1/*
2 * Preemptible hypercalls
3 *
4 * Copyright (C) 2014 Citrix Systems R&D ltd.
5 *
6 * This source code is free software; you can redistribute it and/or
7 * modify it under the terms of the GNU General Public License as
8 * published by the Free Software Foundation; either version 2 of the
9 * License, or (at your option) any later version.
10 */
11
12#include <linux/sched.h>
13#include <xen/xen-ops.h>
14
15#ifndef CONFIG_PREEMPT
16
17/*
18 * Some hypercalls issued by the toolstack can take many 10s of
19 * seconds. Allow tasks running hypercalls via the privcmd driver to
20 * be voluntarily preempted even if full kernel preemption is
21 * disabled.
22 *
23 * Such preemptible hypercalls are bracketed by
24 * xen_preemptible_hcall_begin() and xen_preemptible_hcall_end()
25 * calls.
26 */
27
28DEFINE_PER_CPU(bool, xen_in_preemptible_hcall);
29EXPORT_SYMBOL_GPL(xen_in_preemptible_hcall);
30
31asmlinkage __visible void xen_maybe_preempt_hcall(void)
32{
33 if (unlikely(__this_cpu_read(xen_in_preemptible_hcall)
34 && need_resched())) {
35 /*
36 * Clear flag as we may be rescheduled on a different
37 * cpu.
38 */
39 __this_cpu_write(xen_in_preemptible_hcall, false);
40 _cond_resched();
41 __this_cpu_write(xen_in_preemptible_hcall, true);
42 }
43}
44#endif /* CONFIG_PREEMPT */
45