kmsan: core: kmsan_in_runtime() should return true in NMI context

Without that, every call to __msan_poison_alloca() in NMI may end up
allocating memory, which is NMI-unsafe.

Link: https://lkml.kernel.org/r/[e-mail]
Link: https://lore.kernel.org/lkml/[e-mail]/
Signed-off-by: Alexander Potapenko <[e-mail]>
Acked-by: Peter Zijlstra (Intel) <[e-mail]>
Cc: Dmitry Vyukov <[e-mail]>
Cc: Marco Elver <[e-mail]>
Cc: Borislav Petkov <[e-mail]>
Cc: Dave Hansen <[e-mail]>
Cc: Ingo Molnar <[e-mail]>
Cc: Kees Cook <[e-mail]>
Cc: Masahiro Yamada <[e-mail]>
Cc: Nick Desaulniers <[e-mail]>
Cc: Thomas Gleixner <[e-mail]>
Signed-off-by: Andrew Morton <[e-mail]>

mm/kmsan/kmsan.h

···
 {
 	if ((hardirq_count() >> HARDIRQ_SHIFT) > 1)
 		return true;
+	if (in_nmi())
+		return true;
 	return kmsan_get_context()->kmsan_in_runtime;
 }