arm64: compat: Add separate CP15 trapping hook

Instead of directly generating an UNDEF when trapping a CP15 access,
let's add a new entry point to that effect (which only generates an
UNDEF for now).

Acked-by: Mark Rutland <mark.rutland@arm.com>
Signed-off-by: Marc Zyngier <marc.zyngier@arm.com>
Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>

arch/arm64/kernel/traps.c

@@ -547,6 +547,19 @@ static struct sys64_hook sys64_hooks[] = {
 	{},
 };
 
+
+#ifdef CONFIG_COMPAT
+asmlinkage void __exception do_cp15instr(unsigned int esr, struct pt_regs *regs)
+{
+	/*
+	 * New cp15 instructions may previously have been undefined at
+	 * EL0. Fall back to our usual undefined instruction handler
+	 * so that we handle these consistently.
+	 */
+	do_undefinstr(regs);
+}
+#endif
+
 asmlinkage void __exception do_sysinstr(unsigned int esr, struct pt_regs *regs)
 {
 	struct sys64_hook *hook;