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fdfd811d DV |
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 | ||
28 | DEFINE_PER_CPU(bool, xen_in_preemptible_hcall); | |
29 | EXPORT_SYMBOL_GPL(xen_in_preemptible_hcall); | |
30 | ||
31 | asmlinkage __visible void xen_maybe_preempt_hcall(void) | |
32 | { | |
33 | if (unlikely(__this_cpu_read(xen_in_preemptible_hcall) | |
0fa2f5cb | 34 | && need_resched())) { |
fdfd811d DV |
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 */ |