x86/mm: Prevent bogus warnings with "noexec=off"

Xose Vazquez Perez reported boot warnings when NX is disabled on the kernel command line.

__early_set_fixmap() triggers this warning:

  attempted to set unsupported pgprot:    8000000000000163
			       bits:      8000000000000000
			       supported: 7fffffffffffffff

  WARNING: CPU: 0 PID: 0 at arch/x86/include/asm/pgtable.h:537
			    __early_set_fixmap+0xa2/0xff

because it uses __default_kernel_pte_mask to mask out unsupported bits.

Use __supported_pte_mask instead.

Disabling NX on the command line also triggers the NX warning in the page
table mapping check:

  WARNING: CPU: 1 PID: 1 at arch/x86/mm/dump_pagetables.c:262 note_page+0x2ae/0x650
  ....

Make the warning depend on NX set in __supported_pte_mask.

Reported-by: Xose Vazquez Perez <xose.vazquez@gmail.com>
Tested-by: Xose Vazquez Perez <xose.vazquez@gmail.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Cc: Andy Lutomirski <luto@kernel.org>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Dave Hansen <dave.hansen@linux.intel.com>
Cc: H. Peter Anvin <hpa@zytor.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Rik van Riel <riel@surriel.com>
Link: http://lkml.kernel.org/r/alpine.DEB.2.21.1904151037530.1729@nanos.tec.linutronix.de
Signed-off-by: Ingo Molnar <mingo@kernel.org>

arch/x86/mm/dump_pagetables.c

@@ -259,7 +259,8 @@ static void note_wx(struct pg_state *st)
 #endif
 	/* Account the WX pages */
 	st->wx_pages += npages;
-	WARN_ONCE(1, "x86/mm: Found insecure W+X mapping at address %pS\n",
+	WARN_ONCE(__supported_pte_mask & _PAGE_NX,
+		  "x86/mm: Found insecure W+X mapping at address %pS\n",
 		  (void *)st->start_address);
 }
 

arch/x86/mm/ioremap.c

@@ -825,7 +825,7 @@ void __init __early_set_fixmap(enum fixed_addresses idx,
 	pte = early_ioremap_pte(addr);
 
 	/* Sanitize 'prot' against any unsupported bits: */
-	pgprot_val(flags) &= __default_kernel_pte_mask;
+	pgprot_val(flags) &= __supported_pte_mask;
 
 	if (pgprot_val(flags))
 		set_pte(pte, pfn_pte(phys >> PAGE_SHIFT, flags));