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 10631a4..9ac4b68 100644
--- 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 @@
* 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;