pagemap: hide physical addresses from non-privileged users

pagemap: hide physical addresses from non-privileged users

This patch makes pagemap readable for normal users and hides physical
addresses from them.  For some use-cases PFN isn't required at all.

See http://lkml.kernel.org/r/1425935472[email protected]

Fixes: ab676b7d6fbf ("pagemap: do not leak physical addresses to non-privileged userspace")
Signed-off-by: Konstantin Khlebnikov <[email protected]>
Cc: Naoya Horiguchi <[email protected]>
Reviewed-by: Mark Williamson <[email protected]>
Tested-by:  Mark Williamson <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>
Signed-off-by: Linus Torvalds <[email protected]>