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

["Aneesh Kumar K.V" <aneesh.kumar@linux.vnet.ibm.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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