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

From: "Aneesh Kumar K.V" <aneesh.kumar@linux.vnet.ibm.com>
To: j.glisse@gmail.com, akpm@linux-foundation.org
Cc: linux-kernel@vger.kernel.org, linux-mm@kvack.org,
	"Linus Torvalds" <torvalds@linux-foundation.org>,
	joro@8bytes.org, "Mel Gorman" <mgorman@suse.de>,
	"H. Peter Anvin" <hpa@zytor.com>,
	"Peter Zijlstra" <peterz@infradead.org>,
	"Andrea Arcangeli" <aarcange@redhat.com>,
	"Johannes Weiner" <jweiner@redhat.com>,
	"Larry Woodman" <lwoodman@redhat.com>,
	"Rik van Riel" <riel@redhat.com>,
	"Dave Airlie" <airlied@redhat.com>,
	"Brendan Conoboy" <blc@redhat.com>,
	"Joe Donohue" <jdonohue@redhat.com>,
	"Duncan Poole" <dpoole@nvidia.com>,
	"Sherry Cheung" <SCheung@nvidia.com>,
	"Subhash Gutti" <sgutti@nvidia.com>,
	"John Hubbard" <jhubbard@nvidia.com>,
	"Mark Hairgrove" <mhairgrove@nvidia.com>,
	"Lucien Dunning" <ldunning@nvidia.com>,
	"Cameron Buschardt" <cabuschardt@nvidia.com>,
	"Arvind Gopalakrishnan" <arvindg@nvidia.com>,
	"Haggai Eran" <haggaie@mellanox.com>,
	"Shachar Raindel" <raindel@mellanox.com>,
	"Liran Liss" <liranl@mellanox.com>,
	"Roland Dreier" <roland@purestorage.com>,
	"Ben Sander" <ben.sander@amd.com>,
	"Greg Stoner" <Greg.Stoner@amd.com>,
	"John Bridgman" <John.Bridgman@amd.com>,
	"Michael Mantor" <Michael.Mantor@amd.com>,
	"Paul Blinzer" <Paul.Blinzer@amd.com>,
	"Laurent Morichetti" <Laurent.Morichetti@amd.com>,
	"Alexander Deucher" <Alexander.Deucher@amd.com>,
	"Oded Gabbay" <Oded.Gabbay@amd.com>,
	"Jérôme Glisse" <jglisse@redhat.com>
Subject: Re: [PATCH 02/36] mmu_notifier: keep track of active invalidation ranges v3
Date: Wed, 27 May 2015 10:39:23 +0530	[thread overview]
Message-ID: <871ti2mwsc.fsf@linux.vnet.ibm.com> (raw)
In-Reply-To: <1432236705-4209-3-git-send-email-j.glisse@gmail.com>

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. 

>
> This patch use a structure define at all call site to invalidate_range_start()
> that is added to a list for the duration of the invalidation. It adds two new
> helpers to allow querying if a range is being invalidated or to wait for a range
> to become valid.
>
> For proper synchronization, user must block new range invalidation from inside
> there invalidate_range_start() callback, before calling the helper functions.
> Otherwise there is no garanty that a new range invalidation will not be added
> after the call to the helper function to query for existing range.
>
> Changed since v1:
>   - Fix a possible deadlock in mmu_notifier_range_wait_valid()
>
> Changed since v2:
>   - Add the range to invalid range list before calling ->range_start().
>   - Del the range from invalid range list after calling ->range_end().
>   - Remove useless list initialization.
>

-aneesh

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