If we can prevent stray writes from landing in the scratch page, we can
reuse the same page and same scratch PT for all contexts without fear of
information leaks and side-channels.
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Matthew Auld <matthew.auld@intel.com>
Reviewed-by: Matthew Auld <matthew.auld@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20181029182721.29568-2-chris@chris-wilson.co.uk