x86-32: make sure virt_addr_valid() returns false for fixmap addresses

I found that virt_addr_valid() was returning true for fixmap addresses.

I'm not sure whether pfn_valid() is supposed to include this test,
but there's no harm in being explicit.
Signed-off-by: NJeremy Fitzhardinge <jeremy.fitzhardinge@citrix.com>
Cc: Jiri Slaby <jirislaby@gmail.com>
Cc: Yinghai Lu <yinghai@kernel.org>
LKML-Reference: <49B166D6.2080505@goop.org>
Signed-off-by: NIngo Molnar <mingo@elte.hu>

arch/x86/mm/ioremap.c

@@ -87,6 +87,8 @@ bool __virt_addr_valid(unsigned long x)
 		return false;
 	if (__vmalloc_start_set && is_vmalloc_addr((void *) x))
 		return false;
+	if (x >= FIXADDR_START)
+		return false;
 	return pfn_valid((x - PAGE_OFFSET) >> PAGE_SHIFT);
 }
 EXPORT_SYMBOL(__virt_addr_valid);