powerpc/mm: tracking vDSO remap

powerpc/mm: tracking vDSO remap

Some processes (CRIU) are moving the vDSO area using the mremap system
call.  As a consequence the kernel reference to the vDSO base address is
no more valid and the signal return frame built once the vDSO has been
moved is not pointing to the new sigreturn address.

This patch handles vDSO remapping and unmapping.

Signed-off-by: Laurent Dufour <[email protected]>
Reviewed-by: Ingo Molnar <[email protected]>
Cc: "Kirill A. Shutemov" <[email protected]>
Cc: Hugh Dickins <[email protected]>
Cc: Rik van Riel <[email protected]>
Cc: Mel Gorman <[email protected]>
Cc: Pavel Emelyanov <[email protected]>
Cc: Benjamin Herrenschmidt <[email protected]>
Cc: Paul Mackerras <[email protected]>
Cc: Michael Ellerman <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>
Signed-off-by: Linus Torvalds <[email protected]>