linux-kernel - Re: [PATCH v6 5/6] nouveau: use new mmu interval notifiers

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Date:   Thu, 16 Jan 2020 20:21:55 +0000
From:   Jason Gunthorpe <jgg@...lanox.com>
To:     Ralph Campbell <rcampbell@...dia.com>
CC:     "linux-rdma@...r.kernel.org" <linux-rdma@...r.kernel.org>,
        "linux-mm@...ck.org" <linux-mm@...ck.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "nouveau@...ts.freedesktop.org" <nouveau@...ts.freedesktop.org>,
        "linux-kselftest@...r.kernel.org" <linux-kselftest@...r.kernel.org>,
        Jerome Glisse <jglisse@...hat.com>,
        John Hubbard <jhubbard@...dia.com>,
        Christoph Hellwig <hch@....de>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Ben Skeggs <bskeggs@...hat.com>, Shuah Khan <shuah@...nel.org>
Subject: Re: [PATCH v6 5/6] nouveau: use new mmu interval notifiers

On Thu, Jan 16, 2020 at 12:16:30PM -0800, Ralph Campbell wrote:
> Can you point me to the latest ODP code? Seems like my understanding is
> quite off.

https://elixir.bootlin.com/linux/v5.5-rc6/source/drivers/infiniband/hw/mlx5/odp.c

Look for the word 'implicit'

mlx5_ib_invalidate_range() releases the interval_notifier when there are
no populated shadow PTEs in its leaf

pagefault_implicit_mr() creates an interval_notifier that covers the
level in the page table that needs population. Notice it just uses an
unlocked xa_load to find the page table level.

The locking is pretty tricky as it relies on RCU, but the fault flow
is fairly lightweight.

Jason