io-mapping: ensure io_mapping_map_atomic _is_ atomic

For the !HAVE_ATOMIC_IOMAP case the stub functions did not call
pagefault_disable/_enable. The i915 driver relies on the map
actually being atomic, otherwise it can deadlock with it's own
pagefault handler in the gtt pwrite fastpath.

This is exercised by gem_mmap_gtt from the intel-gpu-toosl gem
testsuite.

v2: Chris Wilson noted the lack of an include.

Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=38115
Cc: stable@kernel.org
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Reviewed-by: Chris Wilson <chris@chris-wilson.co.uk>
Signed-off-by: Keith Packard <keithp@keithp.com>

include/linux/io-mapping.h

@@ -117,6 +117,8 @@ io_mapping_unmap(void __iomem *vaddr)
 
 #else
 
+#include <linux/uaccess.h>
+
 /* this struct isn't actually defined anywhere */
 struct io_mapping;
 
@@ -138,12 +140,14 @@ static inline void __iomem *
 io_mapping_map_atomic_wc(struct io_mapping *mapping,
 			 unsigned long offset)
 {
+	pagefault_disable();
 	return ((char __force __iomem *) mapping) + offset;
 }
 
 static inline void
 io_mapping_unmap_atomic(void __iomem *vaddr)
 {
+	pagefault_enable();
 }
 
 /* Non-atomic map/unmap */