mm/gup: introduce memfd_pin_folios() for pinning memfd folios

For drivers that would like to longterm-pin the folios associated with a
memfd, the memfd_pin_folios() API provides an option to not only pin the
folios via FOLL_PIN but also to check and migrate them if they reside in
movable zone or CMA block.  This API currently works with memfds but it
should work with any files that belong to either shmemfs or hugetlbfs. 
Files belonging to other filesystems are rejected for now.

The folios need to be located first before pinning them via FOLL_PIN.  If
they are found in the page cache, they can be immediately pinned. 
Otherwise, they need to be allocated using the filesystem specific APIs
and then pinned.

[[email protected]: improve the CONFIG_MMU=n situation, per SeongJae]
[[email protected]: return -EINVAL if the end offset is greater than the size of memfd]
  Link: https://lkml.kernel.org/r/IA0PR11MB71850525CBC7D541CAB45DF1F8DB2@IA0PR11MB7185.namprd11.prod.outlook.com
Link: https://lkml.kernel.org/r/[email protected]
Signed-off-by: Vivek Kasireddy <[email protected]>
Suggested-by: Jason Gunthorpe <[email protected]>
Reviewed-by: Jason Gunthorpe <[email protected]> (v2)
Reviewed-by: David Hildenbrand <[email protected]> (v3)
Reviewed-by: Christoph Hellwig <[email protected]> (v6)
Acked-by: Dave Airlie <[email protected]>
Acked-by: Gerd Hoffmann <[email protected]>
Cc: Matthew Wilcox (Oracle) <[email protected]>
Cc: Daniel Vetter <[email protected]>
Cc: Hugh Dickins <[email protected]>
Cc: Peter Xu <[email protected]>
Cc: Dongwon Kim <[email protected]>
Cc: Junxiao Chang <[email protected]>
Cc: Arnd Bergmann <[email protected]>
Cc: Christoph Hellwig <[email protected]>
Cc: Mike Kravetz <[email protected]>
Cc: Oscar Salvador <[email protected]>
Cc: Shuah Khan <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>

2 files changed, 8 insertions, 0 deletions

diff --git a/include/linux/memfd.h b/include/linux/memfd.h
index e7abf6fa4c52..3f2cf339ceaf 100644
--- a/include/linux/memfd.h
+++ b/include/linux/memfd.h
@@ -6,11 +6,16 @@
 
 #ifdef CONFIG_MEMFD_CREATE
 extern long memfd_fcntl(struct file *file, unsigned int cmd, unsigned int arg);
+struct folio *memfd_alloc_folio(struct file *memfd, pgoff_t idx);
 #else
 static inline long memfd_fcntl(struct file *f, unsigned int c, unsigned int a)
 {
 	return -EINVAL;
 }
+static inline struct folio *memfd_alloc_folio(struct file *memfd, pgoff_t idx)
+{
+	return ERR_PTR(-EINVAL);
+}
 #endif
 
 #endif /* __LINUX_MEMFD_H */
diff --git a/include/linux/mm.h b/include/linux/mm.h
index 7b84379e3a1b..5f1075d19600 100644
--- a/include/linux/mm.h
+++ b/include/linux/mm.h
@@ -2500,6 +2500,9 @@ long get_user_pages_unlocked(unsigned long start, unsigned long nr_pages,
 		    struct page **pages, unsigned int gup_flags);
 long pin_user_pages_unlocked(unsigned long start, unsigned long nr_pages,
 		    struct page **pages, unsigned int gup_flags);
+long memfd_pin_folios(struct file *memfd, loff_t start, loff_t end,
+		      struct folio **folios, unsigned int max_folios,
+		      pgoff_t *offset);
 
 int get_user_pages_fast(unsigned long start, int nr_pages,
 			unsigned int gup_flags, struct page **pages);