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_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
  24 DEFINE_PER_CPU(bool, xen_in_preemptible_hcall);
  25 EXPORT_SYMBOL_GPL(xen_in_preemptible_hcall);
  26
  27 asmlinkage __visible void xen_maybe_preempt_hcall(void)
  28 {
  29         if (unlikely(__this_cpu_read(xen_in_preemptible_hcall)
  30                      && need_resched() && !preempt_count())) {
  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_PREEMPT */