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Date: Wed, 27 May 2015 10:32:00 -0400
From: Jerome Glisse <j.glisse@gmail.com>
To: "Aneesh Kumar K.V" <aneesh.kumar@linux.vnet.ibm.com>
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        =?iso-8859-1?B?Suly9G1l?= Glisse <jglisse@redhat.com>
Subject: Re: [PATCH 02/36] mmu_notifier: keep track of active invalidation
 ranges v3
Message-ID: <20150527143159.GA1948@gmail.com>
References: <1432236705-4209-1-git-send-email-j.glisse@gmail.com>
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On Wed, May 27, 2015 at 10:39:23AM +0530, Aneesh Kumar K.V wrote:
> j.glisse@gmail.com writes:
> 
> > From: Jérôme Glisse <jglisse@redhat.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