1 files changed, 29 insertions, 0 deletions
diff --git a/mm/gup.c b/mm/gup.c
index f598a037eb04..501bc150792c 100644
--- a/mm/gup.c
+++ b/mm/gup.c
@@ -1648,6 +1648,35 @@ out:
 }
 EXPORT_SYMBOL(fault_in_writeable);
 
+/**
+ * fault_in_subpage_writeable - fault in an address range for writing
+ * @uaddr: start of address range
+ * @size: size of address range
+ *
+ * Fault in a user address range for writing while checking for permissions at
+ * sub-page granularity (e.g. arm64 MTE). This function should be used when
+ * the caller cannot guarantee forward progress of a copy_to_user() loop.
+ *
+ * Returns the number of bytes not faulted in (like copy_to_user() and
+ * copy_from_user()).
+ */
+size_t fault_in_subpage_writeable(char __user *uaddr, size_t size)
+{
+	size_t faulted_in;
+
+	/*
+	 * Attempt faulting in at page granularity first for page table
+	 * permission checking. The arch-specific probe_subpage_writeable()
+	 * functions may not check for this.
+	 */
+	faulted_in = size - fault_in_writeable(uaddr, size);
+	if (faulted_in)
+		faulted_in -= probe_subpage_writeable(uaddr, faulted_in);
+
+	return size - faulted_in;
+}
+EXPORT_SYMBOL(fault_in_subpage_writeable);
+
 /*
  * fault_in_safe_writeable - fault in an address range for writing
  * @uaddr: start of address range