powerpc: Allow 64bit VDSO __kernel_sync_dicache to work across ranges >4GB

powerpc: Allow 64bit VDSO __kernel_sync_dicache to work across ranges >4GB

commit f9ec11165301982585e5e5f606739b5bae5331f3 upstream.

When calling __kernel_sync_dicache with a size >4GB, we were masking
off the upper 32 bits, so we would incorrectly flush a range smaller
than intended.

This patch replaces the 32 bit shifts with 64 bit ones, so that
the full size is accounted for.

Signed-off-by: Alastair D'Silva <alastair@d-silva.org>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/20191104023305.9581-3-alastair@au1.ibm.com
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>