From: John Hubbard <jhubbard@nvidia.com>

This patch sets and restores the new page->dma_pinned_flags and
page->dma_pinned_count fields, but does not actually use them for
anything yet.

In order to use these fields at all, the page must be removed from
any LRU list that it's on. The patch also adds some precautions that
prevent the page from getting moved back onto an LRU, once it is
in this state.

This is in preparation to fix some problems that came up when using
devices (NICs, GPUs, for example) that set up direct access to a chunk
of system (CPU) memory, so that they can DMA to/from that memory.

Cc: Matthew Wilcox <willy@infradead.org>
Cc: Michal Hocko <mhocko@kernel.org>
Cc: Christopher Lameter <redacted>
Cc: Jason Gunthorpe <jgg@ziepe.ca>
Cc: Dan Williams <redacted>
Cc: Jan Kara <jack@suse.cz>
Signed-off-by: John Hubbard <jhubbard@nvidia.com>
---
 include/linux/mm.h | 19 +++++----------
 mm/gup.c           | 55 +++++++++++++++++++++++++++++++++++++++++--
 mm/memcontrol.c    |  8 +++++++
 mm/swap.c          | 58 ++++++++++++++++++++++++++++++++++++++++++++++
 4 files changed, 125 insertions(+), 15 deletions(-)

diff --git a/include/linux/mm.h b/include/linux/mm.h
index 09fbb2c81aba..6c64b1e0b777 100644
--- a/include/linux/mm.h
+++ b/include/linux/mm.h

@@ -950,6 +950,10 @@ static inline void put_page(struct page *page)
 {
 	page = compound_head(page);
 
+	VM_BUG_ON_PAGE(PageDmaPinned(page) &&
+		       page_ref_count(page) <
+				atomic_read(&page->dma_pinned_count),
+		       page);
 	/*
 	 * For devmap managed pages we need to catch refcount transition from
 	 * 2 to 1, when refcount reach one it means the page is free and we

@@ -964,21 +968,10 @@ static inline void put_page(struct page *page)
 }
 
 /*
- * put_user_page() - release a page that had previously been acquired via
- * a call to one of the get_user_pages*() functions.
- *
  * Pages that were pinned via get_user_pages*() must be released via
- * either put_user_page(), or one of the put_user_pages*() routines
- * below. This is so that eventually, pages that are pinned via
- * get_user_pages*() can be separately tracked and uniquely handled. In
- * particular, interactions with RDMA and filesystems need special
- * handling.
+ * one of these put_user_pages*() routines:
  */
-static inline void put_user_page(struct page *page)
-{
-	put_page(page);
-}
-
+void put_user_page(struct page *page);
 void put_user_pages_dirty(struct page **pages, unsigned long npages);
 void put_user_pages_dirty_lock(struct page **pages, unsigned long npages);
 void put_user_pages(struct page **pages, unsigned long npages);

diff --git a/mm/gup.c b/mm/gup.c
index 55a41dee0340..ec1b26591532 100644
--- a/mm/gup.c
+++ b/mm/gup.c

@@ -25,6 +25,50 @@ struct follow_page_context {
 	unsigned int page_mask;
 };
 
+static void pin_page_for_dma(struct page *page)
+{
+	int ret = 0;
+	struct zone *zone;
+
+	page = compound_head(page);
+	zone = page_zone(page);
+
+	spin_lock(zone_gup_lock(zone));