1 files changed, 65 insertions, 1 deletions
diff --git a/mm/gup.c b/mm/gup.c
index dfcde13f289a..d3fb60e5bfac 100644
--- a/mm/gup.c
+++ b/mm/gup.c
@@ -66,7 +66,7 @@ static int follow_pfn_pte(struct vm_area_struct *vma, unsigned long address,
  */
 static inline bool can_follow_write_pte(pte_t pte, unsigned int flags)
 {
-	return pte_write(pte) ||
+	return pte_access_permitted(pte, WRITE) ||
 		((flags & FOLL_FORCE) && (flags & FOLL_COW) && pte_dirty(pte));
 }
 
@@ -1095,6 +1095,70 @@ long get_user_pages(unsigned long start, unsigned long nr_pages,
 }
 EXPORT_SYMBOL(get_user_pages);
 
+#ifdef CONFIG_FS_DAX
+/*
+ * This is the same as get_user_pages() in that it assumes we are
+ * operating on the current task's mm, but it goes further to validate
+ * that the vmas associated with the address range are suitable for
+ * longterm elevated page reference counts. For example, filesystem-dax
+ * mappings are subject to the lifetime enforced by the filesystem and
+ * we need guarantees that longterm users like RDMA and V4L2 only
+ * establish mappings that have a kernel enforced revocation mechanism.
+ *
+ * "longterm" == userspace controlled elevated page count lifetime.
+ * Contrast this to iov_iter_get_pages() usages which are transient.
+ */
+long get_user_pages_longterm(unsigned long start, unsigned long nr_pages,
+		unsigned int gup_flags, struct page **pages,
+		struct vm_area_struct **vmas_arg)
+{
+	struct vm_area_struct **vmas = vmas_arg;
+	struct vm_area_struct *vma_prev = NULL;
+	long rc, i;
+
+	if (!pages)
+		return -EINVAL;
+
+	if (!vmas) {
+		vmas = kcalloc(nr_pages, sizeof(struct vm_area_struct *),
+			       GFP_KERNEL);
+		if (!vmas)
+			return -ENOMEM;
+	}
+
+	rc = get_user_pages(start, nr_pages, gup_flags, pages, vmas);
+
+	for (i = 0; i < rc; i++) {
+		struct vm_area_struct *vma = vmas[i];
+
+		if (vma == vma_prev)
+			continue;
+
+		vma_prev = vma;
+
+		if (vma_is_fsdax(vma))
+			break;
+	}
+
+	/*
+	 * Either get_user_pages() failed, or the vma validation
+	 * succeeded, in either case we don't need to put_page() before
+	 * returning.
+	 */
+	if (i >= rc)
+		goto out;
+
+	for (i = 0; i < rc; i++)
+		put_page(pages[i]);
+	rc = -EOPNOTSUPP;
+out:
+	if (vmas != vmas_arg)
+		kfree(vmas);
+	return rc;
+}
+EXPORT_SYMBOL(get_user_pages_longterm);
+#endif /* CONFIG_FS_DAX */
+
 /**
  * populate_vma_page_range() -  populate a range of pages in the vma.
  * @vma:   target vma