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-rw-r--r--kernel/drivers/xen/preempt.c44
1 files changed, 44 insertions, 0 deletions
diff --git a/kernel/drivers/xen/preempt.c b/kernel/drivers/xen/preempt.c
new file mode 100644
index 000000000..a1800c150
--- /dev/null
+++ b/kernel/drivers/xen/preempt.c
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+/*
+ * Preemptible hypercalls
+ *
+ * Copyright (C) 2014 Citrix Systems R&D ltd.
+ *
+ * This source code is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU General Public License as
+ * published by the Free Software Foundation; either version 2 of the
+ * License, or (at your option) any later version.
+ */
+
+#include <linux/sched.h>
+#include <xen/xen-ops.h>
+
+#ifndef CONFIG_PREEMPT
+
+/*
+ * Some hypercalls issued by the toolstack can take many 10s of
+ * seconds. Allow tasks running hypercalls via the privcmd driver to
+ * be voluntarily preempted even if full kernel preemption is
+ * disabled.
+ *
+ * Such preemptible hypercalls are bracketed by
+ * xen_preemptible_hcall_begin() and xen_preemptible_hcall_end()
+ * calls.
+ */
+
+DEFINE_PER_CPU(bool, xen_in_preemptible_hcall);
+EXPORT_SYMBOL_GPL(xen_in_preemptible_hcall);
+
+asmlinkage __visible void xen_maybe_preempt_hcall(void)
+{
+ if (unlikely(__this_cpu_read(xen_in_preemptible_hcall)
+ && should_resched())) {
+ /*
+ * Clear flag as we may be rescheduled on a different
+ * cpu.
+ */
+ __this_cpu_write(xen_in_preemptible_hcall, false);
+ _cond_resched();
+ __this_cpu_write(xen_in_preemptible_hcall, true);
+ }
+}
+#endif /* CONFIG_PREEMPT */