1// SPDX-License-Identifier: GPL-2.0-or-later
 2/*
 3 * Preemptible hypercalls
 4 *
 5 * Copyright (C) 2014 Citrix Systems R&D ltd.
 6 */
 7
 8#include <linux/sched.h>
 9#include <xen/xen-ops.h>
10
11#ifndef CONFIG_PREEMPT
12
13/*
14 * Some hypercalls issued by the toolstack can take many 10s of
15 * seconds. Allow tasks running hypercalls via the privcmd driver to
16 * be voluntarily preempted even if full kernel preemption is
17 * disabled.
18 *
19 * Such preemptible hypercalls are bracketed by
20 * xen_preemptible_hcall_begin() and xen_preemptible_hcall_end()
21 * calls.
22 */
23
24DEFINE_PER_CPU(bool, xen_in_preemptible_hcall);
25EXPORT_SYMBOL_GPL(xen_in_preemptible_hcall);
26
27asmlinkage __visible void xen_maybe_preempt_hcall(void)
28{
29	if (unlikely(__this_cpu_read(xen_in_preemptible_hcall)
30		     && need_resched())) {
31		/*
32		 * Clear flag as we may be rescheduled on a different
33		 * cpu.
34		 */
35		__this_cpu_write(xen_in_preemptible_hcall, false);
36		_cond_resched();
37		__this_cpu_write(xen_in_preemptible_hcall, true);
38	}
39}
40#endif /* CONFIG_PREEMPT */