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.

[akpm@linux-foundation.org: improve the CONFIG_MMU=n situation, per SeongJae]
[vivek.kasireddy@intel.com: 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/20240624063952.1572359-4-vivek.kasireddy@intel.com
Signed-off-by: Vivek Kasireddy <vivek.kasireddy@intel.com>
Suggested-by: Jason Gunthorpe <jgg@nvidia.com>
Reviewed-by: Jason Gunthorpe <jgg@nvidia.com> (v2)
Reviewed-by: David Hildenbrand <david@redhat.com> (v3)
Reviewed-by: Christoph Hellwig <hch@lst.de> (v6)
Acked-by: Dave Airlie <airlied@redhat.com>
Acked-by: Gerd Hoffmann <kraxel@redhat.com>
Cc: Matthew Wilcox (Oracle) <willy@infradead.org>
Cc: Daniel Vetter <daniel.vetter@ffwll.ch>
Cc: Hugh Dickins <hughd@google.com>
Cc: Peter Xu <peterx@redhat.com>
Cc: Dongwon Kim <dongwon.kim@intel.com>
Cc: Junxiao Chang <junxiao.chang@intel.com>
Cc: Arnd Bergmann <arnd@arndb.de>
Cc: Christoph Hellwig <hch@infradead.org>
Cc: Mike Kravetz <mike.kravetz@oracle.com>
Cc: Oscar Salvador <osalvador@suse.de>
Cc: Shuah Khan <shuah@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

1 files changed, 45 insertions, 0 deletions

diff --git a/mm/memfd.c b/mm/memfd.c
index 7d8d3ab3fa37..e7b7c5294d59 100644
--- a/mm/memfd.c
+++ b/mm/memfd.c
@@ -60,6 +60,51 @@ static void memfd_tag_pins(struct xa_state *xas)
 }
 
 /*
+ * This is a helper function used by memfd_pin_user_pages() in GUP (gup.c).
+ * It is mainly called to allocate a folio in a memfd when the caller
+ * (memfd_pin_folios()) cannot find a folio in the page cache at a given
+ * index in the mapping.
+ */
+struct folio *memfd_alloc_folio(struct file *memfd, pgoff_t idx)
+{
+#ifdef CONFIG_HUGETLB_PAGE
+	struct folio *folio;
+	gfp_t gfp_mask;
+	int err;
+
+	if (is_file_hugepages(memfd)) {
+		/*
+		 * The folio would most likely be accessed by a DMA driver,
+		 * therefore, we have zone memory constraints where we can
+		 * alloc from. Also, the folio will be pinned for an indefinite
+		 * amount of time, so it is not expected to be migrated away.
+		 */
+		gfp_mask = htlb_alloc_mask(hstate_file(memfd));
+		gfp_mask &= ~(__GFP_HIGHMEM | __GFP_MOVABLE);
+
+		folio = alloc_hugetlb_folio_nodemask(hstate_file(memfd),
+						     numa_node_id(),
+						     NULL,
+						     gfp_mask,
+						     false);
+		if (folio && folio_try_get(folio)) {
+			err = hugetlb_add_to_page_cache(folio,
+							memfd->f_mapping,
+							idx);
+			if (err) {
+				folio_put(folio);
+				free_huge_folio(folio);
+				return ERR_PTR(err);
+			}
+			return folio;
+		}
+		return ERR_PTR(-ENOMEM);
+	}
+#endif
+	return shmem_read_folio(memfd->f_mapping, idx);
+}
+
+/*
  * Setting SEAL_WRITE requires us to verify there's no pending writer. However,
  * via get_user_pages(), drivers might have some pending I/O without any active
  * user-space mappings (eg., direct-IO, AIO). Therefore, we look at all folios