x86/cpuid: Tie SMAP to NX, for the shadow pagetable code

NX support in the host is required for the shadow pagetable code to handle
SMAP correctly for guests.

Signed-off-by: Andrew Cooper <andrew.cooper3@citrix.com>
Acked-by: Jan Beulich <jbeulich@suse.com>

xen/tools/gen-cpuid.py

@@ -239,6 +239,11 @@ def crunch_numbers(state):
         # absence of any enabled xstate.
         AVX: [FMA, FMA4, F16C, AVX2, XOP],
 
+        # This dependency exists solely for the shadow pagetable code.  If the
+        # host doesn't have NX support, the shadow pagetable code can't handle
+        # SMAP correctly for guests.
+        NX: [SMAP],
+
         # CX16 is only encodable in Long Mode.  LAHF_LM indicates that the
         # SAHF/LAHF instructions are reintroduced in Long Mode.  1GB
         # superpages, PCID and PKU are only available in 4 level paging.