x86/xen: Fix noinstr fail in xen_pv_evtchn_do_upcall()

Fix:

  vmlinux.o: warning: objtool: xen_pv_evtchn_do_upcall()+0x23: call to irq_enter_rcu() leaves .noinstr.text section

Fixes: 359f01d1 ("x86/entry: Use run_sysvec_on_irqstack_cond() for XEN upcall")
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Link: https://lore.kernel.org/r/20210621120120.532960208@infradead.org

arch/x86/entry/common.c

@@ -269,15 +269,16 @@ __visible noinstr void xen_pv_evtchn_do_upcall(struct pt_regs *regs)
 	irqentry_state_t state = irqentry_enter(regs);
 	bool inhcall;
 
+	instrumentation_begin();
 	run_sysvec_on_irqstack_cond(__xen_pv_evtchn_do_upcall, regs);
 
 	inhcall = get_and_clear_inhcall();
 	if (inhcall && !WARN_ON_ONCE(state.exit_rcu)) {
-		instrumentation_begin();
 		irqentry_exit_cond_resched();
 		instrumentation_end();
 		restore_inhcall(inhcall);
 	} else {
+		instrumentation_end();
 		irqentry_exit(regs, state);
 	}
 }