On Fri, Sep 04, 2020 at 04:31:43PM -0400, Gabriel Krisman Bertazi wrote:

+struct syscall_user_dispatch {
+	char __user *selector;
+	unsigned long dispatcher_start;
+	unsigned long dispatcher_end;
+};

+int do_syscall_user_dispatch(struct pt_regs *regs)
+{
+	struct syscall_user_dispatch *sd = &current->syscall_dispatch;
+	unsigned long ip = instruction_pointer(regs);
+	char state;
+
+	if (likely(ip >= sd->dispatcher_start && ip <= sd->dispatcher_end))
+		return 0;

If you use {offset,size}, instead of {start,end}, you can write the
above like:

	if (ip - sd->dispatcher_offset < sd->dispatcher_size)
		return 0;

which is just a single branch.