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

[Jason Gunthorpe]

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