LXR linux/drivers/xen/preempt.c

   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_PREEMPTION
  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                local_irq_enable();
  37                cond_resched();
  38                local_irq_disable();
  39                __this_cpu_write(xen_in_preemptible_hcall, true);
  40        }
  41}
  42#endif /* CONFIG_PREEMPTION */
  43