[RFC PATCH 23/26] userfaultfd: add UFFD_FEATURE_MINOR_HUGETLBFS_HGM

[James Houghton <jthoughton@google.com>]

This is so that userspace is aware that their kernel was compiled with
HugeTLB high-granularity mapping and that UFFDIO_CONTINUE down to
PAGE_SIZE-aligned chunks are valid.

Signed-off-by: James Houghton <jthoughton@google.com>
---
 fs/userfaultfd.c                 | 7 ++++++-
 include/uapi/linux/userfaultfd.h | 2 ++
 2 files changed, 8 insertions(+), 1 deletion(-)

diff --git a/fs/userfaultfd.c b/fs/userfaultfd.c
index 77c1b8a7d0b9..59bfdb7a67e0 100644
--- a/fs/userfaultfd.c
+++ b/fs/userfaultfd.c
@@ -1935,10 +1935,15 @@ static int userfaultfd_api(struct userfaultfd_ctx *ctx,
 		goto err_out;
 	/* 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 | UFFD_FEATURE_MINOR_SHMEM);
-#endif
+#ifndef CONFIG_HUGETLB_HIGH_GRANULARITY_MAPPING
+	uffdio_api.features &= ~UFFD_FEATURE_MINOR_HUGETLBFS_HGM;
+#endif  /* CONFIG_HUGETLB_HIGH_GRANULARITY_MAPPING */
+#endif  /* CONFIG_HAVE_ARCH_USERFAULTFD_MINOR */
+
 #ifndef CONFIG_HAVE_ARCH_USERFAULTFD_WP
 	uffdio_api.features &= ~UFFD_FEATURE_PAGEFAULT_FLAG_WP;
 #endif
diff --git a/include/uapi/linux/userfaultfd.h b/include/uapi/linux/userfaultfd.h
index 7d32b1e797fb..50fbcb0bcba0 100644
--- a/include/uapi/linux/userfaultfd.h
+++ b/include/uapi/linux/userfaultfd.h
@@ -32,6 +32,7 @@
 			   UFFD_FEATURE_SIGBUS |		\
 			   UFFD_FEATURE_THREAD_ID |		\
 			   UFFD_FEATURE_MINOR_HUGETLBFS |	\
+			   UFFD_FEATURE_MINOR_HUGETLBFS_HGM |	\
 			   UFFD_FEATURE_MINOR_SHMEM |		\
 			   UFFD_FEATURE_EXACT_ADDRESS |		\
 			   UFFD_FEATURE_WP_HUGETLBFS_SHMEM)
@@ -213,6 +214,7 @@ struct uffdio_api {
 #define UFFD_FEATURE_MINOR_SHMEM		(1<<10)
 #define UFFD_FEATURE_EXACT_ADDRESS		(1<<11)
 #define UFFD_FEATURE_WP_HUGETLBFS_SHMEM		(1<<12)
+#define UFFD_FEATURE_MINOR_HUGETLBFS_HGM	(1<<13)
 	__u64 features;
 
 	__u64 ioctls;
-- 
2.37.0.rc0.161.g10f37bed90-goog