Re: [PATCH 2/3] mm/gup: Introduce get_user_pages_fast_longterm()

From: Ira Weiny <redacted>

Users of get_user_pages_fast are not protected against mapping
pages within FS DAX.  Introduce a call which protects them.

We do this by checking for DEVMAP pages during the fast walk and
falling back to the longterm gup call to check for FS DAX if needed.

Signed-off-by: Ira Weiny <redacted>
 include/linux/mm.h |   8 ++++
 mm/gup.c           | 102 +++++++++++++++++++++++++++++++++++----------
 2 files changed, 88 insertions(+), 22 deletions(-)

diff --git a/include/linux/mm.h b/include/linux/mm.h
index 80bb6408fe73..8f831c823630 100644
+++ b/include/linux/mm.h

@@ -1540,6 +1540,8 @@ long get_user_pages_unlocked(unsigned long start, unsigned long nr_pages,
 long get_user_pages_longterm(unsigned long start, unsigned long nr_pages,
 			    unsigned int gup_flags, struct page **pages,
 			    struct vm_area_struct **vmas);
+int get_user_pages_fast_longterm(unsigned long start, int nr_pages, bool write,
+				 struct page **pages);
 #else
 static inline long get_user_pages_longterm(unsigned long start,
 		unsigned long nr_pages, unsigned int gup_flags,

@@ -1547,6 +1549,11 @@ static inline long get_user_pages_longterm(unsigned long start,
 {
 	return get_user_pages(start, nr_pages, gup_flags, pages, vmas);
 }
+static inline int get_user_pages_fast_longterm(unsigned long start, int nr_pages,
+					       bool write, struct page **pages)
+{
+	return get_user_pages_fast(start, nr_pages, write, pages);
+}
 #endif /* CONFIG_FS_DAX */
 
 int get_user_pages_fast(unsigned long start, int nr_pages, int write,

@@ -2615,6 +2622,7 @@ struct page *follow_page(struct vm_area_struct *vma, unsigned long address,
 #define FOLL_REMOTE	0x2000	/* we are working on non-current tsk/mm */
 #define FOLL_COW	0x4000	/* internal GUP flag */
 #define FOLL_ANON	0x8000	/* don't do file mappings */
+#define FOLL_LONGTERM	0x10000	/* mapping is intended for a long term pin */