diff --git a/fs/userfaultfd.c b/fs/userfaultfd.c
index e5ce3b4..ba35caf 100644
--- a/fs/userfaultfd.c
+++ b/fs/userfaultfd.c
@@ -197,24 +197,21 @@ static inline struct uffd_msg userfault_msg(unsigned long address,
 	msg_init(&msg);
 	msg.event = UFFD_EVENT_PAGEFAULT;
 	msg.arg.pagefault.address = address;
+	/*
+	 * These flags indicate why the userfault occurred:
+	 * - UFFD_PAGEFAULT_FLAG_WP indicates a write protect fault.
+	 * - UFFD_PAGEFAULT_FLAG_MINOR indicates a minor fault.
+	 * - Neither of these flags being set indicates a MISSING fault.
+	 *
+	 * Separately, UFFD_PAGEFAULT_FLAG_WRITE indicates it was a write
+	 * fault. Otherwise, it was a read fault.
+	 */
 	if (flags & FAULT_FLAG_WRITE)
-		/*
-		 * If UFFD_FEATURE_PAGEFAULT_FLAG_WP was set in the
-		 * uffdio_api.features and UFFD_PAGEFAULT_FLAG_WRITE
-		 * was not set in a UFFD_EVENT_PAGEFAULT, it means it
-		 * was a read fault, otherwise if set it means it's
-		 * a write fault.
-		 */
 		msg.arg.pagefault.flags |= UFFD_PAGEFAULT_FLAG_WRITE;
 	if (reason & VM_UFFD_WP)
-		/*
-		 * If UFFD_FEATURE_PAGEFAULT_FLAG_WP was set in the
-		 * uffdio_api.features and UFFD_PAGEFAULT_FLAG_WP was
-		 * not set in a UFFD_EVENT_PAGEFAULT, it means it was
-		 * a missing fault, otherwise if set it means it's a
-		 * write protect fault.
-		 */
 		msg.arg.pagefault.flags |= UFFD_PAGEFAULT_FLAG_WP;
+	if (reason & VM_UFFD_MINOR)
+		msg.arg.pagefault.flags |= UFFD_PAGEFAULT_FLAG_MINOR;
 	if (features & UFFD_FEATURE_THREAD_ID)
 		msg.arg.pagefault.feat.ptid = task_pid_vnr(current);
 	return msg;
@@ -401,8 +398,10 @@ vm_fault_t handle_userfault(struct vm_fault *vmf, unsigned long reason)
 
 	BUG_ON(ctx->mm != mm);
 
-	VM_BUG_ON(reason & ~(VM_UFFD_MISSING|VM_UFFD_WP));
-	VM_BUG_ON(!(reason & VM_UFFD_MISSING) ^ !!(reason & VM_UFFD_WP));
+	/* Any unrecognized flag is a bug. */
+	VM_BUG_ON(reason & ~__VM_UFFD_FLAGS);
+	/* 0 or > 1 flags set is a bug; we expect exactly 1. */
+	VM_BUG_ON(!reason || (reason & (reason - 1)));
 
 	if (ctx->features & UFFD_FEATURE_SIGBUS)
 		goto out;
@@ -612,7 +611,7 @@ static void userfaultfd_event_wait_completion(struct userfaultfd_ctx *ctx,
 		for (vma = mm->mmap; vma; vma = vma->vm_next)
 			if (vma->vm_userfaultfd_ctx.ctx == release_new_ctx) {
 				vma->vm_userfaultfd_ctx = NULL_VM_UFFD_CTX;
-				vma->vm_flags &= ~(VM_UFFD_WP | VM_UFFD_MISSING);
+				vma->vm_flags &= ~__VM_UFFD_FLAGS;
 			}
 		mmap_write_unlock(mm);
 
@@ -644,7 +643,7 @@ int dup_userfaultfd(struct vm_area_struct *vma, struct list_head *fcs)
 	octx = vma->vm_userfaultfd_ctx.ctx;
 	if (!octx || !(octx->features & UFFD_FEATURE_EVENT_FORK)) {
 		vma->vm_userfaultfd_ctx = NULL_VM_UFFD_CTX;
-		vma->vm_flags &= ~(VM_UFFD_WP | VM_UFFD_MISSING);
+		vma->vm_flags &= ~__VM_UFFD_FLAGS;
 		return 0;
 	}
 
@@ -726,7 +725,7 @@ void mremap_userfaultfd_prep(struct vm_area_struct *vma,
 	} else {
 		/* Drop uffd context if remap feature not enabled */
 		vma->vm_userfaultfd_ctx = NULL_VM_UFFD_CTX;
-		vma->vm_flags &= ~(VM_UFFD_WP | VM_UFFD_MISSING);
+		vma->vm_flags &= ~__VM_UFFD_FLAGS;
 	}
 }
 
@@ -867,12 +866,12 @@ static int userfaultfd_release(struct inode *inode, struct file *file)
 	for (vma = mm->mmap; vma; vma = vma->vm_next) {
 		cond_resched();
 		BUG_ON(!!vma->vm_userfaultfd_ctx.ctx ^
-		       !!(vma->vm_flags & (VM_UFFD_MISSING | VM_UFFD_WP)));
+		       !!(vma->vm_flags & __VM_UFFD_FLAGS));
 		if (vma->vm_userfaultfd_ctx.ctx != ctx) {
 			prev = vma;
 			continue;
 		}
-		new_flags = vma->vm_flags & ~(VM_UFFD_MISSING | VM_UFFD_WP);
+		new_flags = vma->vm_flags & ~__VM_UFFD_FLAGS;
 		prev = vma_merge(mm, prev, vma->vm_start, vma->vm_end,
 				 new_flags, vma->anon_vma,
 				 vma->vm_file, vma->vm_pgoff,
@@ -1262,9 +1261,19 @@ static inline bool vma_can_userfault(struct vm_area_struct *vma,
 				     unsigned long vm_flags)
 {
 	/* FIXME: add WP support to hugetlbfs and shmem */
-	return vma_is_anonymous(vma) ||
-		((is_vm_hugetlb_page(vma) || vma_is_shmem(vma)) &&
-		 !(vm_flags & VM_UFFD_WP));
+	if (vm_flags & VM_UFFD_WP) {
+		if (is_vm_hugetlb_page(vma) || vma_is_shmem(vma))
+			return false;
+	}
+
+	if (vm_flags & VM_UFFD_MINOR) {
+		/* FIXME: Add minor fault interception for shmem. */
+		if (!is_vm_hugetlb_page(vma))
+			return false;
+	}
+
+	return vma_is_anonymous(vma) || is_vm_hugetlb_page(vma) ||
+	       vma_is_shmem(vma);
 }
 
 static int userfaultfd_register(struct userfaultfd_ctx *ctx,
@@ -1290,14 +1299,19 @@ static int userfaultfd_register(struct userfaultfd_ctx *ctx,
 	ret = -EINVAL;
 	if (!uffdio_register.mode)
 		goto out;
-	if (uffdio_register.mode & ~(UFFDIO_REGISTER_MODE_MISSING|
-				     UFFDIO_REGISTER_MODE_WP))
+	if (uffdio_register.mode & ~UFFD_API_REGISTER_MODES)
 		goto out;
 	vm_flags = 0;
 	if (uffdio_register.mode & UFFDIO_REGISTER_MODE_MISSING)
 		vm_flags |= VM_UFFD_MISSING;
 	if (uffdio_register.mode & UFFDIO_REGISTER_MODE_WP)
 		vm_flags |= VM_UFFD_WP;
+	if (uffdio_register.mode & UFFDIO_REGISTER_MODE_MINOR) {
+#ifndef CONFIG_HAVE_ARCH_USERFAULTFD_MINOR
+		goto out;
+#endif
+		vm_flags |= VM_UFFD_MINOR;
+	}
 
 	ret = validate_range(mm, &uffdio_register.range.start,
 			     uffdio_register.range.len);
@@ -1341,7 +1355,7 @@ static int userfaultfd_register(struct userfaultfd_ctx *ctx,
 		cond_resched();
 
 		BUG_ON(!!cur->vm_userfaultfd_ctx.ctx ^
-		       !!(cur->vm_flags & (VM_UFFD_MISSING | VM_UFFD_WP)));
+		       !!(cur->vm_flags & __VM_UFFD_FLAGS));
 
 		/* check not compatible vmas */
 		ret = -EINVAL;
@@ -1421,8 +1435,7 @@ static int userfaultfd_register(struct userfaultfd_ctx *ctx,
 			start = vma->vm_start;
 		vma_end = min(end, vma->vm_end);
 
-		new_flags = (vma->vm_flags &
-			     ~(VM_UFFD_MISSING|VM_UFFD_WP)) | vm_flags;
+		new_flags = (vma->vm_flags & ~__VM_UFFD_FLAGS) | vm_flags;
 		prev = vma_merge(mm, prev, start, vma_end, new_flags,
 				 vma->anon_vma, vma->vm_file, vma->vm_pgoff,
 				 vma_policy(vma),
@@ -1544,7 +1557,7 @@ static int userfaultfd_unregister(struct userfaultfd_ctx *ctx,
 		cond_resched();
 
 		BUG_ON(!!cur->vm_userfaultfd_ctx.ctx ^
-		       !!(cur->vm_flags & (VM_UFFD_MISSING | VM_UFFD_WP)));
+		       !!(cur->vm_flags & __VM_UFFD_FLAGS));
 
 		/*
 		 * Check not compatible vmas, not strictly required
@@ -1595,7 +1608,7 @@ static int userfaultfd_unregister(struct userfaultfd_ctx *ctx,
 			wake_userfault(vma->vm_userfaultfd_ctx.ctx, &range);
 		}
 
-		new_flags = vma->vm_flags & ~(VM_UFFD_MISSING | VM_UFFD_WP);
+		new_flags = vma->vm_flags & ~__VM_UFFD_FLAGS;
 		prev = vma_merge(mm, prev, start, vma_end, new_flags,
 				 vma->anon_vma, vma->vm_file, vma->vm_pgoff,
 				 vma_policy(vma),
@@ -1863,6 +1876,9 @@ 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;
+#endif
 	uffdio_api.ioctls = UFFD_API_IOCTLS;
 	ret = -EFAULT;
 	if (copy_to_user(buf, &uffdio_api, sizeof(uffdio_api)))