The new routines are:
    iov_iter_pin_user_pages()
    iov_iter_pin_user_pages_alloc()

and those correspond to these pre-existing routines:
    iov_iter_get_pages()
    iov_iter_get_pages_alloc()

Also, pipe_get_pages() and related are changed so as to pass
down a "use_pup" (use pin_user_page() instead of get_page()) bool
argument.

Unlike the iov_iter_get_pages*() routines, the
iov_iter_pin_user_pages*() routines assert that only ITER_IOVEC or
ITER_PIPE items are passed in. They then call pin_user_page*(), instead
of get_user_pages_fast() or get_page().

Why: In order to incrementally change Direct IO callers from calling
get_user_pages_fast() and put_page(), over to calling
pin_user_pages_fast() and unpin_user_page(), there need to be mid-level
routines that specifically call one or the other systems, for both page
acquisition and page release.

Signed-off-by: John Hubbard <jhubbard@nvidia.com>
---
 include/linux/uio.h |   5 ++
 lib/iov_iter.c      | 110 ++++++++++++++++++++++++++++++++++++++++----
 2 files changed, 107 insertions(+), 8 deletions(-)

diff --git a/include/linux/uio.h b/include/linux/uio.h
index 3835a8a8e9ea..29b0504a27cc 100644
--- a/include/linux/uio.h
+++ b/include/linux/uio.h

@@ -229,6 +229,11 @@ int iov_iter_npages(const struct iov_iter *i, int maxpages);
 
 const void *dup_iter(struct iov_iter *new, struct iov_iter *old, gfp_t flags);
 
+ssize_t iov_iter_pin_user_pages(struct iov_iter *i, struct page **pages,
+			size_t maxsize, unsigned int maxpages, size_t *start);
+ssize_t iov_iter_pin_user_pages_alloc(struct iov_iter *i, struct page ***pages,
+			size_t maxsize, size_t *start);
+
 static inline size_t iov_iter_count(const struct iov_iter *i)
 {
 	return i->count;

diff --git a/lib/iov_iter.c b/lib/iov_iter.c
index 5e40786c8f12..f25555eb3279 100644
--- a/lib/iov_iter.c
+++ b/lib/iov_iter.c

@@ -1269,7 +1269,8 @@ static inline ssize_t __pipe_get_pages(struct iov_iter *i,
 				size_t maxsize,
 				struct page **pages,
 				int iter_head,
-				size_t *start)
+				size_t *start,
+				bool use_pup)
 {
 	struct pipe_inode_info *pipe = i->pipe;
 	unsigned int p_mask = pipe->ring_size - 1;

@@ -1280,7 +1281,11 @@ static inline ssize_t __pipe_get_pages(struct iov_iter *i,
 	maxsize = n;
 	n += *start;
 	while (n > 0) {
-		get_page(*pages++ = pipe->bufs[iter_head & p_mask].page);
+		if (use_pup)
+			pin_user_page(*pages++ = pipe->bufs[iter_head & p_mask].page);
+		else
+			get_page(*pages++ = pipe->bufs[iter_head & p_mask].page);