Revert "x86/mm/32: Set NX in __supported_pte_mask before enabling paging"

This reverts commit 320d25b6a05f8b73c23fc21025d2906ecdd2d4fc.

This change was problematic for a couple of reasons:

1. It missed a some entry points (Xen things and 64-bit native).

2. The entry it changed can be executed more than once. This isn't
really a problem, but it conflated per-cpu state setup and global
state setup.

3. It broke 64-bit non-NX. 64-bit non-NX worked the other way around from
32-bit -- __supported_pte_mask had NX set initially and was *cleared*
in x86_configure_nx. With the patch applied, it never got cleared.

Reported-and-tested-by: Meelis Roos <[e-mail]>
Signed-off-by: Andy Lutomirski <[e-mail]>
Cc: Andy Lutomirski <[e-mail]>
Cc: Borislav Petkov <[e-mail]>
Cc: Brian Gerst <[e-mail]>
Cc: Denys Vlasenko <[e-mail]>
Cc: H. Peter Anvin <[e-mail]>
Cc: Linus Torvalds <[e-mail]>
Cc: Mike Galbraith <[e-mail]>
Cc: Peter Zijlstra <[e-mail]>
Cc: Thomas Gleixner <[e-mail]>
Link: http://lkml.kernel.org/r/[e-mail]
Signed-off-by: Ingo Molnar <[e-mail]>

arch/x86/kernel/head_32.S

···
 	/* Make changes effective */
 	wrmsr
 
-	/*
-	 * And make sure that all the mappings we set up have NX set from
-	 * the beginning.
-	 */
-	orl $(1 << (_PAGE_BIT_NX - 32)), pa(__supported_pte_mask + 4)
-
 enable_paging:
 
 /*

arch/x86/mm/setup_nx.c

···
 
 void x86_configure_nx(void)
 {
-	/* If disable_nx is set, clear NX on all new mappings going forward. */
-	if (disable_nx)
+	if (boot_cpu_has(X86_FEATURE_NX) && !disable_nx)
+		__supported_pte_mask |= _PAGE_NX;
+	else
 		__supported_pte_mask &= ~_PAGE_NX;
 }