[RFC PATCH v2 33/47] userfaultfd: add UFFD_FEATURE_MINOR_HUGETLBFS_HGM

[James Houghton]

Userspace must provide this new feature when it calls UFFDIO_API to
enable HGM. Userspace can check if the feature exists in
uffdio_api.features, and if it does not exist, the kernel does not
support and therefore did not enable HGM.

Signed-off-by: James Houghton <jthoughton@xxxxxxxxxx>
---
 fs/userfaultfd.c                 | 12 +++++++++++-
 include/linux/userfaultfd_k.h    |  7 +++++++
 include/uapi/linux/userfaultfd.h |  2 ++
 3 files changed, 20 insertions(+), 1 deletion(-)

diff --git a/fs/userfaultfd.c b/fs/userfaultfd.c
index 07c81ab3fd4d..3a3e9ef74dab 100644
--- a/fs/userfaultfd.c
+++ b/fs/userfaultfd.c
@@ -226,6 +226,11 @@ static inline struct uffd_msg userfault_msg(unsigned long address,
 	return msg;
 }
 
+bool uffd_ctx_has_hgm(struct vm_userfaultfd_ctx *ctx)
+{
+	return ctx->ctx->features & UFFD_FEATURE_MINOR_HUGETLBFS_HGM;
+}
+
 #ifdef CONFIG_HUGETLB_PAGE
 /*
  * Same functionality as userfaultfd_must_wait below with modifications for
@@ -1954,10 +1959,15 @@ 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/linux/userfaultfd_k.h b/include/linux/userfaultfd_k.h
index f07e6998bb68..d8fa37f308f7 100644
--- a/include/linux/userfaultfd_k.h
+++ b/include/linux/userfaultfd_k.h
@@ -162,6 +162,8 @@ static inline bool vma_can_userfault(struct vm_area_struct *vma,
 	    vma_is_shmem(vma);
 }
 
+extern bool uffd_ctx_has_hgm(struct vm_userfaultfd_ctx *);
+
 extern int dup_userfaultfd(struct vm_area_struct *, struct list_head *);
 extern void dup_userfaultfd_complete(struct list_head *);
 
@@ -228,6 +230,11 @@ static inline bool userfaultfd_armed(struct vm_area_struct *vma)
 	return false;
 }
 
+static inline bool uffd_ctx_has_hgm(struct vm_userfaultfd_ctx *ctx)
+{
+	return false;
+}
+
 static inline int dup_userfaultfd(struct vm_area_struct *vma,
 				  struct list_head *l)
 {
diff --git a/include/uapi/linux/userfaultfd.h b/include/uapi/linux/userfaultfd.h
index 005e5e306266..ae8080003560 100644
--- a/include/uapi/linux/userfaultfd.h
+++ b/include/uapi/linux/userfaultfd.h
@@ -36,6 +36,7 @@
 			   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)
@@ -217,6 +218,7 @@ 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;
-- 
2.38.0.135.g90850a2211-goog