MAP_DIRECT is an mmap(2) flag with the following semantics:

  MAP_DIRECT
  When specified with MAP_SHARED_VALIDATE, sets up a file lease with the
  same lifetime as the mapping. Unlike a typical F_RDLCK lease this lease
  is broken when a "lease breaker" attempts to write(2), change the block
  map (fallocate), or change the size of the file. Otherwise the mechanism
  of a lease break is identical to the typical lease break case where the
  lease needs to be removed (munmap) within the number of seconds
  specified by /proc/sys/fs/lease-break-time. If the lease holder fails to
  remove the lease in time the kernel will invalidate the mapping and
  force all future accesses to the mapping to trigger SIGBUS.

  In addition to lease break timeouts causing faults in the mapping to
  result in SIGBUS, other states of the file will trigger SIGBUS at fault
  time:

      * The file is not DAX capable
      * The file has reflinked (copy-on-write) blocks
      * The fault would trigger the filesystem to allocate blocks
      * The fault would trigger the filesystem to perform extent conversion

  In other words, MAP_DIRECT expects and enforces a fully allocated file
  where faults can be satisfied without modifying block map metadata.

  An unprivileged process may establish a MAP_DIRECT mapping on a file
  whose UID (owner) matches the filesystem UID of the  process. A process
  with the CAP_LEASE capability may establish a MAP_DIRECT mapping on
  arbitrary files

  ERRORS
  EACCES Beyond the typical mmap(2) conditions that trigger EACCES
  MAP_DIRECT also requires the permission to set a file lease.

  EOPNOTSUPP The filesystem explicitly does not support the flag

  SIGBUS Attempted to write a MAP_DIRECT mapping at a file offset that
         might require block-map updates, or the lease timed out and the
         kernel invalidated the mapping.

Cc: Jan Kara <jack@suse.cz>
Cc: Arnd Bergmann <arnd@arndb.de>
Cc: Jeff Moyer <redacted>
Cc: Christoph Hellwig <hch@lst.de>
Cc: Dave Chinner <david@fromorbit.com>
Cc: Alexander Viro <viro@zeniv.linux.org.uk>
Cc: "Darrick J. Wong" <redacted>
Cc: Ross Zwisler <redacted>
Cc: Jeff Layton <redacted>
Cc: "J. Bruce Fields" <redacted>
Signed-off-by: Dan Williams <redacted>
---
 fs/xfs/Kconfig                  |    2 -
 fs/xfs/xfs_file.c               |  102 +++++++++++++++++++++++++++++++++++++++
 include/linux/mman.h            |    3 +
 include/uapi/asm-generic/mman.h |    1 
 4 files changed, 106 insertions(+), 2 deletions(-)

diff --git a/fs/xfs/Kconfig b/fs/xfs/Kconfig
index f62fc6629abb..f8765653a438 100644
--- a/fs/xfs/Kconfig
+++ b/fs/xfs/Kconfig

@@ -112,4 +112,4 @@ config XFS_ASSERT_FATAL
 
 config XFS_LAYOUT
 	def_bool y
-	depends on EXPORTFS_BLOCK_OPS
+	depends on EXPORTFS_BLOCK_OPS || FS_DAX

diff --git a/fs/xfs/xfs_file.c b/fs/xfs/xfs_file.c
index ebdd0bd2b261..e35518600e28 100644
--- a/fs/xfs/xfs_file.c
+++ b/fs/xfs/xfs_file.c

@@ -40,12 +40,22 @@
 #include "xfs_iomap.h"
 #include "xfs_reflink.h"
 
+#include <linux/mman.h>
 #include <linux/dcache.h>
 #include <linux/falloc.h>
 #include <linux/pagevec.h>
+#include <linux/mapdirect.h>
 #include <linux/backing-dev.h>
 
 static const struct vm_operations_struct xfs_file_vm_ops;
+static const struct vm_operations_struct xfs_file_vm_direct_ops;
+
+static inline bool
+is_xfs_map_direct(
+		struct vm_area_struct *vma)
+{
+	return vma->vm_ops == &xfs_file_vm_direct_ops;
+}

 
 /*
  * Clear the specified ranges to zero through either the pagecache or DAX.

@@ -1008,6 +1018,26 @@ xfs_file_llseek(
 	return vfs_setpos(file, offset, inode->i_sb->s_maxbytes);
 }
 
+static int
+xfs_vma_checks(
+	struct vm_area_struct	*vma,
+	struct inode		*inode)

+
+	return 0;
+}
+
 /*
  * Locking for serialisation of IO during page faults. This results in a lock
  * ordering of:

@@ -1024,6 +1054,7 @@ __xfs_filemap_fault(
 	enum page_entry_size	pe_size,
 	bool			write_fault)
 {
+	struct vm_area_struct	*vma = vmf->vma;
 	struct inode		*inode = file_inode(vmf->vma->vm_file);