userfaultfd/shmem: advertise shmem minor fault support

Now that the feature is fully implemented (the faulting path hooks exist
so userspace is notified, and the ioctl to resolve such faults is
available), advertise this as a supported feature.

Link: https://lkml.kernel.org/r/20210503180737.2487560-6-axelrasmussen@google.com
Signed-off-by: Axel Rasmussen <axelrasmussen@google.com>
Acked-by: Hugh Dickins <hughd@google.com>
Acked-by: Peter Xu <peterx@redhat.com>
Cc: Alexander Viro <viro@zeniv.linux.org.uk>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: Brian Geffon <bgeffon@google.com>
Cc: "Dr . David Alan Gilbert" <dgilbert@redhat.com>
Cc: Jerome Glisse <jglisse@redhat.com>
Cc: Joe Perches <joe@perches.com>
Cc: Kirill A. Shutemov <kirill@shutemov.name>
Cc: Lokesh Gidra <lokeshgidra@google.com>
Cc: Mike Kravetz <mike.kravetz@oracle.com>
Cc: Mike Rapoport <rppt@linux.vnet.ibm.com>
Cc: Mina Almasry <almasrymina@google.com>
Cc: Oliver Upton <oupton@google.com>
Cc: Shaohua Li <shli@fb.com>
Cc: Shuah Khan <shuah@kernel.org>
Cc: Stephen Rothwell <sfr@canb.auug.org.au>
Cc: Wang Qing <wangqing@vivo.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

diff --git a/Documentation/admin-guide/mm/userfaultfd.rst b/Documentation/admin-guide/mm/userfaultfd.rst
index 3aa38e8b8361d821e26400a0d1c80c6a1174f61d..6528036093e1fb5a56cf3a7a8fdf0c43fa7e6fe2 100644 (file)
--- a/Documentation/admin-guide/mm/userfaultfd.rst
+++ b/Documentation/admin-guide/mm/userfaultfd.rst
@@ -77,7 +77,8 @@ events, except page fault notifications, may be generated:
 
 - ``UFFD_FEATURE_MINOR_HUGETLBFS`` indicates that the kernel supports
   ``UFFDIO_REGISTER_MODE_MINOR`` registration for hugetlbfs virtual memory
-  areas.
+  areas. ``UFFD_FEATURE_MINOR_SHMEM`` is the analogous feature indicating
+  support for shmem virtual memory areas.
 
 The userland application should set the feature flags it intends to use
 when invoking the ``UFFDIO_API`` ioctl, to request that those features be

diff --git a/fs/userfaultfd.c b/fs/userfaultfd.c
index 82ef253d66b68356e3dd2ec27bac21ef56fc1420..19ebae443ade96cf454bb4b5e79f36beeb47b295 100644 (file)
--- a/fs/userfaultfd.c
+++ b/fs/userfaultfd.c
@@ -1944,7 +1944,8 @@ static int userfaultfd_api(struct userfaultfd_ctx *ctx,
        /* report all available features and ioctls to userland */
        uffdio_api.features = UFFD_API_FEATURES;
 #ifndef CONFIG_HAVE_ARCH_USERFAULTFD_MINOR
-       uffdio_api.features &= ~UFFD_FEATURE_MINOR_HUGETLBFS;
+       uffdio_api.features &=
+               ~(UFFD_FEATURE_MINOR_HUGETLBFS | UFFD_FEATURE_MINOR_SHMEM);
 #endif
 #ifndef CONFIG_HAVE_ARCH_USERFAULTFD_WP
        uffdio_api.features &= ~UFFD_FEATURE_PAGEFAULT_FLAG_WP;

diff --git a/include/uapi/linux/userfaultfd.h b/include/uapi/linux/userfaultfd.h
index 650480f41f1d5f9f2776c2d5e000ecc89453cba7..05b31d60acf654bb5c38d149c6823b8712c5c893 100644 (file)
--- a/include/uapi/linux/userfaultfd.h
+++ b/include/uapi/linux/userfaultfd.h
@@ -31,7 +31,8 @@
                           UFFD_FEATURE_MISSING_SHMEM |         \
                           UFFD_FEATURE_SIGBUS |                \
                           UFFD_FEATURE_THREAD_ID |             \
-                          UFFD_FEATURE_MINOR_HUGETLBFS)
+                          UFFD_FEATURE_MINOR_HUGETLBFS |       \
+                          UFFD_FEATURE_MINOR_SHMEM)
 #define UFFD_API_IOCTLS                                \
        ((__u64)1 << _UFFDIO_REGISTER |         \
         (__u64)1 << _UFFDIO_UNREGISTER |       \
@@ -185,6 +186,9 @@ struct uffdio_api {
         * UFFD_FEATURE_MINOR_HUGETLBFS indicates that minor faults
         * can be intercepted (via REGISTER_MODE_MINOR) for
         * hugetlbfs-backed pages.
+        *
+        * UFFD_FEATURE_MINOR_SHMEM indicates the same support as
+        * UFFD_FEATURE_MINOR_HUGETLBFS, but for shmem-backed pages instead.
         */
 #define UFFD_FEATURE_PAGEFAULT_FLAG_WP         (1<<0)
 #define UFFD_FEATURE_EVENT_FORK                        (1<<1)
@@ -196,6 +200,7 @@ struct uffdio_api {
 #define UFFD_FEATURE_SIGBUS                    (1<<7)
 #define UFFD_FEATURE_THREAD_ID                 (1<<8)
 #define UFFD_FEATURE_MINOR_HUGETLBFS           (1<<9)
+#define UFFD_FEATURE_MINOR_SHMEM               (1<<10)
        __u64 features;
 
        __u64 ioctls;