xen: set _PAGE_NX in __supported_pte_mask before pagetable construction

Some 64-bit machines don't support the NX flag in ptes.
Check for NX before constructing the kernel pagetables.

Signed-off-by: Jeremy Fitzhardinge <[e-mail]>

arch/x86/xen/enlighten.c

···
 #include <asm/xen/hypervisor.h>
 #include <asm/fixmap.h>
 #include <asm/processor.h>
+#include <asm/proto.h>
 #include <asm/msr-index.h>
 #include <asm/setup.h>
 #include <asm/desc.h>
···
 	.emergency_restart = xen_emergency_restart,
 };
 
-
 /* First C function to be called on Xen boot */
 asmlinkage void __init xen_start_kernel(void)
 {
···
 	__supported_pte_mask &= ~_PAGE_GLOBAL;
 	if (!xen_initial_domain())
 		__supported_pte_mask &= ~(_PAGE_PWT | _PAGE_PCD);
+
+#ifdef CONFIG_X86_64
+	/* Work out if we support NX */
+	check_efer();
+#endif
 
 	/* Don't do the full vcpu_info placement stuff until we have a
 	   possible map and a non-dummy shared_info. */