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Date:   Thu, 16 Jan 2020 10:13:11 -0400
From:   Jason Gunthorpe <jgg@ziepe.ca>
To:     Ralph Campbell <rcampbell@nvidia.com>
Cc:     "linux-rdma@vger.kernel.org" <linux-rdma@vger.kernel.org>,
        "linux-mm@kvack.org" <linux-mm@kvack.org>,
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        Jerome Glisse <jglisse@redhat.com>,
        John Hubbard <jhubbard@nvidia.com>,
        Christoph Hellwig <hch@lst.de>,
        Andrew Morton <akpm@linux-foundation.org>,
        Shuah Khan <shuah@kernel.org>
Subject: Re: [PATCH v5 1/2] mm/mmu_notifier: make interval notifier updates
 safe
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On Wed, Jan 15, 2020 at 02:04:47PM -0800, Ralph Campbell wrote:

> But I see your point if this sequence is done outside of the invalidate
> callback. In that case, if the driver shrank the interval, an invalidate
> callback for the right hand side could be missed before the insertion of
> the new interval for the right hand side.
> I'll explain this in the comments for nouveau_svmm_do_unmap() and
> dmirror_do_unmap().

Yes, this is why I'm not sure this is a good API for the core to
expose.

Batch manipulations is a resonable thing, but it should be forced to
work under safe conditions, ie while holding the required 'inv_begin'
on the interval tree, and the batching APIs should assert this
requirement.

Jason