Allow guest to specify syscall vector to use.

(Based on Ron Minnich's LGUEST_PLAN9_SYSCALL patch).

This patch allows Guests to specify what system call vector they want,
and we try to reserve it.  We only allow one non-Linux system call
vector, to try to avoid DoS on the Host.

Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>

drivers/lguest/x86/core.c

@@ -530,6 +530,10 @@ int lguest_arch_init_hypercalls(struct lguest *lg)
 	if (put_user(tsc_speed, &lg->lguest_data->tsc_khz))
 		return -EFAULT;
 
+	/* The interrupt code might not like the system call vector. */
+	if (!check_syscall_vector(lg))
+		kill_guest(lg, "bad syscall vector");
+
 	return 0;
 }
 /* Now we've examined the hypercall code; our Guest can make requests.  There