x86-64, init: Do not set NX bits on non-NX capable hardware

x86-64, init: Do not set NX bits on non-NX capable hardware

commit 78d77df71510a96e042de7ba6dbd7998103642cb upstream.

During early init, we would incorrectly set the NX bit even if the NX
feature was not supported.  Instead, only set this bit if NX is
actually available and enabled.  We already do very early detection of
the NX bit to enable it in EFER, this simply extends this detection to
the early page table mask.

Reported-by: Fernando Luis Vázquez Cao <fernando@oss.ntt.co.jp>
Signed-off-by: H. Peter Anvin <hpa@linux.intel.com>
Link: http://lkml.kernel.org/r/1367476850.5660.2.camel@nexus
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>