesh Kumar K.V" <aneesh.kumar@...ux.vnet.ibm.com>
Cc:	akpm@...ux-foundation.org, linux-kernel@...r.kernel.org,
	linux-mm@...ck.org, Linus Torvalds <torvalds@...ux-foundation.org>,
	joro@...tes.org, Mel Gorman <mgorman@...e.de>,
	"H. Peter Anvin" <hpa@...or.com>,
	Peter Zijlstra <peterz@...radead.org>,
	Andrea Arcangeli <aarcange@...hat.com>,
	Johannes Weiner <jweiner@...hat.com>,
	Larry Woodman <lwoodman@...hat.com>,
	Rik van Riel <riel@...hat.com>,
	Dave Airlie <airlied@...hat.com>,
	Brendan Conoboy <blc@...hat.com>,
	Joe Donohue <jdonohue@...hat.com>,
	Duncan Poole <dpoole@...dia.com>,
	Sherry Cheung <SCheung@...dia.com>,
	Subhash Gutti <sgutti@...dia.com>,
	John Hubbard <jhubbard@...dia.com>,
	Mark Hairgrove <mhairgrove@...dia.com>,
	Lucien Dunning <ldunning@...dia.com>,
	Cameron Buschardt <cabuschardt@...dia.com>,
	Arvind Gopalakrishnan <arvindg@...dia.com>,
	Haggai Eran <haggaie@...lanox.com>,
	Shachar Raindel <raindel@...lanox.com>,
	Liran Liss <liranl@...lanox.com>,
	Roland Dreier <roland@...estorage.com>,
	Ben Sander <ben.sander@....com>,
	Greg Stoner <Greg.Stoner@....com>,
	John Bridgman <John.Bridgman@....com>,
	Michael Mantor <Michael.Mantor@....com>,
	Paul Blinzer <Paul.Blinzer@....com>,
	Laurent Morichetti <Laurent.Morichetti@....com>,
	Alexander Deucher <Alexander.Deucher@....com>,
	Oded Gabbay <Oded.Gabbay@....com>,
	Jérôme Glisse <jglisse@...hat.com>
Subject: Re: [PATCH 02/36] mmu_notifier: keep track of active invalidation
 ranges v3

On Wed, May 27, 2015 at 10:39:23AM +0530, Aneesh Kumar K.V wrote:
> j.glisse@...il.com writes:
> 
> > From: Jérôme Glisse <jglisse@...hat.com>
> >
> > The mmu_notifier_invalidate_range_start() and mmu_notifier_invalidate_range_end()
> > can be considered as forming an "atomic" section for the cpu page table update
> > point of view. Between this two function the cpu page table content is unreliable
> > for the address range being invalidated.
> >
> > Current user such as kvm need to know when they can trust the content of the cpu
> > page table. This becomes even more important to new users of the mmu_notifier
> > api (such as HMM or ODP).
> 
> I don't see kvm using the new APIs in this patch. Also what is that HMM use this
> for, to protect walking of mirror page table ?. I am sure you are
> covering that in the later patches. May be you may want to mention
> the details here too. 

KVM side is not done, i looked at KVM code long time ago and thought oh it
could take advantage of this but now i do not remember exactly. I would need
to check back.

For HMM this is simple, no device fault can populate or walk the mirror page
table on a range that is being invalidated. But concurrent fault/walk can
happen outside the invalidated range. All handled in hmm_device_fault_start().

Cheers,
Jérôme
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