userfaultfd: hugetlbfs: UFFD_FEATURE_MISSING_SHMEM

Userland developers asked to be notified immediately by the UFFDIO_API
ioctl if shmem missing mode is supported by userfaultfd in the running
kernel.  This avoids the need to run UFFDIO_REGISTER on a shmem virtual
memory range to find out.

Link: http://lkml.kernel.org/r/20161216144821.5183-38-aarcange@redhat.com
Signed-off-by: Andrea Arcangeli <aarcange@redhat.com>
Cc: "Dr. David Alan Gilbert" <dgilbert@redhat.com>
Cc: Hillf Danton <hillf.zj@alibaba-inc.com>
Cc: Michael Rapoport <RAPOPORT@il.ibm.com>
Cc: Mike Kravetz <mike.kravetz@oracle.com>
Cc: Mike Rapoport <rppt@linux.vnet.ibm.com>
Cc: Pavel Emelyanov <xemul@parallels.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

diff --git a/include/uapi/linux/userfaultfd.h b/include/uapi/linux/userfaultfd.h
index 10631a4cdb24c0bac419aa8c6ce5833667f1a562..9ac4b68c54d18ed806534b1de726a1ea4b86ca7d 100644 (file)
--- a/include/uapi/linux/userfaultfd.h
+++ b/include/uapi/linux/userfaultfd.h
@@ -21,7 +21,8 @@
 #define UFFD_API_FEATURES (UFFD_FEATURE_EVENT_FORK |           \
                           UFFD_FEATURE_EVENT_REMAP |           \
                           UFFD_FEATURE_EVENT_MADVDONTNEED |    \
-                          UFFD_FEATURE_MISSING_HUGETLBFS)
+                          UFFD_FEATURE_MISSING_HUGETLBFS |     \
+                          UFFD_FEATURE_MISSING_SHMEM)
 #define UFFD_API_IOCTLS                                \
        ((__u64)1 << _UFFDIO_REGISTER |         \
         (__u64)1 << _UFFDIO_UNREGISTER |       \
@@ -146,12 +147,17 @@ struct uffdio_api {
         *    it, so userland can later check if the feature flag is
         *    present in uffdio_api.features after UFFDIO_API
         *    succeeded.
+        *
+        * UFFD_FEATURE_MISSING_SHMEM works the same as
+        * UFFD_FEATURE_MISSING_HUGETLBFS, but it applies to shmem
+        * (i.e. tmpfs and other shmem based APIs).
         */
 #define UFFD_FEATURE_PAGEFAULT_FLAG_WP         (1<<0)
 #define UFFD_FEATURE_EVENT_FORK                        (1<<1)
 #define UFFD_FEATURE_EVENT_REMAP               (1<<2)
 #define UFFD_FEATURE_EVENT_MADVDONTNEED                (1<<3)
 #define UFFD_FEATURE_MISSING_HUGETLBFS         (1<<4)
+#define UFFD_FEATURE_MISSING_SHMEM             (1<<5)
        __u64 features;
 
        __u64 ioctls;