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

From: Dan Williams <dan.j.williams@intel.com>
To: John Hubbard <jhubbard@nvidia.com>
Cc: Christoph Hellwig <hch@lst.de>, Jason Gunthorpe <jgg@ziepe.ca>,
	john.hubbard@gmail.com, Matthew Wilcox <willy@infradead.org>,
	Michal Hocko <mhocko@kernel.org>,
	Christopher Lameter <cl@linux.com>, Jan Kara <jack@suse.cz>,
	Linux MM <linux-mm@kvack.org>,
	LKML <linux-kernel@vger.kernel.org>,
	linux-rdma <linux-rdma@vger.kernel.org>
Subject: Re: [PATCH 2/2] mm: set PG_dma_pinned on get_user_pages*()
Date: Mon, 18 Jun 2018 10:56:57 -0700	[thread overview]
Message-ID: <CAPcyv4iacHYxGmyWokFrVsmxvLj7=phqp2i0tv8z6AT-mYuEEA@mail.gmail.com> (raw)
In-Reply-To: <d4817192-6db0-2f3f-7c67-6078b69686d3@nvidia.com>

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.