Re: [RFC PATCH 3/5] mm/vma: add support for peer to peer to device vma

[Christoph Hellwig]

On Wed, Jan 30, 2019 at 01:50:27PM -0500, Jerome Glisse wrote:
> I do not see how VMA changes are any different than using struct page
> in respect to userspace exposure. Those vma callback do not need to be
> set by everyone, in fact expectation is that only handful of driver
> will set those.
> 
> How can we do p2p between RDMA and GPU for instance, without exposure
> to userspace ? At some point you need to tell userspace hey this kernel
> does allow you to do that :)

To do RDMA on a memory region you need struct page backÑng to start
with..