Re: [PATCH 2/2] mm: set PG_dma_pinned on get_user_pages*()

Dan Williams
2018-06-18T17:57:01Z

On Mon, Jun 18, 2018 at 10:50 AM, John Hubbard <jhubbard@nvidia.com> wrote:
> On 06/18/2018 01:12 AM, Christoph Hellwig wrote:
>> On Sun, Jun 17, 2018 at 01:28:18PM -0700, John Hubbard wrote:
>>> Yes. However, my thinking was: get_user_pages() can become a way to indicate that
>>> these pages are going to be treated specially. In particular, the caller
>>> does not really want or need to support certain file operations, while the
>>> page is flagged this way.
>>>
>>> If necessary, we could add a new API call.
>>
>> That API call is called get_user_pages_longterm.
>
> OK...I had the impression that this was just semi-temporary API for dax, but
> given that it's an exported symbol, I guess it really is here to stay.

The plan is to go back and provide api changes that bypass
get_user_page_longterm() for RDMA. However, for VFIO and others, it's
not clear what we could do. In the VFIO case the guest would need to
be prepared handle the revocation.